text: // Copyright 2012 the V8 project authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  /** \mainpage V8 API Reference Guide
   *
   * V8 is Google's open source JavaScript engine.
   *
   * This set of documents provides reference material generated from the
   * V8 header file, include/v8.h.
   *
   * For other documentation see http://code.google.com/apis/v8/
   */
  
  #ifndef INCLUDE_V8_H_
  #define INCLUDE_V8_H_
  
  #include <stddef.h>
  #include <stdint.h>
  #include <stdio.h>
  #include <memory>
  #include <utility>
  #include <vector>
  
  #include "v8-internal.h"  // NOLINT(build/include)
  #include "v8-version.h"   // NOLINT(build/include)
  #include "v8config.h"     // NOLINT(build/include)
  
  // We reserve the V8_* prefix for macros defined in V8 public API and
  // assume there are no name conflicts with the embedder's code.
  
  /**
   * The v8 JavaScript engine.
   */
  namespace v8 {
  
  class AccessorSignature;
  class Array;
  class ArrayBuffer;
  class BigInt;
  class BigIntObject;
  class Boolean;
  class BooleanObject;
  class Context;
  class Data;
  class Date;
  class External;
  class Function;
  class FunctionTemplate;
  class HeapProfiler;
  class ImplementationUtilities;
  class Int32;
  class Integer;
  class Isolate;
  template <class T>
  class Maybe;
  class MicrotaskQueue;
  class Name;
  class Number;
  class NumberObject;
  class Object;
  class ObjectOperationDescriptor;
  class ObjectTemplate;
  class Platform;
  class Primitive;
  class Promise;
  class PropertyDescriptor;
  class Proxy;
  class RawOperationDescriptor;
  class Script;
  class SharedArrayBuffer;
  class Signature;
  class StartupData;
  class StackFrame;
  class StackTrace;
  class String;
  class StringObject;
  class Symbol;
  class SymbolObject;
  class PrimitiveArray;
  class Private;
  class Uint32;
  class Utils;
  class Value;
  class WasmModuleObject;
  template <class T> class Local;
  template <class T>
  class MaybeLocal;
  template <class T> class Eternal;
  template<class T> class NonCopyablePersistentTraits;
  template<class T> class PersistentBase;
  template <class T, class M = NonCopyablePersistentTraits<T> >
  class Persistent;
  template <class T>
  class Global;
  template <class T>
  class TracedGlobal;
  template<class K, class V, class T> class PersistentValueMap;
  template <class K, class V, class T>
  class PersistentValueMapBase;
  template <class K, class V, class T>
  class GlobalValueMap;
  template<class V, class T> class PersistentValueVector;
  template<class T, class P> class WeakCallbackObject;
  class FunctionTemplate;
  class ObjectTemplate;
  template<typename T> class FunctionCallbackInfo;
  template<typename T> class PropertyCallbackInfo;
  class StackTrace;
  class StackFrame;
  class Isolate;
  class CallHandlerHelper;
  class EscapableHandleScope;
  template<typename T> class ReturnValue;
  
  namespace internal {
  class Arguments;
  class DeferredHandles;
  class Heap;
  class HeapObject;
  class ExternalString;
  class Isolate;
  class LocalEmbedderHeapTracer;
  class MicrotaskQueue;
  struct ScriptStreamingData;
  template<typename T> class CustomArguments;
  class PropertyCallbackArguments;
  class FunctionCallbackArguments;
  class GlobalHandles;
  class ScopedExternalStringLock;
  
  namespace wasm {
  class NativeModule;
  class StreamingDecoder;
  }  // namespace wasm
  
  }  // namespace internal
  
  namespace debug {
  class ConsoleCallArguments;
  }  // namespace debug
  
  // --- Handles ---
  
  #define TYPE_CHECK(T, S)                                       \
    while (false) {                                              \
      *(static_cast<T* volatile*>(0)) = static_cast<S*>(0);      \
    }
  
  /**
   * An object reference managed by the v8 garbage collector.
   *
   * All objects returned from v8 have to be tracked by the garbage
   * collector so that it knows that the objects are still alive.  Also,
   * because the garbage collector may move objects, it is unsafe to
   * point directly to an object.  Instead, all objects are stored in
   * handles which are known by the garbage collector and updated
   * whenever an object moves.  Handles should always be passed by value
   * (except in cases like out-parameters) and they should never be
   * allocated on the heap.
   *
   * There are two types of handles: local and persistent handles.
   *
   * Local handles are light-weight and transient and typically used in
   * local operations.  They are managed by HandleScopes. That means that a
   * HandleScope must exist on the stack when they are created and that they are
   * only valid inside of the HandleScope active during their creation.
   * For passing a local handle to an outer HandleScope, an EscapableHandleScope
   * and its Escape() method must be used.
   *
   * Persistent handles can be used when storing objects across several
   * independent operations and have to be explicitly deallocated when they're no
   * longer used.
   *
   * It is safe to extract the object stored in the handle by
   * dereferencing the handle (for instance, to extract the Object* from
   * a Local<Object>); the value will still be governed by a handle
   * behind the scenes and the same rules apply to these values as to
   * their handles.
   */
  template <class T>
  class Local {
   public:
    V8_INLINE Local() : val_(nullptr) {}
    template <class S>
    V8_INLINE Local(Local<S> that)
        : val_(reinterpret_cast<T*>(*that)) {
      /**
       * This check fails when trying to convert between incompatible
       * handles. For example, converting from a Local<String> to a
       * Local<Number>.
       */
      TYPE_CHECK(T, S);
    }
  
    /**
     * Returns true if the handle is empty.
     */
    V8_INLINE bool IsEmpty() const { return val_ == nullptr; }
  
    /**
     * Sets the handle to be empty. IsEmpty() will then return true.
     */
    V8_INLINE void Clear() { val_ = nullptr; }
  
    V8_INLINE T* operator->() const { return val_; }
  
    V8_INLINE T* operator*() const { return val_; }
  
    /**
     * Checks whether two handles are the same.
     * Returns true if both are empty, or if the objects
     * to which they refer are identical.
     * The handles' references are not checked.
     */
    template <class S>
    V8_INLINE bool operator==(const Local<S>& that) const {
      internal::Address* a = reinterpret_cast<internal::Address*>(this->val_);
      internal::Address* b = reinterpret_cast<internal::Address*>(that.val_);
      if (a == nullptr) return b == nullptr;
      if (b == nullptr) return false;
      return *a == *b;
    }
  
    template <class S> V8_INLINE bool operator==(
        const PersistentBase<S>& that) const {
      internal::Address* a = reinterpret_cast<internal::Address*>(this->val_);
      internal::Address* b = reinterpret_cast<internal::Address*>(that.val_);
      if (a == nullptr) return b == nullptr;
      if (b == nullptr) return false;
      return *a == *b;
    }
  
    /**
     * Checks whether two handles are different.
     * Returns true if only one of the handles is empty, or if
     * the objects to which they refer are different.
     * The handles' references are not checked.
     */
    template <class S>
    V8_INLINE bool operator!=(const Local<S>& that) const {
      return !operator==(that);
    }
  
    template <class S> V8_INLINE bool operator!=(
        const Persistent<S>& that) const {
      return !operator==(that);
    }
  
    /**
     * Cast a handle to a subclass, e.g. Local<Value> to Local<Object>.
     * This is only valid if the handle actually refers to a value of the
     * target type.
     */
    template <class S> V8_INLINE static Local<T> Cast(Local<S> that) {
  #ifdef V8_ENABLE_CHECKS
      // If we're going to perform the type check then we have to check
      // that the handle isn't empty before doing the checked cast.
      if (that.IsEmpty()) return Local<T>();
  #endif
      return Local<T>(T::Cast(*that));
    }
  
    /**
     * Calling this is equivalent to Local<S>::Cast().
     * In particular, this is only valid if the handle actually refers to a value
     * of the target type.
     */
    template <class S>
    V8_INLINE Local<S> As() const {
      return Local<S>::Cast(*this);
    }
  
    /**
     * Create a local handle for the content of another handle.
     * The referee is kept alive by the local handle even when
     * the original handle is destroyed/disposed.
     */
    V8_INLINE static Local<T> New(Isolate* isolate, Local<T> that);
    V8_INLINE static Local<T> New(Isolate* isolate,
                                  const PersistentBase<T>& that);
    V8_INLINE static Local<T> New(Isolate* isolate, const TracedGlobal<T>& that);
  
   private:
    friend class Utils;
    template<class F> friend class Eternal;
    template<class F> friend class PersistentBase;
    template<class F, class M> friend class Persistent;
    template<class F> friend class Local;
    template <class F>
    friend class MaybeLocal;
    template<class F> friend class FunctionCallbackInfo;
    template<class F> friend class PropertyCallbackInfo;
    friend class String;
    friend class Object;
    friend class Context;
    friend class Isolate;
    friend class Private;
    template<class F> friend class internal::CustomArguments;
    friend Local<Primitive> Undefined(Isolate* isolate);
    friend Local<Primitive> Null(Isolate* isolate);
    friend Local<Boolean> True(Isolate* isolate);
    friend Local<Boolean> False(Isolate* isolate);
    friend class HandleScope;
    friend class EscapableHandleScope;
    template <class F1, class F2, class F3>
    friend class PersistentValueMapBase;
    template<class F1, class F2> friend class PersistentValueVector;
    template <class F>
    friend class ReturnValue;
    template <class F>
    friend class TracedGlobal;
  
    explicit V8_INLINE Local(T* that) : val_(that) {}
    V8_INLINE static Local<T> New(Isolate* isolate, T* that);
    T* val_;
  };
  
  
  #if !defined(V8_IMMINENT_DEPRECATION_WARNINGS)
  // Handle is an alias for Local for historical reasons.
  template <class T>
  using Handle = Local<T>;
  #endif
  
  
  /**
   * A MaybeLocal<> is a wrapper around Local<> that enforces a check whether
   * the Local<> is empty before it can be used.
   *
   * If an API method returns a MaybeLocal<>, the API method can potentially fail
   * either because an exception is thrown, or because an exception is pending,
   * e.g. because a previous API call threw an exception that hasn't been caught
   * yet, or because a TerminateExecution exception was thrown. In that case, an
   * empty MaybeLocal is returned.
   */
  template <class T>
  class MaybeLocal {
   public:
    V8_INLINE MaybeLocal() : val_(nullptr) {}
    template <class S>
    V8_INLINE MaybeLocal(Local<S> that)
        : val_(reinterpret_cast<T*>(*that)) {
      TYPE_CHECK(T, S);
    }
  
    V8_INLINE bool IsEmpty() const { return val_ == nullptr; }
  
    /**
     * Converts this MaybeLocal<> to a Local<>. If this MaybeLocal<> is empty,
     * |false| is returned and |out| is left untouched.
     */
    template <class S>
    V8_WARN_UNUSED_RESULT V8_INLINE bool ToLocal(Local<S>* out) const {
      out->val_ = IsEmpty() ? nullptr : this->val_;
      return !IsEmpty();
    }
  
    /**
     * Converts this MaybeLocal<> to a Local<>. If this MaybeLocal<> is empty,
     * V8 will crash the process.
     */
    V8_INLINE Local<T> ToLocalChecked();
  
    /**
     * Converts this MaybeLocal<> to a Local<>, using a default value if this
     * MaybeLocal<> is empty.
     */
    template <class S>
    V8_INLINE Local<S> FromMaybe(Local<S> default_value) const {
      return IsEmpty() ? default_value : Local<S>(val_);
    }
  
   private:
    T* val_;
  };
  
  /**
   * Eternal handles are set-once handles that live for the lifetime of the
   * isolate.
   */
  template <class T> class Eternal {
   public:
    V8_INLINE Eternal() : val_(nullptr) {}
    template <class S>
    V8_INLINE Eternal(Isolate* isolate, Local<S> handle) : val_(nullptr) {
      Set(isolate, handle);
    }
    // Can only be safely called if already set.
    V8_INLINE Local<T> Get(Isolate* isolate) const;
    V8_INLINE bool IsEmpty() const { return val_ == nullptr; }
    template<class S> V8_INLINE void Set(Isolate* isolate, Local<S> handle);
  
   private:
    T* val_;
  };
  
  
  static const int kInternalFieldsInWeakCallback = 2;
  static const int kEmbedderFieldsInWeakCallback = 2;
  
  template <typename T>
  class WeakCallbackInfo {
   public:
    typedef void (*Callback)(const WeakCallbackInfo<T>& data);
  
    WeakCallbackInfo(Isolate* isolate, T* parameter,
                     void* embedder_fields[kEmbedderFieldsInWeakCallback],
                     Callback* callback)
        : isolate_(isolate), parameter_(parameter), callback_(callback) {
      for (int i = 0; i < kEmbedderFieldsInWeakCallback; ++i) {
        embedder_fields_[i] = embedder_fields[i];
      }
    }
  
    V8_INLINE Isolate* GetIsolate() const { return isolate_; }
    V8_INLINE T* GetParameter() const { return parameter_; }
    V8_INLINE void* GetInternalField(int index) const;
  
    // When first called, the embedder MUST Reset() the Global which triggered the
    // callback. The Global itself is unusable for anything else. No v8 other api
    // calls may be called in the first callback. Should additional work be
    // required, the embedder must set a second pass callback, which will be
    // called after all the initial callbacks are processed.
    // Calling SetSecondPassCallback on the second pass will immediately crash.
    void SetSecondPassCallback(Callback callback) const { *callback_ = callback; }
  
   private:
    Isolate* isolate_;
    T* parameter_;
    Callback* callback_;
    void* embedder_fields_[kEmbedderFieldsInWeakCallback];
  };
  
  
  // kParameter will pass a void* parameter back to the callback, kInternalFields
  // will pass the first two internal fields back to the callback, kFinalizer
  // will pass a void* parameter back, but is invoked before the object is
  // actually collected, so it can be resurrected. In the last case, it is not
  // possible to request a second pass callback.
  enum class WeakCallbackType { kParameter, kInternalFields, kFinalizer };
  
  /**
   * An object reference that is independent of any handle scope.  Where
   * a Local handle only lives as long as the HandleScope in which it was
   * allocated, a PersistentBase handle remains valid until it is explicitly
   * disposed using Reset().
   *
   * A persistent handle contains a reference to a storage cell within
   * the V8 engine which holds an object value and which is updated by
   * the garbage collector whenever the object is moved.  A new storage
   * cell can be created using the constructor or PersistentBase::Reset and
   * existing handles can be disposed using PersistentBase::Reset.
   *
   */
  template <class T> class PersistentBase {
   public:
    /**
     * If non-empty, destroy the underlying storage cell
     * IsEmpty() will return true after this call.
     */
    V8_INLINE void Reset();
    /**
     * If non-empty, destroy the underlying storage cell
     * and create a new one with the contents of other if other is non empty
     */
    template <class S>
    V8_INLINE void Reset(Isolate* isolate, const Local<S>& other);
  
    /**
     * If non-empty, destroy the underlying storage cell
     * and create a new one with the contents of other if other is non empty
     */
    template <class S>
    V8_INLINE void Reset(Isolate* isolate, const PersistentBase<S>& other);
  
    V8_INLINE bool IsEmpty() const { return val_ == nullptr; }
    V8_INLINE void Empty() { val_ = 0; }
  
    V8_INLINE Local<T> Get(Isolate* isolate) const {
      return Local<T>::New(isolate, *this);
    }
  
    template <class S>
    V8_INLINE bool operator==(const PersistentBase<S>& that) const {
      internal::Address* a = reinterpret_cast<internal::Address*>(this->val_);
      internal::Address* b = reinterpret_cast<internal::Address*>(that.val_);
      if (a == nullptr) return b == nullptr;
      if (b == nullptr) return false;
      return *a == *b;
    }
  
    template <class S>
    V8_INLINE bool operator==(const Local<S>& that) const {
      internal::Address* a = reinterpret_cast<internal::Address*>(this->val_);
      internal::Address* b = reinterpret_cast<internal::Address*>(that.val_);
      if (a == nullptr) return b == nullptr;
      if (b == nullptr) return false;
      return *a == *b;
    }
  
    template <class S>
    V8_INLINE bool operator!=(const PersistentBase<S>& that) const {
      return !operator==(that);
    }
  
    template <class S>
    V8_INLINE bool operator!=(const Local<S>& that) const {
      return !operator==(that);
    }
  
    /**
     *  Install a finalization callback on this object.
     *  NOTE: There is no guarantee as to *when* or even *if* the callback is
     *  invoked. The invocation is performed solely on a best effort basis.
     *  As always, GC-based finalization should *not* be relied upon for any
     *  critical form of resource management!
     */
    template <typename P>
    V8_INLINE void SetWeak(P* parameter,
                           typename WeakCallbackInfo<P>::Callback callback,
                           WeakCallbackType type);
  
    /**
     * Turns this handle into a weak phantom handle without finalization callback.
     * The handle will be reset automatically when the garbage collector detects
     * that the object is no longer reachable.
     * A related function Isolate::NumberOfPhantomHandleResetsSinceLastCall
     * returns how many phantom handles were reset by the garbage collector.
     */
    V8_INLINE void SetWeak();
  
    template<typename P>
    V8_INLINE P* ClearWeak();
  
    // TODO(dcarney): remove this.
    V8_INLINE void ClearWeak() { ClearWeak<void>(); }
  
    /**
     * Annotates the strong handle with the given label, which is then used by the
     * heap snapshot generator as a name of the edge from the root to the handle.
     * The function does not take ownership of the label and assumes that the
     * label is valid as long as the handle is valid.
     */
    V8_INLINE void AnnotateStrongRetainer(const char* label);
  
    /** Returns true if the handle's reference is weak.  */
    V8_INLINE bool IsWeak() const;
  
    /**
     * Assigns a wrapper class ID to the handle.
     */
    V8_INLINE void SetWrapperClassId(uint16_t class_id);
  
    /**
     * Returns the class ID previously assigned to this handle or 0 if no class ID
     * was previously assigned.
     */
    V8_INLINE uint16_t WrapperClassId() const;
  
    PersistentBase(const PersistentBase& other) = delete;  // NOLINT
    void operator=(const PersistentBase&) = delete;
  
   private:
    friend class Isolate;
    friend class Utils;
    template<class F> friend class Local;
    template<class F1, class F2> friend class Persistent;
    template <class F>
    friend class Global;
    template<class F> friend class PersistentBase;
    template<class F> friend class ReturnValue;
    template <class F1, class F2, class F3>
    friend class PersistentValueMapBase;
    template<class F1, class F2> friend class PersistentValueVector;
    friend class Object;
  
    explicit V8_INLINE PersistentBase(T* val) : val_(val) {}
    V8_INLINE static T* New(Isolate* isolate, T* that);
  
    T* val_;
  };
  
  
  /**
   * Default traits for Persistent. This class does not allow
   * use of the copy constructor or assignment operator.
   * At present kResetInDestructor is not set, but that will change in a future
   * version.
   */
  template<class T>
  class NonCopyablePersistentTraits {
   public:
    typedef Persistent<T, NonCopyablePersistentTraits<T> > NonCopyablePersistent;
    static const bool kResetInDestructor = false;
    template<class S, class M>
    V8_INLINE static void Copy(const Persistent<S, M>& source,
                               NonCopyablePersistent* dest) {
      Uncompilable<Object>();
    }
    // TODO(dcarney): come up with a good compile error here.
    template<class O> V8_INLINE static void Uncompilable() {
      TYPE_CHECK(O, Primitive);
    }
  };
  
  
  /**
   * Helper class traits to allow copying and assignment of Persistent.
   * This will clone the contents of storage cell, but not any of the flags, etc.
   */
  template<class T>
  struct CopyablePersistentTraits {
    typedef Persistent<T, CopyablePersistentTraits<T> > CopyablePersistent;
    static const bool kResetInDestructor = true;
    template<class S, class M>
    static V8_INLINE void Copy(const Persistent<S, M>& source,
                               CopyablePersistent* dest) {
      // do nothing, just allow copy
    }
  };
  
  
  /**
   * A PersistentBase which allows copy and assignment.
   *
   * Copy, assignment and destructor behavior is controlled by the traits
   * class M.
   *
   * Note: Persistent class hierarchy is subject to future changes.
   */
  template <class T, class M> class Persistent : public PersistentBase<T> {
   public:
    /**
     * A Persistent with no storage cell.
     */
    V8_INLINE Persistent() : PersistentBase<T>(nullptr) {}
    /**
     * Construct a Persistent from a Local.
     * When the Local is non-empty, a new storage cell is created
     * pointing to the same object, and no flags are set.
     */
    template <class S>
    V8_INLINE Persistent(Isolate* isolate, Local<S> that)
        : PersistentBase<T>(PersistentBase<T>::New(isolate, *that)) {
      TYPE_CHECK(T, S);
    }
    /**
     * Construct a Persistent from a Persistent.
     * When the Persistent is non-empty, a new storage cell is created
     * pointing to the same object, and no flags are set.
     */
    template <class S, class M2>
    V8_INLINE Persistent(Isolate* isolate, const Persistent<S, M2>& that)
      : PersistentBase<T>(PersistentBase<T>::New(isolate, *that)) {
      TYPE_CHECK(T, S);
    }
    /**
     * The copy constructors and assignment operator create a Persistent
     * exactly as the Persistent constructor, but the Copy function from the
     * traits class is called, allowing the setting of flags based on the
     * copied Persistent.
     */
    V8_INLINE Persistent(const Persistent& that) : PersistentBase<T>(nullptr) {
      Copy(that);
    }
    template <class S, class M2>
    V8_INLINE Persistent(const Persistent<S, M2>& that) : PersistentBase<T>(0) {
      Copy(that);
    }
    V8_INLINE Persistent& operator=(const Persistent& that) {
      Copy(that);
      return *this;
    }
    template <class S, class M2>
    V8_INLINE Persistent& operator=(const Persistent<S, M2>& that) { // NOLINT
      Copy(that);
      return *this;
    }
    /**
     * The destructor will dispose the Persistent based on the
     * kResetInDestructor flags in the traits class.  Since not calling dispose
     * can result in a memory leak, it is recommended to always set this flag.
     */
    V8_INLINE ~Persistent() {
      if (M::kResetInDestructor) this->Reset();
    }
  
    // TODO(dcarney): this is pretty useless, fix or remove
    template <class S>
    V8_INLINE static Persistent<T>& Cast(const Persistent<S>& that) {  // NOLINT
  #ifdef V8_ENABLE_CHECKS
      // If we're going to perform the type check then we have to check
      // that the handle isn't empty before doing the checked cast.
      if (!that.IsEmpty()) T::Cast(*that);
  #endif
      return reinterpret_cast<Persistent<T>&>(const_cast<Persistent<S>&>(that));
    }
  
    // TODO(dcarney): this is pretty useless, fix or remove
    template <class S>
    V8_INLINE Persistent<S>& As() const {  // NOLINT
      return Persistent<S>::Cast(*this);
    }
  
   private:
    friend class Isolate;
    friend class Utils;
    template<class F> friend class Local;
    template<class F1, class F2> friend class Persistent;
    template<class F> friend class ReturnValue;
  
    explicit V8_INLINE Persistent(T* that) : PersistentBase<T>(that) {}
    V8_INLINE T* operator*() const { return this->val_; }
    template<class S, class M2>
    V8_INLINE void Copy(const Persistent<S, M2>& that);
  };
  
  
  /**
   * A PersistentBase which has move semantics.
   *
   * Note: Persistent class hierarchy is subject to future changes.
   */
  template <class T>
  class Global : public PersistentBase<T> {
   public:
    /**
     * A Global with no storage cell.
     */
    V8_INLINE Global() : PersistentBase<T>(nullptr) {}
  
    /**
     * Construct a Global from a Local.
     * When the Local is non-empty, a new storage cell is created
     * pointing to the same object, and no flags are set.
     */
    template <class S>
    V8_INLINE Global(Isolate* isolate, Local<S> that)
        : PersistentBase<T>(PersistentBase<T>::New(isolate, *that)) {
      TYPE_CHECK(T, S);
    }
  
    /**
     * Construct a Global from a PersistentBase.
     * When the Persistent is non-empty, a new storage cell is created
     * pointing to the same object, and no flags are set.
     */
    template <class S>
    V8_INLINE Global(Isolate* isolate, const PersistentBase<S>& that)
        : PersistentBase<T>(PersistentBase<T>::New(isolate, that.val_)) {
      TYPE_CHECK(T, S);
    }
  
    /**
     * Move constructor.
     */
    V8_INLINE Global(Global&& other);
  
    V8_INLINE ~Global() { this->Reset(); }
  
    /**
     * Move via assignment.
     */
    template <class S>
    V8_INLINE Global& operator=(Global<S>&& rhs);
  
    /**
     * Pass allows returning uniques from functions, etc.
     */
    Global Pass() { return static_cast<Global&&>(*this); }  // NOLINT
  
    /*
     * For compatibility with Chromium's base::Bind (base::Passed).
     */
    typedef void MoveOnlyTypeForCPP03;
  
    Global(const Global&) = delete;
    void operator=(const Global&) = delete;
  
   private:
    template <class F>
    friend class ReturnValue;
    V8_INLINE T* operator*() const { return this->val_; }
  };
  
  
  // UniquePersistent is an alias for Global for historical reason.
  template <class T>
  using UniquePersistent = Global<T>;
  
  /**
   * A traced handle with move semantics, similar to std::unique_ptr. The handle
   * is to be used together with |v8::EmbedderHeapTracer| and specifies edges from
   * the embedder into V8's heap.
   *
   * The exact semantics are:
   * - Tracing garbage collections use |v8::EmbedderHeapTracer|.
   * - Non-tracing garbage collections refer to
   *   |v8::EmbedderHeapTracer::IsRootForNonTracingGC()| whether the handle should
   *   be treated as root or not.
   */
  template <typename T>
  class V8_EXPORT TracedGlobal {
   public:
    /**
     * An empty TracedGlobal without storage cell.
     */
    TracedGlobal() = default;
    ~TracedGlobal() { Reset(); }
  
    /**
     * Construct a TracedGlobal from a Local.
     *
     * When the Local is non-empty, a new storage cell is created
     * pointing to the same object.
     */
    template <class S>
    TracedGlobal(Isolate* isolate, Local<S> that)
        : val_(New(isolate, *that, &val_)) {
      TYPE_CHECK(T, S);
    }
  
    /**
     * Move constructor initializing TracedGlobal from an existing one.
     */
    V8_INLINE TracedGlobal(TracedGlobal&& other);
  
    /**
     * Move assignment operator initializing TracedGlobal from an existing one.
     */
    template <class S>
    V8_INLINE TracedGlobal& operator=(TracedGlobal<S>&& rhs);
  
    /**
     * TracedGlobal only supports move semantics and forbids copying.
     */
    TracedGlobal(const TracedGlobal&) = delete;
    void operator=(const TracedGlobal&) = delete;
  
    /**
     * Returns true if this TracedGlobal is empty, i.e., has not been assigned an
     * object.
     */
    bool IsEmpty() const { return val_ == nullptr; }
  
    /**
     * If non-empty, destroy the underlying storage cell. |IsEmpty| will return
     * true after this call.
     */
    V8_INLINE void Reset();
  
    /**
     * If non-empty, destroy the underlying storage cell and create a new one with
     * the contents of other if other is non empty
     */
    template <class S>
    V8_INLINE void Reset(Isolate* isolate, const Local<S>& other);
  
    /**
     * Construct a Local<T> from this handle.
     */
    Local<T> Get(Isolate* isolate) const { return Local<T>::New(isolate, *this); }
  
    template <class S>
    V8_INLINE TracedGlobal<S>& As() const {
      return reinterpret_cast<TracedGlobal<S>&>(
          const_cast<TracedGlobal<T>&>(*this));
    }
  
    template <class S>
    V8_INLINE bool operator==(const TracedGlobal<S>& that) const {
      internal::Address* a = reinterpret_cast<internal::Address*>(this->val_);
      internal::Address* b = reinterpret_cast<internal::Address*>(that.val_);
      if (a == nullptr) return b == nullptr;
      if (b == nullptr) return false;
      return *a == *b;
    }
  
    template <class S>
    V8_INLINE bool operator==(const Local<S>& that) const {
      internal::Address* a = reinterpret_cast<internal::Address*>(this->val_);
      internal::Address* b = reinterpret_cast<internal::Address*>(that.val_);
      if (a == nullptr) return b == nullptr;
      if (b == nullptr) return false;
      return *a == *b;
    }
  
    template <class S>
    V8_INLINE bool operator!=(const TracedGlobal<S>& that) const {
      return !operator==(that);
    }
  
    template <class S>
    V8_INLINE bool operator!=(const Local<S>& that) const {
      return !operator==(that);
    }
  
    /**
     * Assigns a wrapper class ID to the handle.
     */
    V8_INLINE void SetWrapperClassId(uint16_t class_id);
  
    /**
     * Returns the class ID previously assigned to this handle or 0 if no class ID
     * was previously assigned.
     */
    V8_INLINE uint16_t WrapperClassId() const;
  
    /**
     * Adds a finalization callback to the handle. The type of this callback is
     * similar to WeakCallbackType::kInternalFields, i.e., it will pass the
     * parameter and the first two internal fields of the object.
     *
     * The callback is then supposed to reset the handle in the callback. No
     * further V8 API may be called in this callback. In case additional work
     * involving V8 needs to be done, a second callback can be scheduled using
     * WeakCallbackInfo<void>::SetSecondPassCallback.
     */
    V8_INLINE void SetFinalizationCallback(
        void* parameter, WeakCallbackInfo<void>::Callback callback);
  
   private:
    V8_INLINE static T* New(Isolate* isolate, T* that, T** slot);
  
    T* operator*() const { return this->val_; }
  
    T* val_ = nullptr;
  
    friend class EmbedderHeapTracer;
    template <typename F>
    friend class Local;
    friend class Object;
    template <typename F>
    friend class ReturnValue;
  };
  
   /**
   * A stack-allocated class that governs a number of local handles.
   * After a handle scope has been created, all local handles will be
   * allocated within that handle scope until either the handle scope is
   * deleted or another handle scope is created.  If there is already a
   * handle scope and a new one is created, all allocations will take
   * place in the new handle scope until it is deleted.  After that,
   * new handles will again be allocated in the original handle scope.
   *
   * After the handle scope of a local handle has been deleted the
   * garbage collector will no longer track the object stored in the
   * handle and may deallocate it.  The behavior of accessing a handle
   * for which the handle scope has been deleted is undefined.
   */
  class V8_EXPORT HandleScope {
   public:
    explicit HandleScope(Isolate* isolate);
  
    ~HandleScope();
  
    /**
     * Counts the number of allocated handles.
     */
    static int NumberOfHandles(Isolate* isolate);
  
    V8_INLINE Isolate* GetIsolate() const {
      return reinterpret_cast<Isolate*>(isolate_);
    }
  
    HandleScope(const HandleScope&) = delete;
    void operator=(const HandleScope&) = delete;
  
   protected:
    V8_INLINE HandleScope() = default;
  
    void Initialize(Isolate* isolate);
  
    static internal::Address* CreateHandle(internal::Isolate* isolate,
                                           internal::Address value);
  
   private:
    // Declaring operator new and delete as deleted is not spec compliant.
    // Therefore declare them private instead to disable dynamic alloc
    void* operator new(size_t size);
    void* operator new[](size_t size);
    void operator delete(void*, size_t);
    void operator delete[](void*, size_t);
  
    internal::Isolate* isolate_;
    internal::Address* prev_next_;
    internal::Address* prev_limit_;
  
    // Local::New uses CreateHandle with an Isolate* parameter.
    template<class F> friend class Local;
  
    // Object::GetInternalField and Context::GetEmbedderData use CreateHandle with
    // a HeapObject in their shortcuts.
    friend class Object;
    friend class Context;
  };
  
  
  /**
   * A HandleScope which first allocates a handle in the current scope
   * which will be later filled with the escape value.
   */
  class V8_EXPORT EscapableHandleScope : public HandleScope {
   public:
    explicit EscapableHandleScope(Isolate* isolate);
    V8_INLINE ~EscapableHandleScope() = default;
  
    /**
     * Pushes the value into the previous scope and returns a handle to it.
     * Cannot be called twice.
     */
    template <class T>
    V8_INLINE Local<T> Escape(Local<T> value) {
      internal::Address* slot =
          Escape(reinterpret_cast<internal::Address*>(*value));
      return Local<T>(reinterpret_cast<T*>(slot));
    }
  
    template <class T>
    V8_INLINE MaybeLocal<T> EscapeMaybe(MaybeLocal<T> value) {
      return Escape(value.FromMaybe(Local<T>()));
    }
  
    EscapableHandleScope(const EscapableHandleScope&) = delete;
    void operator=(const EscapableHandleScope&) = delete;
  
   private:
    // Declaring operator new and delete as deleted is not spec compliant.
    // Therefore declare them private instead to disable dynamic alloc
    void* operator new(size_t size);
    void* operator new[](size_t size);
    void operator delete(void*, size_t);
    void operator delete[](void*, size_t);
  
    internal::Address* Escape(internal::Address* escape_value);
    internal::Address* escape_slot_;
  };
  
  /**
   * A SealHandleScope acts like a handle scope in which no handle allocations
   * are allowed. It can be useful for debugging handle leaks.
   * Handles can be allocated within inner normal HandleScopes.
   */
  class V8_EXPORT SealHandleScope {
   public:
    explicit SealHandleScope(Isolate* isolate);
    ~SealHandleScope();
  
    SealHandleScope(const SealHandleScope&) = delete;
    void operator=(const SealHandleScope&) = delete;
  
   private:
    // Declaring operator new and delete as deleted is not spec compliant.
    // Therefore declare them private instead to disable dynamic alloc
    void* operator new(size_t size);
    void* operator new[](size_t size);
    void operator delete(void*, size_t);
    void operator delete[](void*, size_t);
  
    internal::Isolate* const isolate_;
    internal::Address* prev_limit_;
    int prev_sealed_level_;
  };
  
  
  // --- Special objects ---
  
  
  /**
   * The superclass of values and API object templates.
   */
  class V8_EXPORT Data {
   private:
    Data();
  };
  
  /**
   * A container type that holds relevant metadata for module loading.
   *
   * This is passed back to the embedder as part of
   * HostImportModuleDynamicallyCallback for module loading.
   */
  class V8_EXPORT ScriptOrModule {
   public:
    /**
     * The name that was passed by the embedder as ResourceName to the
     * ScriptOrigin. This can be either a v8::String or v8::Undefined.
     */
    Local<Value> GetResourceName();
  
    /**
     * The options that were passed by the embedder as HostDefinedOptions to
     * the ScriptOrigin.
     */
    Local<PrimitiveArray> GetHostDefinedOptions();
  };
  
  /**
   * An array to hold Primitive values. This is used by the embedder to
   * pass host defined options to the ScriptOptions during compilation.
   *
   * This is passed back to the embedder as part of
   * HostImportModuleDynamicallyCallback for module loading.
   *
   */
  class V8_EXPORT PrimitiveArray {
   public:
    static Local<PrimitiveArray> New(Isolate* isolate, int length);
    int Length() const;
    void Set(Isolate* isolate, int index, Local<Primitive> item);
    Local<Primitive> Get(Isolate* isolate, int index);
  };
  
  /**
   * The optional attributes of ScriptOrigin.
   */
  class ScriptOriginOptions {
   public:
    V8_INLINE ScriptOriginOptions(bool is_shared_cross_origin = false,
                                  bool is_opaque = false, bool is_wasm = false,
                                  bool is_module = false)
        : flags_((is_shared_cross_origin ? kIsSharedCrossOrigin : 0) |
                 (is_wasm ? kIsWasm : 0) | (is_opaque ? kIsOpaque : 0) |
                 (is_module ? kIsModule : 0)) {}
    V8_INLINE ScriptOriginOptions(int flags)
        : flags_(flags &
                 (kIsSharedCrossOrigin | kIsOpaque | kIsWasm | kIsModule)) {}
  
    bool IsSharedCrossOrigin() const {
      return (flags_ & kIsSharedCrossOrigin) != 0;
    }
    bool IsOpaque() const { return (flags_ & kIsOpaque) != 0; }
    bool IsWasm() const { return (flags_ & kIsWasm) != 0; }
    bool IsModule() const { return (flags_ & kIsModule) != 0; }
  
    int Flags() const { return flags_; }
  
   private:
    enum {
      kIsSharedCrossOrigin = 1,
      kIsOpaque = 1 << 1,
      kIsWasm = 1 << 2,
      kIsModule = 1 << 3
    };
    const int flags_;
  };
  
  /**
   * The origin, within a file, of a script.
   */
  class ScriptOrigin {
   public:
    V8_INLINE ScriptOrigin(
        Local<Value> resource_name,
        Local<Integer> resource_line_offset = Local<Integer>(),
        Local<Integer> resource_column_offset = Local<Integer>(),
        Local<Boolean> resource_is_shared_cross_origin = Local<Boolean>(),
        Local<Integer> script_id = Local<Integer>(),
        Local<Value> source_map_url = Local<Value>(),
        Local<Boolean> resource_is_opaque = Local<Boolean>(),
        Local<Boolean> is_wasm = Local<Boolean>(),
        Local<Boolean> is_module = Local<Boolean>(),
        Local<PrimitiveArray> host_defined_options = Local<PrimitiveArray>());
  
    V8_INLINE Local<Value> ResourceName() const;
    V8_INLINE Local<Integer> ResourceLineOffset() const;
    V8_INLINE Local<Integer> ResourceColumnOffset() const;
    V8_INLINE Local<Integer> ScriptID() const;
    V8_INLINE Local<Value> SourceMapUrl() const;
    V8_INLINE Local<PrimitiveArray> HostDefinedOptions() const;
    V8_INLINE ScriptOriginOptions Options() const { return options_; }
  
   private:
    Local<Value> resource_name_;
    Local<Integer> resource_line_offset_;
    Local<Integer> resource_column_offset_;
    ScriptOriginOptions options_;
    Local<Integer> script_id_;
    Local<Value> source_map_url_;
    Local<PrimitiveArray> host_defined_options_;
  };
  
  /**
   * A compiled JavaScript script, not yet tied to a Context.
   */
  class V8_EXPORT UnboundScript {
   public:
    /**
     * Binds the script to the currently entered context.
     */
    Local<Script> BindToCurrentContext();
  
    int GetId();
    Local<Value> GetScriptName();
  
    /**
     * Data read from magic sourceURL comments.
     */
    Local<Value> GetSourceURL();
    /**
     * Data read from magic sourceMappingURL comments.
     */
    Local<Value> GetSourceMappingURL();
  
    /**
     * Returns zero based line number of the code_pos location in the script.
     * -1 will be returned if no information available.
     */
    int GetLineNumber(int code_pos);
  
    static const int kNoScriptId = 0;
  };
  
  /**
   * A compiled JavaScript module, not yet tied to a Context.
   */
  class V8_EXPORT UnboundModuleScript {
    // Only used as a container for code caching.
  };
  
  /**
   * A location in JavaScript source.
   */
  class V8_EXPORT Location {
   public:
    int GetLineNumber() { return line_number_; }
    int GetColumnNumber() { return column_number_; }
  
    Location(int line_number, int column_number)
        : line_number_(line_number), column_number_(column_number) {}
  
   private:
    int line_number_;
    int column_number_;
  };
  
  /**
   * A compiled JavaScript module.
   */
  class V8_EXPORT Module {
   public:
    /**
     * The different states a module can be in.
     *
     * This corresponds to the states used in ECMAScript except that "evaluated"
     * is split into kEvaluated and kErrored, indicating success and failure,
     * respectively.
     */
    enum Status {
      kUninstantiated,
      kInstantiating,
      kInstantiated,
      kEvaluating,
      kEvaluated,
      kErrored
    };
  
    /**
     * Returns the module's current status.
     */
    Status GetStatus() const;
  
    /**
     * For a module in kErrored status, this returns the corresponding exception.
     */
    Local<Value> GetException() const;
  
    /**
     * Returns the number of modules requested by this module.
     */
    int GetModuleRequestsLength() const;
  
    /**
     * Returns the ith module specifier in this module.
     * i must be < GetModuleRequestsLength() and >= 0.
     */
    Local<String> GetModuleRequest(int i) const;
  
    /**
     * Returns the source location (line number and column number) of the ith
     * module specifier's first occurrence in this module.
     */
    Location GetModuleRequestLocation(int i) const;
  
    /**
     * Returns the identity hash for this object.
     */
    int GetIdentityHash() const;
  
    typedef MaybeLocal<Module> (*ResolveCallback)(Local<Context> context,
                                                  Local<String> specifier,
                                                  Local<Module> referrer);
  
    /**
     * Instantiates the module and its dependencies.
     *
     * Returns an empty Maybe<bool> if an exception occurred during
     * instantiation. (In the case where the callback throws an exception, that
     * exception is propagated.)
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> InstantiateModule(Local<Context> context,
                                                        ResolveCallback callback);
  
    /**
     * Evaluates the module and its dependencies.
     *
     * If status is kInstantiated, run the module's code. On success, set status
     * to kEvaluated and return the completion value; on failure, set status to
     * kErrored and propagate the thrown exception (which is then also available
     * via |GetException|).
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> Evaluate(Local<Context> context);
  
    /**
     * Returns the namespace object of this module.
     *
     * The module's status must be at least kInstantiated.
     */
    Local<Value> GetModuleNamespace();
  
    /**
     * Returns the corresponding context-unbound module script.
     *
     * The module must be unevaluated, i.e. its status must not be kEvaluating,
     * kEvaluated or kErrored.
     */
    Local<UnboundModuleScript> GetUnboundModuleScript();
  };
  
  /**
   * A compiled JavaScript script, tied to a Context which was active when the
   * script was compiled.
   */
  class V8_EXPORT Script {
   public:
    /**
     * A shorthand for ScriptCompiler::Compile().
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<Script> Compile(
        Local<Context> context, Local<String> source,
        ScriptOrigin* origin = nullptr);
  
    /**
     * Runs the script returning the resulting value. It will be run in the
     * context in which it was created (ScriptCompiler::CompileBound or
     * UnboundScript::BindToCurrentContext()).
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> Run(Local<Context> context);
  
    /**
     * Returns the corresponding context-unbound script.
     */
    Local<UnboundScript> GetUnboundScript();
  };
  
  
  /**
   * For compiling scripts.
   */
  class V8_EXPORT ScriptCompiler {
   public:
    /**
     * Compilation data that the embedder can cache and pass back to speed up
     * future compilations. The data is produced if the CompilerOptions passed to
     * the compilation functions in ScriptCompiler contains produce_data_to_cache
     * = true. The data to cache can then can be retrieved from
     * UnboundScript.
     */
    struct V8_EXPORT CachedData {
      enum BufferPolicy {
        BufferNotOwned,
        BufferOwned
      };
  
      CachedData()
          : data(nullptr),
            length(0),
            rejected(false),
            buffer_policy(BufferNotOwned) {}
  
      // If buffer_policy is BufferNotOwned, the caller keeps the ownership of
      // data and guarantees that it stays alive until the CachedData object is
      // destroyed. If the policy is BufferOwned, the given data will be deleted
      // (with delete[]) when the CachedData object is destroyed.
      CachedData(const uint8_t* data, int length,
                 BufferPolicy buffer_policy = BufferNotOwned);
      ~CachedData();
      // TODO(marja): Async compilation; add constructors which take a callback
      // which will be called when V8 no longer needs the data.
      const uint8_t* data;
      int length;
      bool rejected;
      BufferPolicy buffer_policy;
  
      // Prevent copying.
      CachedData(const CachedData&) = delete;
      CachedData& operator=(const CachedData&) = delete;
    };
  
    /**
     * Source code which can be then compiled to a UnboundScript or Script.
     */
    class Source {
     public:
      // Source takes ownership of CachedData.
      V8_INLINE Source(Local<String> source_string, const ScriptOrigin& origin,
                       CachedData* cached_data = nullptr);
      V8_INLINE Source(Local<String> source_string,
                       CachedData* cached_data = nullptr);
      V8_INLINE ~Source();
  
      // Ownership of the CachedData or its buffers is *not* transferred to the
      // caller. The CachedData object is alive as long as the Source object is
      // alive.
      V8_INLINE const CachedData* GetCachedData() const;
  
      V8_INLINE const ScriptOriginOptions& GetResourceOptions() const;
  
      // Prevent copying.
      Source(const Source&) = delete;
      Source& operator=(const Source&) = delete;
  
     private:
      friend class ScriptCompiler;
  
      Local<String> source_string;
  
      // Origin information
      Local<Value> resource_name;
      Local<Integer> resource_line_offset;
      Local<Integer> resource_column_offset;
      ScriptOriginOptions resource_options;
      Local<Value> source_map_url;
      Local<PrimitiveArray> host_defined_options;
  
      // Cached data from previous compilation (if a kConsume*Cache flag is
      // set), or hold newly generated cache data (kProduce*Cache flags) are
      // set when calling a compile method.
      CachedData* cached_data;
    };
  
    /**
     * For streaming incomplete script data to V8. The embedder should implement a
     * subclass of this class.
     */
    class V8_EXPORT ExternalSourceStream {
     public:
      virtual ~ExternalSourceStream() = default;
  
      /**
       * V8 calls this to request the next chunk of data from the embedder. This
       * function will be called on a background thread, so it's OK to block and
       * wait for the data, if the embedder doesn't have data yet. Returns the
       * length of the data returned. When the data ends, GetMoreData should
       * return 0. Caller takes ownership of the data.
       *
       * When streaming UTF-8 data, V8 handles multi-byte characters split between
       * two data chunks, but doesn't handle multi-byte characters split between
       * more than two data chunks. The embedder can avoid this problem by always
       * returning at least 2 bytes of data.
       *
       * When streaming UTF-16 data, V8 does not handle characters split between
       * two data chunks. The embedder has to make sure that chunks have an even
       * length.
       *
       * If the embedder wants to cancel the streaming, they should make the next
       * GetMoreData call return 0. V8 will interpret it as end of data (and most
       * probably, parsing will fail). The streaming task will return as soon as
       * V8 has parsed the data it received so far.
       */
      virtual size_t GetMoreData(const uint8_t** src) = 0;
  
      /**
       * V8 calls this method to set a 'bookmark' at the current position in
       * the source stream, for the purpose of (maybe) later calling
       * ResetToBookmark. If ResetToBookmark is called later, then subsequent
       * calls to GetMoreData should return the same data as they did when
       * SetBookmark was called earlier.
       *
       * The embedder may return 'false' to indicate it cannot provide this
       * functionality.
       */
      virtual bool SetBookmark();
  
      /**
       * V8 calls this to return to a previously set bookmark.
       */
      virtual void ResetToBookmark();
    };
  
    /**
     * Source code which can be streamed into V8 in pieces. It will be parsed
     * while streaming and compiled after parsing has completed. StreamedSource
     * must be kept alive while the streaming task is run (see ScriptStreamingTask
     * below).
     */
    class V8_EXPORT StreamedSource {
     public:
      enum Encoding { ONE_BYTE, TWO_BYTE, UTF8 };
  
      V8_DEPRECATE_SOON(
          "This class takes ownership of source_stream, so use the constructor "
          "taking a unique_ptr to make these semantics clearer",
          StreamedSource(ExternalSourceStream* source_stream, Encoding encoding));
      StreamedSource(std::unique_ptr<ExternalSourceStream> source_stream,
                     Encoding encoding);
      ~StreamedSource();
  
      internal::ScriptStreamingData* impl() const { return impl_.get(); }
  
      // Prevent copying.
      StreamedSource(const StreamedSource&) = delete;
      StreamedSource& operator=(const StreamedSource&) = delete;
  
     private:
      std::unique_ptr<internal::ScriptStreamingData> impl_;
    };
  
    /**
     * A streaming task which the embedder must run on a background thread to
     * stream scripts into V8. Returned by ScriptCompiler::StartStreamingScript.
     */
    class V8_EXPORT ScriptStreamingTask final {
     public:
      void Run();
  
     private:
      friend class ScriptCompiler;
  
      explicit ScriptStreamingTask(internal::ScriptStreamingData* data)
          : data_(data) {}
  
      internal::ScriptStreamingData* data_;
    };
  
    enum CompileOptions {
      kNoCompileOptions = 0,
      kConsumeCodeCache,
      kEagerCompile
    };
  
    /**
     * The reason for which we are not requesting or providing a code cache.
     */
    enum NoCacheReason {
      kNoCacheNoReason = 0,
      kNoCacheBecauseCachingDisabled,
      kNoCacheBecauseNoResource,
      kNoCacheBecauseInlineScript,
      kNoCacheBecauseModule,
      kNoCacheBecauseStreamingSource,
      kNoCacheBecauseInspector,
      kNoCacheBecauseScriptTooSmall,
      kNoCacheBecauseCacheTooCold,
      kNoCacheBecauseV8Extension,
      kNoCacheBecauseExtensionModule,
      kNoCacheBecausePacScript,
      kNoCacheBecauseInDocumentWrite,
      kNoCacheBecauseResourceWithNoCacheHandler,
      kNoCacheBecauseDeferredProduceCodeCache
    };
  
    /**
     * Compiles the specified script (context-independent).
     * Cached data as part of the source object can be optionally produced to be
     * consumed later to speed up compilation of identical source scripts.
     *
     * Note that when producing cached data, the source must point to NULL for
     * cached data. When consuming cached data, the cached data must have been
     * produced by the same version of V8.
     *
     * \param source Script source code.
     * \return Compiled script object (context independent; for running it must be
     *   bound to a context).
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<UnboundScript> CompileUnboundScript(
        Isolate* isolate, Source* source,
        CompileOptions options = kNoCompileOptions,
        NoCacheReason no_cache_reason = kNoCacheNoReason);
  
    /**
     * Compiles the specified script (bound to current context).
     *
     * \param source Script source code.
     * \param pre_data Pre-parsing data, as obtained by ScriptData::PreCompile()
     *   using pre_data speeds compilation if it's done multiple times.
     *   Owned by caller, no references are kept when this function returns.
     * \return Compiled script object, bound to the context that was active
     *   when this function was called. When run it will always use this
     *   context.
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<Script> Compile(
        Local<Context> context, Source* source,
        CompileOptions options = kNoCompileOptions,
        NoCacheReason no_cache_reason = kNoCacheNoReason);
  
    /**
     * Returns a task which streams script data into V8, or NULL if the script
     * cannot be streamed. The user is responsible for running the task on a
     * background thread and deleting it. When ran, the task starts parsing the
     * script, and it will request data from the StreamedSource as needed. When
     * ScriptStreamingTask::Run exits, all data has been streamed and the script
     * can be compiled (see Compile below).
     *
     * This API allows to start the streaming with as little data as possible, and
     * the remaining data (for example, the ScriptOrigin) is passed to Compile.
     */
    static ScriptStreamingTask* StartStreamingScript(
        Isolate* isolate, StreamedSource* source,
        CompileOptions options = kNoCompileOptions);
  
    /**
     * Compiles a streamed script (bound to current context).
     *
     * This can only be called after the streaming has finished
     * (ScriptStreamingTask has been run). V8 doesn't construct the source string
     * during streaming, so the embedder needs to pass the full source here.
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<Script> Compile(
        Local<Context> context, StreamedSource* source,
        Local<String> full_source_string, const ScriptOrigin& origin);
  
    /**
     * Return a version tag for CachedData for the current V8 version & flags.
     *
     * This value is meant only for determining whether a previously generated
     * CachedData instance is still valid; the tag has no other meaing.
     *
     * Background: The data carried by CachedData may depend on the exact
     *   V8 version number or current compiler flags. This means that when
     *   persisting CachedData, the embedder must take care to not pass in
     *   data from another V8 version, or the same version with different
     *   features enabled.
     *
     *   The easiest way to do so is to clear the embedder's cache on any
     *   such change.
     *
     *   Alternatively, this tag can be stored alongside the cached data and
     *   compared when it is being used.
     */
    static uint32_t CachedDataVersionTag();
  
    /**
     * Compile an ES module, returning a Module that encapsulates
     * the compiled code.
     *
     * Corresponds to the ParseModule abstract operation in the
     * ECMAScript specification.
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<Module> CompileModule(
        Isolate* isolate, Source* source,
        CompileOptions options = kNoCompileOptions,
        NoCacheReason no_cache_reason = kNoCacheNoReason);
  
    /**
     * Compile a function for a given context. This is equivalent to running
     *
     * with (obj) {
     *   return function(args) { ... }
     * }
     *
     * It is possible to specify multiple context extensions (obj in the above
     * example).
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<Function> CompileFunctionInContext(
        Local<Context> context, Source* source, size_t arguments_count,
        Local<String> arguments[], size_t context_extension_count,
        Local<Object> context_extensions[],
        CompileOptions options = kNoCompileOptions,
        NoCacheReason no_cache_reason = kNoCacheNoReason);
  
    /**
     * Creates and returns code cache for the specified unbound_script.
     * This will return nullptr if the script cannot be serialized. The
     * CachedData returned by this function should be owned by the caller.
     */
    static CachedData* CreateCodeCache(Local<UnboundScript> unbound_script);
  
    /**
     * Creates and returns code cache for the specified unbound_module_script.
     * This will return nullptr if the script cannot be serialized. The
     * CachedData returned by this function should be owned by the caller.
     */
    static CachedData* CreateCodeCache(
        Local<UnboundModuleScript> unbound_module_script);
  
    /**
     * Creates and returns code cache for the specified function that was
     * previously produced by CompileFunctionInContext.
     * This will return nullptr if the script cannot be serialized. The
     * CachedData returned by this function should be owned by the caller.
     */
    static CachedData* CreateCodeCacheForFunction(Local<Function> function);
  
   private:
    static V8_WARN_UNUSED_RESULT MaybeLocal<UnboundScript> CompileUnboundInternal(
        Isolate* isolate, Source* source, CompileOptions options,
        NoCacheReason no_cache_reason);
  };
  
  
  /**
   * An error message.
   */
  class V8_EXPORT Message {
   public:
    Local<String> Get() const;
  
    /**
     * Return the isolate to which the Message belongs.
     */
    Isolate* GetIsolate() const;
  
    V8_WARN_UNUSED_RESULT MaybeLocal<String> GetSourceLine(
        Local<Context> context) const;
  
    /**
     * Returns the origin for the script from where the function causing the
     * error originates.
     */
    ScriptOrigin GetScriptOrigin() const;
  
    /**
     * Returns the resource name for the script from where the function causing
     * the error originates.
     */
    Local<Value> GetScriptResourceName() const;
  
    /**
     * Exception stack trace. By default stack traces are not captured for
     * uncaught exceptions. SetCaptureStackTraceForUncaughtExceptions allows
     * to change this option.
     */
    Local<StackTrace> GetStackTrace() const;
  
    /**
     * Returns the number, 1-based, of the line where the error occurred.
     */
    V8_WARN_UNUSED_RESULT Maybe<int> GetLineNumber(Local<Context> context) const;
  
    /**
     * Returns the index within the script of the first character where
     * the error occurred.
     */
    int GetStartPosition() const;
  
    /**
     * Returns the index within the script of the last character where
     * the error occurred.
     */
    int GetEndPosition() const;
  
    /**
     * Returns the error level of the message.
     */
    int ErrorLevel() const;
  
    /**
     * Returns the index within the line of the first character where
     * the error occurred.
     */
    int GetStartColumn() const;
    V8_WARN_UNUSED_RESULT Maybe<int> GetStartColumn(Local<Context> context) const;
  
    /**
     * Returns the index within the line of the last character where
     * the error occurred.
     */
    int GetEndColumn() const;
    V8_WARN_UNUSED_RESULT Maybe<int> GetEndColumn(Local<Context> context) const;
  
    /**
     * Passes on the value set by the embedder when it fed the script from which
     * this Message was generated to V8.
     */
    bool IsSharedCrossOrigin() const;
    bool IsOpaque() const;
  
    // TODO(1245381): Print to a string instead of on a FILE.
    static void PrintCurrentStackTrace(Isolate* isolate, FILE* out);
  
    static const int kNoLineNumberInfo = 0;
    static const int kNoColumnInfo = 0;
    static const int kNoScriptIdInfo = 0;
  };
  
  
  /**
   * Representation of a JavaScript stack trace. The information collected is a
   * snapshot of the execution stack and the information remains valid after
   * execution continues.
   */
  class V8_EXPORT StackTrace {
   public:
    /**
     * Flags that determine what information is placed captured for each
     * StackFrame when grabbing the current stack trace.
     * Note: these options are deprecated and we always collect all available
     * information (kDetailed).
     */
    enum StackTraceOptions {
      kLineNumber = 1,
      kColumnOffset = 1 << 1 | kLineNumber,
      kScriptName = 1 << 2,
      kFunctionName = 1 << 3,
      kIsEval = 1 << 4,
      kIsConstructor = 1 << 5,
      kScriptNameOrSourceURL = 1 << 6,
      kScriptId = 1 << 7,
      kExposeFramesAcrossSecurityOrigins = 1 << 8,
      kOverview = kLineNumber | kColumnOffset | kScriptName | kFunctionName,
      kDetailed = kOverview | kIsEval | kIsConstructor | kScriptNameOrSourceURL
    };
  
    /**
     * Returns a StackFrame at a particular index.
     */
    Local<StackFrame> GetFrame(Isolate* isolate, uint32_t index) const;
  
    /**
     * Returns the number of StackFrames.
     */
    int GetFrameCount() const;
  
    /**
     * Grab a snapshot of the current JavaScript execution stack.
     *
     * \param frame_limit The maximum number of stack frames we want to capture.
     * \param options Enumerates the set of things we will capture for each
     *   StackFrame.
     */
    static Local<StackTrace> CurrentStackTrace(
        Isolate* isolate, int frame_limit, StackTraceOptions options = kDetailed);
  };
  
  
  /**
   * A single JavaScript stack frame.
   */
  class V8_EXPORT StackFrame {
   public:
    /**
     * Returns the number, 1-based, of the line for the associate function call.
     * This method will return Message::kNoLineNumberInfo if it is unable to
     * retrieve the line number, or if kLineNumber was not passed as an option
     * when capturing the StackTrace.
     */
    int GetLineNumber() const;
  
    /**
     * Returns the 1-based column offset on the line for the associated function
     * call.
     * This method will return Message::kNoColumnInfo if it is unable to retrieve
     * the column number, or if kColumnOffset was not passed as an option when
     * capturing the StackTrace.
     */
    int GetColumn() const;
  
    /**
     * Returns the id of the script for the function for this StackFrame.
     * This method will return Message::kNoScriptIdInfo if it is unable to
     * retrieve the script id, or if kScriptId was not passed as an option when
     * capturing the StackTrace.
     */
    int GetScriptId() const;
  
    /**
     * Returns the name of the resource that contains the script for the
     * function for this StackFrame.
     */
    Local<String> GetScriptName() const;
  
    /**
     * Returns the name of the resource that contains the script for the
     * function for this StackFrame or sourceURL value if the script name
     * is undefined and its source ends with //# sourceURL=... string or
     * deprecated //@ sourceURL=... string.
     */
    Local<String> GetScriptNameOrSourceURL() const;
  
    /**
     * Returns the name of the function associated with this stack frame.
     */
    Local<String> GetFunctionName() const;
  
    /**
     * Returns whether or not the associated function is compiled via a call to
     * eval().
     */
    bool IsEval() const;
  
    /**
     * Returns whether or not the associated function is called as a
     * constructor via "new".
     */
    bool IsConstructor() const;
  
    /**
     * Returns whether or not the associated functions is defined in wasm.
     */
    bool IsWasm() const;
  
    /**
     * Returns whether or not the associated function is defined by the user.
     */
    bool IsUserJavaScript() const;
  };
  
  
  // A StateTag represents a possible state of the VM.
  enum StateTag {
    JS,
    GC,
    PARSER,
    BYTECODE_COMPILER,
    COMPILER,
    OTHER,
    EXTERNAL,
    IDLE
  };
  
  // A RegisterState represents the current state of registers used
  // by the sampling profiler API.
  struct RegisterState {
    RegisterState() : pc(nullptr), sp(nullptr), fp(nullptr), lr(nullptr) {}
    void* pc;  // Instruction pointer.
    void* sp;  // Stack pointer.
    void* fp;  // Frame pointer.
    void* lr;  // Link register (or nullptr on platforms without a link register).
  };
  
  // The output structure filled up by GetStackSample API function.
  struct SampleInfo {
    size_t frames_count;            // Number of frames collected.
    StateTag vm_state;              // Current VM state.
    void* external_callback_entry;  // External callback address if VM is
                                    // executing an external callback.
  };
  
  struct MemoryRange {
    const void* start = nullptr;
    size_t length_in_bytes = 0;
  };
  
  struct JSEntryStub {
    MemoryRange code;
  };
  
  struct UnwindState {
    MemoryRange code_range;
    MemoryRange embedded_code_range;
    JSEntryStub js_entry_stub;
  };
  
  /**
   * A JSON Parser and Stringifier.
   */
  class V8_EXPORT JSON {
   public:
    /**
     * Tries to parse the string |json_string| and returns it as value if
     * successful.
     *
     * \param the context in which to parse and create the value.
     * \param json_string The string to parse.
     * \return The corresponding value if successfully parsed.
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<Value> Parse(
        Local<Context> context, Local<String> json_string);
  
    /**
     * Tries to stringify the JSON-serializable object |json_object| and returns
     * it as string if successful.
     *
     * \param json_object The JSON-serializable object to stringify.
     * \return The corresponding string if successfully stringified.
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<String> Stringify(
        Local<Context> context, Local<Value> json_object,
        Local<String> gap = Local<String>());
  };
  
  /**
   * Value serialization compatible with the HTML structured clone algorithm.
   * The format is backward-compatible (i.e. safe to store to disk).
   */
  class V8_EXPORT ValueSerializer {
   public:
    class V8_EXPORT Delegate {
     public:
      virtual ~Delegate() = default;
  
      /**
       * Handles the case where a DataCloneError would be thrown in the structured
       * clone spec. Other V8 embedders may throw some other appropriate exception
       * type.
       */
      virtual void ThrowDataCloneError(Local<String> message) = 0;
  
      /**
       * The embedder overrides this method to write some kind of host object, if
       * possible. If not, a suitable exception should be thrown and
       * Nothing<bool>() returned.
       */
      virtual Maybe<bool> WriteHostObject(Isolate* isolate, Local<Object> object);
  
      /**
       * Called when the ValueSerializer is going to serialize a
       * SharedArrayBuffer object. The embedder must return an ID for the
       * object, using the same ID if this SharedArrayBuffer has already been
       * serialized in this buffer. When deserializing, this ID will be passed to
       * ValueDeserializer::GetSharedArrayBufferFromId as |clone_id|.
       *
       * If the object cannot be serialized, an
       * exception should be thrown and Nothing<uint32_t>() returned.
       */
      virtual Maybe<uint32_t> GetSharedArrayBufferId(
          Isolate* isolate, Local<SharedArrayBuffer> shared_array_buffer);
  
      virtual Maybe<uint32_t> GetWasmModuleTransferId(
          Isolate* isolate, Local<WasmModuleObject> module);
      /**
       * Allocates memory for the buffer of at least the size provided. The actual
       * size (which may be greater or equal) is written to |actual_size|. If no
       * buffer has been allocated yet, nullptr will be provided.
       *
       * If the memory cannot be allocated, nullptr should be returned.
       * |actual_size| will be ignored. It is assumed that |old_buffer| is still
       * valid in this case and has not been modified.
       *
       * The default implementation uses the stdlib's `realloc()` function.
       */
      virtual void* ReallocateBufferMemory(void* old_buffer, size_t size,
                                           size_t* actual_size);
  
      /**
       * Frees a buffer allocated with |ReallocateBufferMemory|.
       *
       * The default implementation uses the stdlib's `free()` function.
       */
      virtual void FreeBufferMemory(void* buffer);
    };
  
    explicit ValueSerializer(Isolate* isolate);
    ValueSerializer(Isolate* isolate, Delegate* delegate);
    ~ValueSerializer();
  
    /**
     * Writes out a header, which includes the format version.
     */
    void WriteHeader();
  
    /**
     * Serializes a JavaScript value into the buffer.
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> WriteValue(Local<Context> context,
                                                 Local<Value> value);
  
    /**
     * Returns the stored data (allocated using the delegate's
     * ReallocateBufferMemory) and its size. This serializer should not be used
     * once the buffer is released. The contents are undefined if a previous write
     * has failed. Ownership of the buffer is transferred to the caller.
     */
    V8_WARN_UNUSED_RESULT std::pair<uint8_t*, size_t> Release();
  
    /**
     * Marks an ArrayBuffer as havings its contents transferred out of band.
     * Pass the corresponding ArrayBuffer in the deserializing context to
     * ValueDeserializer::TransferArrayBuffer.
     */
    void TransferArrayBuffer(uint32_t transfer_id,
                             Local<ArrayBuffer> array_buffer);
  
  
    /**
     * Indicate whether to treat ArrayBufferView objects as host objects,
     * i.e. pass them to Delegate::WriteHostObject. This should not be
     * called when no Delegate was passed.
     *
     * The default is not to treat ArrayBufferViews as host objects.
     */
    void SetTreatArrayBufferViewsAsHostObjects(bool mode);
  
    /**
     * Write raw data in various common formats to the buffer.
     * Note that integer types are written in base-128 varint format, not with a
     * binary copy. For use during an override of Delegate::WriteHostObject.
     */
    void WriteUint32(uint32_t value);
    void WriteUint64(uint64_t value);
    void WriteDouble(double value);
    void WriteRawBytes(const void* source, size_t length);
  
    ValueSerializer(const ValueSerializer&) = delete;
    void operator=(const ValueSerializer&) = delete;
  
   private:
    struct PrivateData;
    PrivateData* private_;
  };
  
  /**
   * Deserializes values from data written with ValueSerializer, or a compatible
   * implementation.
   */
  class V8_EXPORT ValueDeserializer {
   public:
    class V8_EXPORT Delegate {
     public:
      virtual ~Delegate() = default;
  
      /**
       * The embedder overrides this method to read some kind of host object, if
       * possible. If not, a suitable exception should be thrown and
       * MaybeLocal<Object>() returned.
       */
      virtual MaybeLocal<Object> ReadHostObject(Isolate* isolate);
  
      /**
       * Get a WasmModuleObject given a transfer_id previously provided
       * by ValueSerializer::GetWasmModuleTransferId
       */
      virtual MaybeLocal<WasmModuleObject> GetWasmModuleFromId(
          Isolate* isolate, uint32_t transfer_id);
  
      /**
       * Get a SharedArrayBuffer given a clone_id previously provided
       * by ValueSerializer::GetSharedArrayBufferId
       */
      virtual MaybeLocal<SharedArrayBuffer> GetSharedArrayBufferFromId(
          Isolate* isolate, uint32_t clone_id);
    };
  
    ValueDeserializer(Isolate* isolate, const uint8_t* data, size_t size);
    ValueDeserializer(Isolate* isolate, const uint8_t* data, size_t size,
                      Delegate* delegate);
    ~ValueDeserializer();
  
    /**
     * Reads and validates a header (including the format version).
     * May, for example, reject an invalid or unsupported wire format.
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> ReadHeader(Local<Context> context);
  
    /**
     * Deserializes a JavaScript value from the buffer.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> ReadValue(Local<Context> context);
  
    /**
     * Accepts the array buffer corresponding to the one passed previously to
     * ValueSerializer::TransferArrayBuffer.
     */
    void TransferArrayBuffer(uint32_t transfer_id,
                             Local<ArrayBuffer> array_buffer);
  
    /**
     * Similar to TransferArrayBuffer, but for SharedArrayBuffer.
     * The id is not necessarily in the same namespace as unshared ArrayBuffer
     * objects.
     */
    void TransferSharedArrayBuffer(uint32_t id,
                                   Local<SharedArrayBuffer> shared_array_buffer);
  
    /**
     * Must be called before ReadHeader to enable support for reading the legacy
     * wire format (i.e., which predates this being shipped).
     *
     * Don't use this unless you need to read data written by previous versions of
     * blink::ScriptValueSerializer.
     */
    void SetSupportsLegacyWireFormat(bool supports_legacy_wire_format);
  
    /**
     * Expect inline wasm in the data stream (rather than in-memory transfer)
     */
    void SetExpectInlineWasm(bool allow_inline_wasm);
  
    /**
     * Reads the underlying wire format version. Likely mostly to be useful to
     * legacy code reading old wire format versions. Must be called after
     * ReadHeader.
     */
    uint32_t GetWireFormatVersion() const;
  
    /**
     * Reads raw data in various common formats to the buffer.
     * Note that integer types are read in base-128 varint format, not with a
     * binary copy. For use during an override of Delegate::ReadHostObject.
     */
    V8_WARN_UNUSED_RESULT bool ReadUint32(uint32_t* value);
    V8_WARN_UNUSED_RESULT bool ReadUint64(uint64_t* value);
    V8_WARN_UNUSED_RESULT bool ReadDouble(double* value);
    V8_WARN_UNUSED_RESULT bool ReadRawBytes(size_t length, const void** data);
  
    ValueDeserializer(const ValueDeserializer&) = delete;
    void operator=(const ValueDeserializer&) = delete;
  
   private:
    struct PrivateData;
    PrivateData* private_;
  };
  
  
  // --- Value ---
  
  
  /**
   * The superclass of all JavaScript values and objects.
   */
  class V8_EXPORT Value : public Data {
   public:
    /**
     * Returns true if this value is the undefined value.  See ECMA-262
     * 4.3.10.
     */
    V8_INLINE bool IsUndefined() const;
  
    /**
     * Returns true if this value is the null value.  See ECMA-262
     * 4.3.11.
     */
    V8_INLINE bool IsNull() const;
  
    /**
     * Returns true if this value is either the null or the undefined value.
     * See ECMA-262
     * 4.3.11. and 4.3.12
     */
    V8_INLINE bool IsNullOrUndefined() const;
  
    /**
    * Returns true if this value is true.
    */
    bool IsTrue() const;
  
    /**
     * Returns true if this value is false.
     */
    bool IsFalse() const;
  
    /**
     * Returns true if this value is a symbol or a string.
     */
    bool IsName() const;
  
    /**
     * Returns true if this value is an instance of the String type.
     * See ECMA-262 8.4.
     */
    V8_INLINE bool IsString() const;
  
    /**
     * Returns true if this value is a symbol.
     */
    bool IsSymbol() const;
  
    /**
     * Returns true if this value is a function.
     */
    bool IsFunction() const;
  
    /**
     * Returns true if this value is an array. Note that it will return false for
     * an Proxy for an array.
     */
    bool IsArray() const;
  
    /**
     * Returns true if this value is an object.
     */
    bool IsObject() const;
  
    /**
     * Returns true if this value is a bigint.
     */
    bool IsBigInt() const;
  
    /**
     * Returns true if this value is boolean.
     */
    bool IsBoolean() const;
  
    /**
     * Returns true if this value is a number.
     */
    bool IsNumber() const;
  
    /**
     * Returns true if this value is external.
     */
    bool IsExternal() const;
  
    /**
     * Returns true if this value is a 32-bit signed integer.
     */
    bool IsInt32() const;
  
    /**
     * Returns true if this value is a 32-bit unsigned integer.
     */
    bool IsUint32() const;
  
    /**
     * Returns true if this value is a Date.
     */
    bool IsDate() const;
  
    /**
     * Returns true if this value is an Arguments object.
     */
    bool IsArgumentsObject() const;
  
    /**
     * Returns true if this value is a BigInt object.
     */
    bool IsBigIntObject() const;
  
    /**
     * Returns true if this value is a Boolean object.
     */
    bool IsBooleanObject() const;
  
    /**
     * Returns true if this value is a Number object.
     */
    bool IsNumberObject() const;
  
    /**
     * Returns true if this value is a String object.
     */
    bool IsStringObject() const;
  
    /**
     * Returns true if this value is a Symbol object.
     */
    bool IsSymbolObject() const;
  
    /**
     * Returns true if this value is a NativeError.
     */
    bool IsNativeError() const;
  
    /**
     * Returns true if this value is a RegExp.
     */
    bool IsRegExp() const;
  
    /**
     * Returns true if this value is an async function.
     */
    bool IsAsyncFunction() const;
  
    /**
     * Returns true if this value is a Generator function.
     */
    bool IsGeneratorFunction() const;
  
    /**
     * Returns true if this value is a Generator object (iterator).
     */
    bool IsGeneratorObject() const;
  
    /**
     * Returns true if this value is a Promise.
     */
    bool IsPromise() const;
  
    /**
     * Returns true if this value is a Map.
     */
    bool IsMap() const;
  
    /**
     * Returns true if this value is a Set.
     */
    bool IsSet() const;
  
    /**
     * Returns true if this value is a Map Iterator.
     */
    bool IsMapIterator() const;
  
    /**
     * Returns true if this value is a Set Iterator.
     */
    bool IsSetIterator() const;
  
    /**
     * Returns true if this value is a WeakMap.
     */
    bool IsWeakMap() const;
  
    /**
     * Returns true if this value is a WeakSet.
     */
    bool IsWeakSet() const;
  
    /**
     * Returns true if this value is an ArrayBuffer.
     */
    bool IsArrayBuffer() const;
  
    /**
     * Returns true if this value is an ArrayBufferView.
     */
    bool IsArrayBufferView() const;
  
    /**
     * Returns true if this value is one of TypedArrays.
     */
    bool IsTypedArray() const;
  
    /**
     * Returns true if this value is an Uint8Array.
     */
    bool IsUint8Array() const;
  
    /**
     * Returns true if this value is an Uint8ClampedArray.
     */
    bool IsUint8ClampedArray() const;
  
    /**
     * Returns true if this value is an Int8Array.
     */
    bool IsInt8Array() const;
  
    /**
     * Returns true if this value is an Uint16Array.
     */
    bool IsUint16Array() const;
  
    /**
     * Returns true if this value is an Int16Array.
     */
    bool IsInt16Array() const;
  
    /**
     * Returns true if this value is an Uint32Array.
     */
    bool IsUint32Array() const;
  
    /**
     * Returns true if this value is an Int32Array.
     */
    bool IsInt32Array() const;
  
    /**
     * Returns true if this value is a Float32Array.
     */
    bool IsFloat32Array() const;
  
    /**
     * Returns true if this value is a Float64Array.
     */
    bool IsFloat64Array() const;
  
    /**
     * Returns true if this value is a BigInt64Array.
     */
    bool IsBigInt64Array() const;
  
    /**
     * Returns true if this value is a BigUint64Array.
     */
    bool IsBigUint64Array() const;
  
    /**
     * Returns true if this value is a DataView.
     */
    bool IsDataView() const;
  
    /**
     * Returns true if this value is a SharedArrayBuffer.
     * This is an experimental feature.
     */
    bool IsSharedArrayBuffer() const;
  
    /**
     * Returns true if this value is a JavaScript Proxy.
     */
    bool IsProxy() const;
  
    bool IsWebAssemblyCompiledModule() const;
  
    /**
     * Returns true if the value is a Module Namespace Object.
     */
    bool IsModuleNamespaceObject() const;
  
    V8_WARN_UNUSED_RESULT MaybeLocal<BigInt> ToBigInt(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT MaybeLocal<Number> ToNumber(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT MaybeLocal<String> ToString(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT MaybeLocal<String> ToDetailString(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT MaybeLocal<Object> ToObject(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT MaybeLocal<Integer> ToInteger(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT MaybeLocal<Uint32> ToUint32(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT MaybeLocal<Int32> ToInt32(Local<Context> context) const;
  
    Local<Boolean> ToBoolean(Isolate* isolate) const;
  
    /**
     * Attempts to convert a string to an array index.
     * Returns an empty handle if the conversion fails.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Uint32> ToArrayIndex(
        Local<Context> context) const;
  
    bool BooleanValue(Isolate* isolate) const;
  
    V8_WARN_UNUSED_RESULT Maybe<double> NumberValue(Local<Context> context) const;
    V8_WARN_UNUSED_RESULT Maybe<int64_t> IntegerValue(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT Maybe<uint32_t> Uint32Value(
        Local<Context> context) const;
    V8_WARN_UNUSED_RESULT Maybe<int32_t> Int32Value(Local<Context> context) const;
  
    /** JS == */
    V8_WARN_UNUSED_RESULT Maybe<bool> Equals(Local<Context> context,
                                             Local<Value> that) const;
    bool StrictEquals(Local<Value> that) const;
    bool SameValue(Local<Value> that) const;
  
    template <class T> V8_INLINE static Value* Cast(T* value);
  
    Local<String> TypeOf(Isolate*);
  
    Maybe<bool> InstanceOf(Local<Context> context, Local<Object> object);
  
   private:
    V8_INLINE bool QuickIsUndefined() const;
    V8_INLINE bool QuickIsNull() const;
    V8_INLINE bool QuickIsNullOrUndefined() const;
    V8_INLINE bool QuickIsString() const;
    bool FullIsUndefined() const;
    bool FullIsNull() const;
    bool FullIsString() const;
  };
  
  
  /**
   * The superclass of primitive values.  See ECMA-262 4.3.2.
   */
  class V8_EXPORT Primitive : public Value { };
  
  
  /**
   * A primitive boolean value (ECMA-262, 4.3.14).  Either the true
   * or false value.
   */
  class V8_EXPORT Boolean : public Primitive {
   public:
    bool Value() const;
    V8_INLINE static Boolean* Cast(v8::Value* obj);
    V8_INLINE static Local<Boolean> New(Isolate* isolate, bool value);
  
   private:
    static void CheckCast(v8::Value* obj);
  };
  
  
  /**
   * A superclass for symbols and strings.
   */
  class V8_EXPORT Name : public Primitive {
   public:
    /**
     * Returns the identity hash for this object. The current implementation
     * uses an inline property on the object to store the identity hash.
     *
     * The return value will never be 0. Also, it is not guaranteed to be
     * unique.
     */
    int GetIdentityHash();
  
    V8_INLINE static Name* Cast(Value* obj);
  
   private:
    static void CheckCast(Value* obj);
  };
  
  /**
   * A flag describing different modes of string creation.
   *
   * Aside from performance implications there are no differences between the two
   * creation modes.
   */
  enum class NewStringType {
    /**
     * Create a new string, always allocating new storage memory.
     */
    kNormal,
  
    /**
     * Acts as a hint that the string should be created in the
     * old generation heap space and be deduplicated if an identical string
     * already exists.
     */
    kInternalized
  };
  
  /**
   * A JavaScript string value (ECMA-262, 4.3.17).
   */
  class V8_EXPORT String : public Name {
   public:
    static constexpr int kMaxLength = internal::kApiTaggedSize == 4
                                          ? (1 << 28) - 16
                                          : internal::kSmiMaxValue / 2 - 24;
  
    enum Encoding {
      UNKNOWN_ENCODING = 0x1,
      TWO_BYTE_ENCODING = 0x0,
      ONE_BYTE_ENCODING = 0x8
    };
    /**
     * Returns the number of characters (UTF-16 code units) in this string.
     */
    int Length() const;
  
    /**
     * Returns the number of bytes in the UTF-8 encoded
     * representation of this string.
     */
    int Utf8Length(Isolate* isolate) const;
  
    /**
     * Returns whether this string is known to contain only one byte data,
     * i.e. ISO-8859-1 code points.
     * Does not read the string.
     * False negatives are possible.
     */
    bool IsOneByte() const;
  
    /**
     * Returns whether this string contain only one byte data,
     * i.e. ISO-8859-1 code points.
     * Will read the entire string in some cases.
     */
    bool ContainsOnlyOneByte() const;
  
    /**
     * Write the contents of the string to an external buffer.
     * If no arguments are given, expects the buffer to be large
     * enough to hold the entire string and NULL terminator. Copies
     * the contents of the string and the NULL terminator into the
     * buffer.
     *
     * WriteUtf8 will not write partial UTF-8 sequences, preferring to stop
     * before the end of the buffer.
     *
     * Copies up to length characters into the output buffer.
     * Only null-terminates if there is enough space in the buffer.
     *
     * \param buffer The buffer into which the string will be copied.
     * \param start The starting position within the string at which
     * copying begins.
     * \param length The number of characters to copy from the string.  For
     *    WriteUtf8 the number of bytes in the buffer.
     * \param nchars_ref The number of characters written, can be NULL.
     * \param options Various options that might affect performance of this or
     *    subsequent operations.
     * \return The number of characters copied to the buffer excluding the null
     *    terminator.  For WriteUtf8: The number of bytes copied to the buffer
     *    including the null terminator (if written).
     */
    enum WriteOptions {
      NO_OPTIONS = 0,
      HINT_MANY_WRITES_EXPECTED = 1,
      NO_NULL_TERMINATION = 2,
      PRESERVE_ONE_BYTE_NULL = 4,
      // Used by WriteUtf8 to replace orphan surrogate code units with the
      // unicode replacement character. Needs to be set to guarantee valid UTF-8
      // output.
      REPLACE_INVALID_UTF8 = 8
    };
  
    // 16-bit character codes.
    int Write(Isolate* isolate, uint16_t* buffer, int start = 0, int length = -1,
              int options = NO_OPTIONS) const;
    // One byte characters.
    int WriteOneByte(Isolate* isolate, uint8_t* buffer, int start = 0,
                     int length = -1, int options = NO_OPTIONS) const;
    // UTF-8 encoded characters.
    int WriteUtf8(Isolate* isolate, char* buffer, int length = -1,
                  int* nchars_ref = nullptr, int options = NO_OPTIONS) const;
  
    /**
     * A zero length string.
     */
    V8_INLINE static Local<String> Empty(Isolate* isolate);
  
    /**
     * Returns true if the string is external
     */
    bool IsExternal() const;
  
    /**
     * Returns true if the string is both external and one-byte.
     */
    bool IsExternalOneByte() const;
  
    class V8_EXPORT ExternalStringResourceBase {  // NOLINT
     public:
      virtual ~ExternalStringResourceBase() = default;
  
      /**
       * If a string is cacheable, the value returned by
       * ExternalStringResource::data() may be cached, otherwise it is not
       * expected to be stable beyond the current top-level task.
       */
      virtual bool IsCacheable() const { return true; }
  
      // Disallow copying and assigning.
      ExternalStringResourceBase(const ExternalStringResourceBase&) = delete;
      void operator=(const ExternalStringResourceBase&) = delete;
  
     protected:
      ExternalStringResourceBase() = default;
  
      /**
       * Internally V8 will call this Dispose method when the external string
       * resource is no longer needed. The default implementation will use the
       * delete operator. This method can be overridden in subclasses to
       * control how allocated external string resources are disposed.
       */
      virtual void Dispose() { delete this; }
  
      /**
       * For a non-cacheable string, the value returned by
       * |ExternalStringResource::data()| has to be stable between |Lock()| and
       * |Unlock()|, that is the string must behave as is |IsCacheable()| returned
       * true.
       *
       * These two functions must be thread-safe, and can be called from anywhere.
       * They also must handle lock depth, in the sense that each can be called
       * several times, from different threads, and unlocking should only happen
       * when the balance of Lock() and Unlock() calls is 0.
       */
      virtual void Lock() const {}
  
      /**
       * Unlocks the string.
       */
      virtual void Unlock() const {}
  
     private:
      friend class internal::ExternalString;
      friend class v8::String;
      friend class internal::ScopedExternalStringLock;
    };
  
    /**
     * An ExternalStringResource is a wrapper around a two-byte string
     * buffer that resides outside V8's heap. Implement an
     * ExternalStringResource to manage the life cycle of the underlying
     * buffer.  Note that the string data must be immutable.
     */
    class V8_EXPORT ExternalStringResource
        : public ExternalStringResourceBase {
     public:
      /**
       * Override the destructor to manage the life cycle of the underlying
       * buffer.
       */
      ~ExternalStringResource() override = default;
  
      /**
       * The string data from the underlying buffer.
       */
      virtual const uint16_t* data() const = 0;
  
      /**
       * The length of the string. That is, the number of two-byte characters.
       */
      virtual size_t length() const = 0;
  
     protected:
      ExternalStringResource() = default;
    };
  
    /**
     * An ExternalOneByteStringResource is a wrapper around an one-byte
     * string buffer that resides outside V8's heap. Implement an
     * ExternalOneByteStringResource to manage the life cycle of the
     * underlying buffer.  Note that the string data must be immutable
     * and that the data must be Latin-1 and not UTF-8, which would require
     * special treatment internally in the engine and do not allow efficient
     * indexing.  Use String::New or convert to 16 bit data for non-Latin1.
     */
  
    class V8_EXPORT ExternalOneByteStringResource
        : public ExternalStringResourceBase {
     public:
      /**
       * Override the destructor to manage the life cycle of the underlying
       * buffer.
       */
      ~ExternalOneByteStringResource() override = default;
      /** The string data from the underlying buffer.*/
      virtual const char* data() const = 0;
      /** The number of Latin-1 characters in the string.*/
      virtual size_t length() const = 0;
     protected:
      ExternalOneByteStringResource() = default;
    };
  
    /**
     * If the string is an external string, return the ExternalStringResourceBase
     * regardless of the encoding, otherwise return NULL.  The encoding of the
     * string is returned in encoding_out.
     */
    V8_INLINE ExternalStringResourceBase* GetExternalStringResourceBase(
        Encoding* encoding_out) const;
  
    /**
     * Get the ExternalStringResource for an external string.  Returns
     * NULL if IsExternal() doesn't return true.
     */
    V8_INLINE ExternalStringResource* GetExternalStringResource() const;
  
    /**
     * Get the ExternalOneByteStringResource for an external one-byte string.
     * Returns NULL if IsExternalOneByte() doesn't return true.
     */
    const ExternalOneByteStringResource* GetExternalOneByteStringResource() const;
  
    V8_INLINE static String* Cast(v8::Value* obj);
  
    /** Allocates a new string from UTF-8 data. Only returns an empty value when
     * length > kMaxLength. **/
    static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewFromUtf8(
        Isolate* isolate, const char* data,
        NewStringType type = NewStringType::kNormal, int length = -1);
  
    /** Allocates a new string from Latin-1 data.  Only returns an empty value
     * when length > kMaxLength. **/
    static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewFromOneByte(
        Isolate* isolate, const uint8_t* data,
        NewStringType type = NewStringType::kNormal, int length = -1);
  
    /** Allocates a new string from UTF-16 data. Only returns an empty value when
     * length > kMaxLength. **/
    static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewFromTwoByte(
        Isolate* isolate, const uint16_t* data,
        NewStringType type = NewStringType::kNormal, int length = -1);
  
    /**
     * Creates a new string by concatenating the left and the right strings
     * passed in as parameters.
     */
    static Local<String> Concat(Isolate* isolate, Local<String> left,
                                Local<String> right);
  
    /**
     * Creates a new external string using the data defined in the given
     * resource. When the external string is no longer live on V8's heap the
     * resource will be disposed by calling its Dispose method. The caller of
     * this function should not otherwise delete or modify the resource. Neither
     * should the underlying buffer be deallocated or modified except through the
     * destructor of the external string resource.
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewExternalTwoByte(
        Isolate* isolate, ExternalStringResource* resource);
  
    /**
     * Associate an external string resource with this string by transforming it
     * in place so that existing references to this string in the JavaScript heap
     * will use the external string resource. The external string resource's
     * character contents need to be equivalent to this string.
     * Returns true if the string has been changed to be an external string.
     * The string is not modified if the operation fails. See NewExternal for
     * information on the lifetime of the resource.
     */
    bool MakeExternal(ExternalStringResource* resource);
  
    /**
     * Creates a new external string using the one-byte data defined in the given
     * resource. When the external string is no longer live on V8's heap the
     * resource will be disposed by calling its Dispose method. The caller of
     * this function should not otherwise delete or modify the resource. Neither
     * should the underlying buffer be deallocated or modified except through the
     * destructor of the external string resource.
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewExternalOneByte(
        Isolate* isolate, ExternalOneByteStringResource* resource);
  
    /**
     * Associate an external string resource with this string by transforming it
     * in place so that existing references to this string in the JavaScript heap
     * will use the external string resource. The external string resource's
     * character contents need to be equivalent to this string.
     * Returns true if the string has been changed to be an external string.
     * The string is not modified if the operation fails. See NewExternal for
     * information on the lifetime of the resource.
     */
    bool MakeExternal(ExternalOneByteStringResource* resource);
  
    /**
     * Returns true if this string can be made external.
     */
    bool CanMakeExternal();
  
    /**
     * Returns true if the strings values are equal. Same as JS ==/===.
     */
    bool StringEquals(Local<String> str);
  
    /**
     * Converts an object to a UTF-8-encoded character array.  Useful if
     * you want to print the object.  If conversion to a string fails
     * (e.g. due to an exception in the toString() method of the object)
     * then the length() method returns 0 and the * operator returns
     * NULL.
     */
    class V8_EXPORT Utf8Value {
     public:
      Utf8Value(Isolate* isolate, Local<v8::Value> obj);
      ~Utf8Value();
      char* operator*() { return str_; }
      const char* operator*() const { return str_; }
      int length() const { return length_; }
  
      // Disallow copying and assigning.
      Utf8Value(const Utf8Value&) = delete;
      void operator=(const Utf8Value&) = delete;
  
     private:
      char* str_;
      int length_;
    };
  
    /**
     * Converts an object to a two-byte (UTF-16-encoded) string.
     * If conversion to a string fails (eg. due to an exception in the toString()
     * method of the object) then the length() method returns 0 and the * operator
     * returns NULL.
     */
    class V8_EXPORT Value {
     public:
      Value(Isolate* isolate, Local<v8::Value> obj);
      ~Value();
      uint16_t* operator*() { return str_; }
      const uint16_t* operator*() const { return str_; }
      int length() const { return length_; }
  
      // Disallow copying and assigning.
      Value(const Value&) = delete;
      void operator=(const Value&) = delete;
  
     private:
      uint16_t* str_;
      int length_;
    };
  
   private:
    void VerifyExternalStringResourceBase(ExternalStringResourceBase* v,
                                          Encoding encoding) const;
    void VerifyExternalStringResource(ExternalStringResource* val) const;
    ExternalStringResource* GetExternalStringResourceSlow() const;
    ExternalStringResourceBase* GetExternalStringResourceBaseSlow(
        String::Encoding* encoding_out) const;
  
    static void CheckCast(v8::Value* obj);
  };
  
  
  /**
   * A JavaScript symbol (ECMA-262 edition 6)
   */
  class V8_EXPORT Symbol : public Name {
   public:
    /**
     * Returns the print name string of the symbol, or undefined if none.
     */
    Local<Value> Name() const;
  
    /**
     * Create a symbol. If name is not empty, it will be used as the description.
     */
    static Local<Symbol> New(Isolate* isolate,
                             Local<String> name = Local<String>());
  
    /**
     * Access global symbol registry.
     * Note that symbols created this way are never collected, so
     * they should only be used for statically fixed properties.
     * Also, there is only one global name space for the names used as keys.
     * To minimize the potential for clashes, use qualified names as keys.
     */
    static Local<Symbol> For(Isolate *isolate, Local<String> name);
  
    /**
     * Retrieve a global symbol. Similar to |For|, but using a separate
     * registry that is not accessible by (and cannot clash with) JavaScript code.
     */
    static Local<Symbol> ForApi(Isolate *isolate, Local<String> name);
  
    // Well-known symbols
    static Local<Symbol> GetAsyncIterator(Isolate* isolate);
    static Local<Symbol> GetHasInstance(Isolate* isolate);
    static Local<Symbol> GetIsConcatSpreadable(Isolate* isolate);
    static Local<Symbol> GetIterator(Isolate* isolate);
    static Local<Symbol> GetMatch(Isolate* isolate);
    static Local<Symbol> GetReplace(Isolate* isolate);
    static Local<Symbol> GetSearch(Isolate* isolate);
    static Local<Symbol> GetSplit(Isolate* isolate);
    static Local<Symbol> GetToPrimitive(Isolate* isolate);
    static Local<Symbol> GetToStringTag(Isolate* isolate);
    static Local<Symbol> GetUnscopables(Isolate* isolate);
  
    V8_INLINE static Symbol* Cast(Value* obj);
  
   private:
    Symbol();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * A private symbol
   *
   * This is an experimental feature. Use at your own risk.
   */
  class V8_EXPORT Private : public Data {
   public:
    /**
     * Returns the print name string of the private symbol, or undefined if none.
     */
    Local<Value> Name() const;
  
    /**
     * Create a private symbol. If name is not empty, it will be the description.
     */
    static Local<Private> New(Isolate* isolate,
                              Local<String> name = Local<String>());
  
    /**
     * Retrieve a global private symbol. If a symbol with this name has not
     * been retrieved in the same isolate before, it is created.
     * Note that private symbols created this way are never collected, so
     * they should only be used for statically fixed properties.
     * Also, there is only one global name space for the names used as keys.
     * To minimize the potential for clashes, use qualified names as keys,
     * e.g., "Class#property".
     */
    static Local<Private> ForApi(Isolate* isolate, Local<String> name);
  
    V8_INLINE static Private* Cast(Data* data);
  
   private:
    Private();
  
    static void CheckCast(Data* that);
  };
  
  
  /**
   * A JavaScript number value (ECMA-262, 4.3.20)
   */
  class V8_EXPORT Number : public Primitive {
   public:
    double Value() const;
    static Local<Number> New(Isolate* isolate, double value);
    V8_INLINE static Number* Cast(v8::Value* obj);
   private:
    Number();
    static void CheckCast(v8::Value* obj);
  };
  
  
  /**
   * A JavaScript value representing a signed integer.
   */
  class V8_EXPORT Integer : public Number {
   public:
    static Local<Integer> New(Isolate* isolate, int32_t value);
    static Local<Integer> NewFromUnsigned(Isolate* isolate, uint32_t value);
    int64_t Value() const;
    V8_INLINE static Integer* Cast(v8::Value* obj);
   private:
    Integer();
    static void CheckCast(v8::Value* obj);
  };
  
  
  /**
   * A JavaScript value representing a 32-bit signed integer.
   */
  class V8_EXPORT Int32 : public Integer {
   public:
    int32_t Value() const;
    V8_INLINE static Int32* Cast(v8::Value* obj);
  
   private:
    Int32();
    static void CheckCast(v8::Value* obj);
  };
  
  
  /**
   * A JavaScript value representing a 32-bit unsigned integer.
   */
  class V8_EXPORT Uint32 : public Integer {
   public:
    uint32_t Value() const;
    V8_INLINE static Uint32* Cast(v8::Value* obj);
  
   private:
    Uint32();
    static void CheckCast(v8::Value* obj);
  };
  
  /**
   * A JavaScript BigInt value (https://tc39.github.io/proposal-bigint)
   */
  class V8_EXPORT BigInt : public Primitive {
   public:
    static Local<BigInt> New(Isolate* isolate, int64_t value);
    static Local<BigInt> NewFromUnsigned(Isolate* isolate, uint64_t value);
    /**
     * Creates a new BigInt object using a specified sign bit and a
     * specified list of digits/words.
     * The resulting number is calculated as:
     *
     * (-1)^sign_bit * (words[0] * (2^64)^0 + words[1] * (2^64)^1 + ...)
     */
    static MaybeLocal<BigInt> NewFromWords(Local<Context> context, int sign_bit,
                                           int word_count, const uint64_t* words);
  
    /**
     * Returns the value of this BigInt as an unsigned 64-bit integer.
     * If `lossless` is provided, it will reflect whether the return value was
     * truncated or wrapped around. In particular, it is set to `false` if this
     * BigInt is negative.
     */
    uint64_t Uint64Value(bool* lossless = nullptr) const;
  
    /**
     * Returns the value of this BigInt as a signed 64-bit integer.
     * If `lossless` is provided, it will reflect whether this BigInt was
     * truncated or not.
     */
    int64_t Int64Value(bool* lossless = nullptr) const;
  
    /**
     * Returns the number of 64-bit words needed to store the result of
     * ToWordsArray().
     */
    int WordCount() const;
  
    /**
     * Writes the contents of this BigInt to a specified memory location.
     * `sign_bit` must be provided and will be set to 1 if this BigInt is
     * negative.
     * `*word_count` has to be initialized to the length of the `words` array.
     * Upon return, it will be set to the actual number of words that would
     * be needed to store this BigInt (i.e. the return value of `WordCount()`).
     */
    void ToWordsArray(int* sign_bit, int* word_count, uint64_t* words) const;
  
    V8_INLINE static BigInt* Cast(v8::Value* obj);
  
   private:
    BigInt();
    static void CheckCast(v8::Value* obj);
  };
  
  /**
   * PropertyAttribute.
   */
  enum PropertyAttribute {
    /** None. **/
    None = 0,
    /** ReadOnly, i.e., not writable. **/
    ReadOnly = 1 << 0,
    /** DontEnum, i.e., not enumerable. **/
    DontEnum = 1 << 1,
    /** DontDelete, i.e., not configurable. **/
    DontDelete = 1 << 2
  };
  
  /**
   * Accessor[Getter|Setter] are used as callback functions when
   * setting|getting a particular property. See Object and ObjectTemplate's
   * method SetAccessor.
   */
  typedef void (*AccessorGetterCallback)(
      Local<String> property,
      const PropertyCallbackInfo<Value>& info);
  typedef void (*AccessorNameGetterCallback)(
      Local<Name> property,
      const PropertyCallbackInfo<Value>& info);
  
  
  typedef void (*AccessorSetterCallback)(
      Local<String> property,
      Local<Value> value,
      const PropertyCallbackInfo<void>& info);
  typedef void (*AccessorNameSetterCallback)(
      Local<Name> property,
      Local<Value> value,
      const PropertyCallbackInfo<void>& info);
  
  
  /**
   * Access control specifications.
   *
   * Some accessors should be accessible across contexts.  These
   * accessors have an explicit access control parameter which specifies
   * the kind of cross-context access that should be allowed.
   *
   * TODO(dcarney): Remove PROHIBITS_OVERWRITING as it is now unused.
   */
  enum AccessControl {
    DEFAULT               = 0,
    ALL_CAN_READ          = 1,
    ALL_CAN_WRITE         = 1 << 1,
    PROHIBITS_OVERWRITING = 1 << 2
  };
  
  /**
   * Property filter bits. They can be or'ed to build a composite filter.
   */
  enum PropertyFilter {
    ALL_PROPERTIES = 0,
    ONLY_WRITABLE = 1,
    ONLY_ENUMERABLE = 2,
    ONLY_CONFIGURABLE = 4,
    SKIP_STRINGS = 8,
    SKIP_SYMBOLS = 16
  };
  
  /**
   * Options for marking whether callbacks may trigger JS-observable side effects.
   * Side-effect-free callbacks are whitelisted during debug evaluation with
   * throwOnSideEffect. It applies when calling a Function, FunctionTemplate,
   * or an Accessor callback. For Interceptors, please see
   * PropertyHandlerFlags's kHasNoSideEffect.
   * Callbacks that only cause side effects to the receiver are whitelisted if
   * invoked on receiver objects that are created within the same debug-evaluate
   * call, as these objects are temporary and the side effect does not escape.
   */
  enum class SideEffectType {
    kHasSideEffect,
    kHasNoSideEffect,
    kHasSideEffectToReceiver
  };
  
  /**
   * Keys/Properties filter enums:
   *
   * KeyCollectionMode limits the range of collected properties. kOwnOnly limits
   * the collected properties to the given Object only. kIncludesPrototypes will
   * include all keys of the objects's prototype chain as well.
   */
  enum class KeyCollectionMode { kOwnOnly, kIncludePrototypes };
  
  /**
   * kIncludesIndices allows for integer indices to be collected, while
   * kSkipIndices will exclude integer indices from being collected.
   */
  enum class IndexFilter { kIncludeIndices, kSkipIndices };
  
  /**
   * kConvertToString will convert integer indices to strings.
   * kKeepNumbers will return numbers for integer indices.
   */
  enum class KeyConversionMode { kConvertToString, kKeepNumbers };
  
  /**
   * Integrity level for objects.
   */
  enum class IntegrityLevel { kFrozen, kSealed };
  
  /**
   * A JavaScript object (ECMA-262, 4.3.3)
   */
  class V8_EXPORT Object : public Value {
   public:
    V8_DEPRECATED("Use maybe version",
                  bool Set(Local<Value> key, Local<Value> value));
    /**
     * Set only return Just(true) or Empty(), so if it should never fail, use
     * result.Check().
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> Set(Local<Context> context,
                                          Local<Value> key, Local<Value> value);
  
    V8_DEPRECATED("Use maybe version",
                  bool Set(uint32_t index, Local<Value> value));
    V8_WARN_UNUSED_RESULT Maybe<bool> Set(Local<Context> context, uint32_t index,
                                          Local<Value> value);
  
    // Implements CreateDataProperty (ECMA-262, 7.3.4).
    //
    // Defines a configurable, writable, enumerable property with the given value
    // on the object unless the property already exists and is not configurable
    // or the object is not extensible.
    //
    // Returns true on success.
    V8_WARN_UNUSED_RESULT Maybe<bool> CreateDataProperty(Local<Context> context,
                                                         Local<Name> key,
                                                         Local<Value> value);
    V8_WARN_UNUSED_RESULT Maybe<bool> CreateDataProperty(Local<Context> context,
                                                         uint32_t index,
                                                         Local<Value> value);
  
    // Implements DefineOwnProperty.
    //
    // In general, CreateDataProperty will be faster, however, does not allow
    // for specifying attributes.
    //
    // Returns true on success.
    V8_WARN_UNUSED_RESULT Maybe<bool> DefineOwnProperty(
        Local<Context> context, Local<Name> key, Local<Value> value,
        PropertyAttribute attributes = None);
  
    // Implements Object.DefineProperty(O, P, Attributes), see Ecma-262 19.1.2.4.
    //
    // The defineProperty function is used to add an own property or
    // update the attributes of an existing own property of an object.
    //
    // Both data and accessor descriptors can be used.
    //
    // In general, CreateDataProperty is faster, however, does not allow
    // for specifying attributes or an accessor descriptor.
    //
    // The PropertyDescriptor can change when redefining a property.
    //
    // Returns true on success.
    V8_WARN_UNUSED_RESULT Maybe<bool> DefineProperty(
        Local<Context> context, Local<Name> key, PropertyDescriptor& descriptor);
  
    V8_DEPRECATED("Use maybe version", Local<Value> Get(Local<Value> key));
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> Get(Local<Context> context,
                                                Local<Value> key);
  
    V8_DEPRECATED("Use maybe version", Local<Value> Get(uint32_t index));
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> Get(Local<Context> context,
                                                uint32_t index);
  
    /**
     * Gets the property attributes of a property which can be None or
     * any combination of ReadOnly, DontEnum and DontDelete. Returns
     * None when the property doesn't exist.
     */
    V8_WARN_UNUSED_RESULT Maybe<PropertyAttribute> GetPropertyAttributes(
        Local<Context> context, Local<Value> key);
  
    /**
     * Returns Object.getOwnPropertyDescriptor as per ES2016 section 19.1.2.6.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> GetOwnPropertyDescriptor(
        Local<Context> context, Local<Name> key);
  
    /**
     * Object::Has() calls the abstract operation HasProperty(O, P) described
     * in ECMA-262, 7.3.10. Has() returns
     * true, if the object has the property, either own or on the prototype chain.
     * Interceptors, i.e., PropertyQueryCallbacks, are called if present.
     *
     * Has() has the same side effects as JavaScript's `variable in object`.
     * For example, calling Has() on a revoked proxy will throw an exception.
     *
     * \note Has() converts the key to a name, which possibly calls back into
     * JavaScript.
     *
     * See also v8::Object::HasOwnProperty() and
     * v8::Object::HasRealNamedProperty().
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> Has(Local<Context> context,
                                          Local<Value> key);
  
    V8_WARN_UNUSED_RESULT Maybe<bool> Delete(Local<Context> context,
                                             Local<Value> key);
  
    V8_WARN_UNUSED_RESULT Maybe<bool> Has(Local<Context> context, uint32_t index);
  
    V8_WARN_UNUSED_RESULT Maybe<bool> Delete(Local<Context> context,
                                             uint32_t index);
  
    /**
     * Note: SideEffectType affects the getter only, not the setter.
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> SetAccessor(
        Local<Context> context, Local<Name> name,
        AccessorNameGetterCallback getter,
        AccessorNameSetterCallback setter = nullptr,
        MaybeLocal<Value> data = MaybeLocal<Value>(),
        AccessControl settings = DEFAULT, PropertyAttribute attribute = None,
        SideEffectType getter_side_effect_type = SideEffectType::kHasSideEffect,
        SideEffectType setter_side_effect_type = SideEffectType::kHasSideEffect);
  
    void SetAccessorProperty(Local<Name> name, Local<Function> getter,
                             Local<Function> setter = Local<Function>(),
                             PropertyAttribute attribute = None,
                             AccessControl settings = DEFAULT);
  
    /**
     * Sets a native data property like Template::SetNativeDataProperty, but
     * this method sets on this object directly.
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> SetNativeDataProperty(
        Local<Context> context, Local<Name> name,
        AccessorNameGetterCallback getter,
        AccessorNameSetterCallback setter = nullptr,
        Local<Value> data = Local<Value>(), PropertyAttribute attributes = None,
        SideEffectType getter_side_effect_type = SideEffectType::kHasSideEffect,
        SideEffectType setter_side_effect_type = SideEffectType::kHasSideEffect);
  
    /**
     * Attempts to create a property with the given name which behaves like a data
     * property, except that the provided getter is invoked (and provided with the
     * data value) to supply its value the first time it is read. After the
     * property is accessed once, it is replaced with an ordinary data property.
     *
     * Analogous to Template::SetLazyDataProperty.
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> SetLazyDataProperty(
        Local<Context> context, Local<Name> name,
        AccessorNameGetterCallback getter, Local<Value> data = Local<Value>(),
        PropertyAttribute attributes = None,
        SideEffectType getter_side_effect_type = SideEffectType::kHasSideEffect,
        SideEffectType setter_side_effect_type = SideEffectType::kHasSideEffect);
  
    /**
     * Functionality for private properties.
     * This is an experimental feature, use at your own risk.
     * Note: Private properties are not inherited. Do not rely on this, since it
     * may change.
     */
    Maybe<bool> HasPrivate(Local<Context> context, Local<Private> key);
    Maybe<bool> SetPrivate(Local<Context> context, Local<Private> key,
                           Local<Value> value);
    Maybe<bool> DeletePrivate(Local<Context> context, Local<Private> key);
    MaybeLocal<Value> GetPrivate(Local<Context> context, Local<Private> key);
  
    /**
     * Returns an array containing the names of the enumerable properties
     * of this object, including properties from prototype objects.  The
     * array returned by this method contains the same values as would
     * be enumerated by a for-in statement over this object.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Array> GetPropertyNames(
        Local<Context> context);
    V8_WARN_UNUSED_RESULT MaybeLocal<Array> GetPropertyNames(
        Local<Context> context, KeyCollectionMode mode,
        PropertyFilter property_filter, IndexFilter index_filter,
        KeyConversionMode key_conversion = KeyConversionMode::kKeepNumbers);
  
    /**
     * This function has the same functionality as GetPropertyNames but
     * the returned array doesn't contain the names of properties from
     * prototype objects.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Array> GetOwnPropertyNames(
        Local<Context> context);
  
    /**
     * Returns an array containing the names of the filtered properties
     * of this object, including properties from prototype objects.  The
     * array returned by this method contains the same values as would
     * be enumerated by a for-in statement over this object.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Array> GetOwnPropertyNames(
        Local<Context> context, PropertyFilter filter,
        KeyConversionMode key_conversion = KeyConversionMode::kKeepNumbers);
  
    /**
     * Get the prototype object.  This does not skip objects marked to
     * be skipped by __proto__ and it does not consult the security
     * handler.
     */
    Local<Value> GetPrototype();
  
    /**
     * Set the prototype object.  This does not skip objects marked to
     * be skipped by __proto__ and it does not consult the security
     * handler.
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> SetPrototype(Local<Context> context,
                                                   Local<Value> prototype);
  
    /**
     * Finds an instance of the given function template in the prototype
     * chain.
     */
    Local<Object> FindInstanceInPrototypeChain(Local<FunctionTemplate> tmpl);
  
    /**
     * Call builtin Object.prototype.toString on this object.
     * This is different from Value::ToString() that may call
     * user-defined toString function. This one does not.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<String> ObjectProtoToString(
        Local<Context> context);
  
    /**
     * Returns the name of the function invoked as a constructor for this object.
     */
    Local<String> GetConstructorName();
  
    /**
     * Sets the integrity level of the object.
     */
    Maybe<bool> SetIntegrityLevel(Local<Context> context, IntegrityLevel level);
  
    /** Gets the number of internal fields for this Object. */
    int InternalFieldCount();
  
    /** Same as above, but works for PersistentBase. */
    V8_INLINE static int InternalFieldCount(
        const PersistentBase<Object>& object) {
      return object.val_->InternalFieldCount();
    }
  
    /** Same as above, but works for TracedGlobal. */
    V8_INLINE static int InternalFieldCount(const TracedGlobal<Object>& object) {
      return object.val_->InternalFieldCount();
    }
  
    /** Gets the value from an internal field. */
    V8_INLINE Local<Value> GetInternalField(int index);
  
    /** Sets the value in an internal field. */
    void SetInternalField(int index, Local<Value> value);
  
    /**
     * Gets a 2-byte-aligned native pointer from an internal field. This field
     * must have been set by SetAlignedPointerInInternalField, everything else
     * leads to undefined behavior.
     */
    V8_INLINE void* GetAlignedPointerFromInternalField(int index);
  
    /** Same as above, but works for PersistentBase. */
    V8_INLINE static void* GetAlignedPointerFromInternalField(
        const PersistentBase<Object>& object, int index) {
      return object.val_->GetAlignedPointerFromInternalField(index);
    }
  
    /** Same as above, but works for TracedGlobal. */
    V8_INLINE static void* GetAlignedPointerFromInternalField(
        const TracedGlobal<Object>& object, int index) {
      return object.val_->GetAlignedPointerFromInternalField(index);
    }
  
    /**
     * Sets a 2-byte-aligned native pointer in an internal field. To retrieve such
     * a field, GetAlignedPointerFromInternalField must be used, everything else
     * leads to undefined behavior.
     */
    void SetAlignedPointerInInternalField(int index, void* value);
    void SetAlignedPointerInInternalFields(int argc, int indices[],
                                           void* values[]);
  
    /**
     * HasOwnProperty() is like JavaScript's Object.prototype.hasOwnProperty().
     *
     * See also v8::Object::Has() and v8::Object::HasRealNamedProperty().
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> HasOwnProperty(Local<Context> context,
                                                     Local<Name> key);
    V8_WARN_UNUSED_RESULT Maybe<bool> HasOwnProperty(Local<Context> context,
                                                     uint32_t index);
    /**
     * Use HasRealNamedProperty() if you want to check if an object has an own
     * property without causing side effects, i.e., without calling interceptors.
     *
     * This function is similar to v8::Object::HasOwnProperty(), but it does not
     * call interceptors.
     *
     * \note Consider using non-masking interceptors, i.e., the interceptors are
     * not called if the receiver has the real named property. See
     * `v8::PropertyHandlerFlags::kNonMasking`.
     *
     * See also v8::Object::Has().
     */
    V8_WARN_UNUSED_RESULT Maybe<bool> HasRealNamedProperty(Local<Context> context,
                                                           Local<Name> key);
    V8_WARN_UNUSED_RESULT Maybe<bool> HasRealIndexedProperty(
        Local<Context> context, uint32_t index);
    V8_WARN_UNUSED_RESULT Maybe<bool> HasRealNamedCallbackProperty(
        Local<Context> context, Local<Name> key);
  
    /**
     * If result.IsEmpty() no real property was located in the prototype chain.
     * This means interceptors in the prototype chain are not called.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> GetRealNamedPropertyInPrototypeChain(
        Local<Context> context, Local<Name> key);
  
    /**
     * Gets the property attributes of a real property in the prototype chain,
     * which can be None or any combination of ReadOnly, DontEnum and DontDelete.
     * Interceptors in the prototype chain are not called.
     */
    V8_WARN_UNUSED_RESULT Maybe<PropertyAttribute>
    GetRealNamedPropertyAttributesInPrototypeChain(Local<Context> context,
                                                   Local<Name> key);
  
    /**
     * If result.IsEmpty() no real property was located on the object or
     * in the prototype chain.
     * This means interceptors in the prototype chain are not called.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> GetRealNamedProperty(
        Local<Context> context, Local<Name> key);
  
    /**
     * Gets the property attributes of a real property which can be
     * None or any combination of ReadOnly, DontEnum and DontDelete.
     * Interceptors in the prototype chain are not called.
     */
    V8_WARN_UNUSED_RESULT Maybe<PropertyAttribute> GetRealNamedPropertyAttributes(
        Local<Context> context, Local<Name> key);
  
    /** Tests for a named lookup interceptor.*/
    bool HasNamedLookupInterceptor();
  
    /** Tests for an index lookup interceptor.*/
    bool HasIndexedLookupInterceptor();
  
    /**
     * Returns the identity hash for this object. The current implementation
     * uses a hidden property on the object to store the identity hash.
     *
     * The return value will never be 0. Also, it is not guaranteed to be
     * unique.
     */
    int GetIdentityHash();
  
    /**
     * Clone this object with a fast but shallow copy.  Values will point
     * to the same values as the original object.
     */
    // TODO(dcarney): take an isolate and optionally bail out?
    Local<Object> Clone();
  
    /**
     * Returns the context in which the object was created.
     */
    Local<Context> CreationContext();
  
    /** Same as above, but works for Persistents */
    V8_INLINE static Local<Context> CreationContext(
        const PersistentBase<Object>& object) {
      return object.val_->CreationContext();
    }
  
    /**
     * Checks whether a callback is set by the
     * ObjectTemplate::SetCallAsFunctionHandler method.
     * When an Object is callable this method returns true.
     */
    bool IsCallable();
  
    /**
     * True if this object is a constructor.
     */
    bool IsConstructor();
  
    /**
     * Call an Object as a function if a callback is set by the
     * ObjectTemplate::SetCallAsFunctionHandler method.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> CallAsFunction(Local<Context> context,
                                                           Local<Value> recv,
                                                           int argc,
                                                           Local<Value> argv[]);
  
    /**
     * Call an Object as a constructor if a callback is set by the
     * ObjectTemplate::SetCallAsFunctionHandler method.
     * Note: This method behaves like the Function::NewInstance method.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> CallAsConstructor(
        Local<Context> context, int argc, Local<Value> argv[]);
  
    /**
     * Return the isolate to which the Object belongs to.
     */
    Isolate* GetIsolate();
  
    /**
     * If this object is a Set, Map, WeakSet or WeakMap, this returns a
     * representation of the elements of this object as an array.
     * If this object is a SetIterator or MapIterator, this returns all
     * elements of the underlying collection, starting at the iterator's current
     * position.
     * For other types, this will return an empty MaybeLocal<Array> (without
     * scheduling an exception).
     */
    MaybeLocal<Array> PreviewEntries(bool* is_key_value);
  
    static Local<Object> New(Isolate* isolate);
  
    /**
     * Creates a JavaScript object with the given properties, and
     * a the given prototype_or_null (which can be any JavaScript
     * value, and if it's null, the newly created object won't have
     * a prototype at all). This is similar to Object.create().
     * All properties will be created as enumerable, configurable
     * and writable properties.
     */
    static Local<Object> New(Isolate* isolate, Local<Value> prototype_or_null,
                             Local<Name>* names, Local<Value>* values,
                             size_t length);
  
    V8_INLINE static Object* Cast(Value* obj);
  
   private:
    Object();
    static void CheckCast(Value* obj);
    Local<Value> SlowGetInternalField(int index);
    void* SlowGetAlignedPointerFromInternalField(int index);
  };
  
  
  /**
   * An instance of the built-in array constructor (ECMA-262, 15.4.2).
   */
  class V8_EXPORT Array : public Object {
   public:
    uint32_t Length() const;
  
    /**
     * Creates a JavaScript array with the given length. If the length
     * is negative the returned array will have length 0.
     */
    static Local<Array> New(Isolate* isolate, int length = 0);
  
    /**
     * Creates a JavaScript array out of a Local<Value> array in C++
     * with a known length.
     */
    static Local<Array> New(Isolate* isolate, Local<Value>* elements,
                            size_t length);
    V8_INLINE static Array* Cast(Value* obj);
   private:
    Array();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of the built-in Map constructor (ECMA-262, 6th Edition, 23.1.1).
   */
  class V8_EXPORT Map : public Object {
   public:
    size_t Size() const;
    void Clear();
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> Get(Local<Context> context,
                                                Local<Value> key);
    V8_WARN_UNUSED_RESULT MaybeLocal<Map> Set(Local<Context> context,
                                              Local<Value> key,
                                              Local<Value> value);
    V8_WARN_UNUSED_RESULT Maybe<bool> Has(Local<Context> context,
                                          Local<Value> key);
    V8_WARN_UNUSED_RESULT Maybe<bool> Delete(Local<Context> context,
                                             Local<Value> key);
  
    /**
     * Returns an array of length Size() * 2, where index N is the Nth key and
     * index N + 1 is the Nth value.
     */
    Local<Array> AsArray() const;
  
    /**
     * Creates a new empty Map.
     */
    static Local<Map> New(Isolate* isolate);
  
    V8_INLINE static Map* Cast(Value* obj);
  
   private:
    Map();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of the built-in Set constructor (ECMA-262, 6th Edition, 23.2.1).
   */
  class V8_EXPORT Set : public Object {
   public:
    size_t Size() const;
    void Clear();
    V8_WARN_UNUSED_RESULT MaybeLocal<Set> Add(Local<Context> context,
                                              Local<Value> key);
    V8_WARN_UNUSED_RESULT Maybe<bool> Has(Local<Context> context,
                                          Local<Value> key);
    V8_WARN_UNUSED_RESULT Maybe<bool> Delete(Local<Context> context,
                                             Local<Value> key);
  
    /**
     * Returns an array of the keys in this Set.
     */
    Local<Array> AsArray() const;
  
    /**
     * Creates a new empty Set.
     */
    static Local<Set> New(Isolate* isolate);
  
    V8_INLINE static Set* Cast(Value* obj);
  
   private:
    Set();
    static void CheckCast(Value* obj);
  };
  
  
  template<typename T>
  class ReturnValue {
   public:
    template <class S> V8_INLINE ReturnValue(const ReturnValue<S>& that)
        : value_(that.value_) {
      TYPE_CHECK(T, S);
    }
    // Local setters
    template <typename S>
    V8_INLINE void Set(const Global<S>& handle);
    template <typename S>
    V8_INLINE void Set(const TracedGlobal<S>& handle);
    template <typename S>
    V8_INLINE void Set(const Local<S> handle);
    // Fast primitive setters
    V8_INLINE void Set(bool value);
    V8_INLINE void Set(double i);
    V8_INLINE void Set(int32_t i);
    V8_INLINE void Set(uint32_t i);
    // Fast JS primitive setters
    V8_INLINE void SetNull();
    V8_INLINE void SetUndefined();
    V8_INLINE void SetEmptyString();
    // Convenience getter for Isolate
    V8_INLINE Isolate* GetIsolate() const;
  
    // Pointer setter: Uncompilable to prevent inadvertent misuse.
    template <typename S>
    V8_INLINE void Set(S* whatever);
  
    // Getter. Creates a new Local<> so it comes with a certain performance
    // hit. If the ReturnValue was not yet set, this will return the undefined
    // value.
    V8_INLINE Local<Value> Get() const;
  
   private:
    template<class F> friend class ReturnValue;
    template<class F> friend class FunctionCallbackInfo;
    template<class F> friend class PropertyCallbackInfo;
    template <class F, class G, class H>
    friend class PersistentValueMapBase;
    V8_INLINE void SetInternal(internal::Address value) { *value_ = value; }
    V8_INLINE internal::Address GetDefaultValue();
    V8_INLINE explicit ReturnValue(internal::Address* slot);
    internal::Address* value_;
  };
  
  
  /**
   * The argument information given to function call callbacks.  This
   * class provides access to information about the context of the call,
   * including the receiver, the number and values of arguments, and
   * the holder of the function.
   */
  template<typename T>
  class FunctionCallbackInfo {
   public:
    /** The number of available arguments. */
    V8_INLINE int Length() const;
    /** Accessor for the available arguments. */
    V8_INLINE Local<Value> operator[](int i) const;
    /** Returns the receiver. This corresponds to the "this" value. */
    V8_INLINE Local<Object> This() const;
    /**
     * If the callback was created without a Signature, this is the same
     * value as This(). If there is a signature, and the signature didn't match
     * This() but one of its hidden prototypes, this will be the respective
     * hidden prototype.
     *
     * Note that this is not the prototype of This() on which the accessor
     * referencing this callback was found (which in V8 internally is often
     * referred to as holder [sic]).
     */
    V8_INLINE Local<Object> Holder() const;
    /** For construct calls, this returns the "new.target" value. */
    V8_INLINE Local<Value> NewTarget() const;
    /** Indicates whether this is a regular call or a construct call. */
    V8_INLINE bool IsConstructCall() const;
    /** The data argument specified when creating the callback. */
    V8_INLINE Local<Value> Data() const;
    /** The current Isolate. */
    V8_INLINE Isolate* GetIsolate() const;
    /** The ReturnValue for the call. */
    V8_INLINE ReturnValue<T> GetReturnValue() const;
    // This shouldn't be public, but the arm compiler needs it.
    static const int kArgsLength = 6;
  
   protected:
    friend class internal::FunctionCallbackArguments;
    friend class internal::CustomArguments<FunctionCallbackInfo>;
    friend class debug::ConsoleCallArguments;
    static const int kHolderIndex = 0;
    static const int kIsolateIndex = 1;
    static const int kReturnValueDefaultValueIndex = 2;
    static const int kReturnValueIndex = 3;
    static const int kDataIndex = 4;
    static const int kNewTargetIndex = 5;
  
    V8_INLINE FunctionCallbackInfo(internal::Address* implicit_args,
                                   internal::Address* values, int length);
    internal::Address* implicit_args_;
    internal::Address* values_;
    int length_;
  };
  
  
  /**
   * The information passed to a property callback about the context
   * of the property access.
   */
  template<typename T>
  class PropertyCallbackInfo {
   public:
    /**
     * \return The isolate of the property access.
     */
    V8_INLINE Isolate* GetIsolate() const;
  
    /**
     * \return The data set in the configuration, i.e., in
     * `NamedPropertyHandlerConfiguration` or
     * `IndexedPropertyHandlerConfiguration.`
     */
    V8_INLINE Local<Value> Data() const;
  
    /**
     * \return The receiver. In many cases, this is the object on which the
     * property access was intercepted. When using
     * `Reflect.get`, `Function.prototype.call`, or similar functions, it is the
     * object passed in as receiver or thisArg.
     *
     * \code
     *  void GetterCallback(Local<Name> name,
     *                      const v8::PropertyCallbackInfo<v8::Value>& info) {
     *     auto context = info.GetIsolate()->GetCurrentContext();
     *
     *     v8::Local<v8::Value> a_this =
     *         info.This()
     *             ->GetRealNamedProperty(context, v8_str("a"))
     *             .ToLocalChecked();
     *     v8::Local<v8::Value> a_holder =
     *         info.Holder()
     *             ->GetRealNamedProperty(context, v8_str("a"))
     *             .ToLocalChecked();
     *
     *    CHECK(v8_str("r")->Equals(context, a_this).FromJust());
     *    CHECK(v8_str("obj")->Equals(context, a_holder).FromJust());
     *
     *    info.GetReturnValue().Set(name);
     *  }
     *
     *  v8::Local<v8::FunctionTemplate> templ =
     *  v8::FunctionTemplate::New(isolate);
     *  templ->InstanceTemplate()->SetHandler(
     *      v8::NamedPropertyHandlerConfiguration(GetterCallback));
     *  LocalContext env;
     *  env->Global()
     *      ->Set(env.local(), v8_str("obj"), templ->GetFunction(env.local())
     *                                           .ToLocalChecked()
     *                                           ->NewInstance(env.local())
     *                                           .ToLocalChecked())
     *      .FromJust();
     *
     *  CompileRun("obj.a = 'obj'; var r = {a: 'r'}; Reflect.get(obj, 'x', r)");
     * \endcode
     */
    V8_INLINE Local<Object> This() const;
  
    /**
     * \return The object in the prototype chain of the receiver that has the
     * interceptor. Suppose you have `x` and its prototype is `y`, and `y`
     * has an interceptor. Then `info.This()` is `x` and `info.Holder()` is `y`.
     * The Holder() could be a hidden object (the global object, rather
     * than the global proxy).
     *
     * \note For security reasons, do not pass the object back into the runtime.
     */
    V8_INLINE Local<Object> Holder() const;
  
    /**
     * \return The return value of the callback.
     * Can be changed by calling Set().
     * \code
     * info.GetReturnValue().Set(...)
     * \endcode
     *
     */
    V8_INLINE ReturnValue<T> GetReturnValue() const;
  
    /**
     * \return True if the intercepted function should throw if an error occurs.
     * Usually, `true` corresponds to `'use strict'`.
     *
     * \note Always `false` when intercepting `Reflect.set()`
     * independent of the language mode.
     */
    V8_INLINE bool ShouldThrowOnError() const;
  
    // This shouldn't be public, but the arm compiler needs it.
    static const int kArgsLength = 7;
  
   protected:
    friend class MacroAssembler;
    friend class internal::PropertyCallbackArguments;
    friend class internal::CustomArguments<PropertyCallbackInfo>;
    static const int kShouldThrowOnErrorIndex = 0;
    static const int kHolderIndex = 1;
    static const int kIsolateIndex = 2;
    static const int kReturnValueDefaultValueIndex = 3;
    static const int kReturnValueIndex = 4;
    static const int kDataIndex = 5;
    static const int kThisIndex = 6;
  
    V8_INLINE PropertyCallbackInfo(internal::Address* args) : args_(args) {}
    internal::Address* args_;
  };
  
  
  typedef void (*FunctionCallback)(const FunctionCallbackInfo<Value>& info);
  
  enum class ConstructorBehavior { kThrow, kAllow };
  
  /**
   * A JavaScript function object (ECMA-262, 15.3).
   */
  class V8_EXPORT Function : public Object {
   public:
    /**
     * Create a function in the current execution context
     * for a given FunctionCallback.
     */
    static MaybeLocal<Function> New(
        Local<Context> context, FunctionCallback callback,
        Local<Value> data = Local<Value>(), int length = 0,
        ConstructorBehavior behavior = ConstructorBehavior::kAllow,
        SideEffectType side_effect_type = SideEffectType::kHasSideEffect);
  
    V8_WARN_UNUSED_RESULT MaybeLocal<Object> NewInstance(
        Local<Context> context, int argc, Local<Value> argv[]) const;
  
    V8_WARN_UNUSED_RESULT MaybeLocal<Object> NewInstance(
        Local<Context> context) const {
      return NewInstance(context, 0, nullptr);
    }
  
    /**
     * When side effect checks are enabled, passing kHasNoSideEffect allows the
     * constructor to be invoked without throwing. Calls made within the
     * constructor are still checked.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Object> NewInstanceWithSideEffectType(
        Local<Context> context, int argc, Local<Value> argv[],
        SideEffectType side_effect_type = SideEffectType::kHasSideEffect) const;
  
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> Call(Local<Context> context,
                                                 Local<Value> recv, int argc,
                                                 Local<Value> argv[]);
  
    void SetName(Local<String> name);
    Local<Value> GetName() const;
  
    /**
     * Name inferred from variable or property assignment of this function.
     * Used to facilitate debugging and profiling of JavaScript code written
     * in an OO style, where many functions are anonymous but are assigned
     * to object properties.
     */
    Local<Value> GetInferredName() const;
  
    /**
     * displayName if it is set, otherwise name if it is configured, otherwise
     * function name, otherwise inferred name.
     */
    Local<Value> GetDebugName() const;
  
    /**
     * User-defined name assigned to the "displayName" property of this function.
     * Used to facilitate debugging and profiling of JavaScript code.
     */
    Local<Value> GetDisplayName() const;
  
    /**
     * Returns zero based line number of function body and
     * kLineOffsetNotFound if no information available.
     */
    int GetScriptLineNumber() const;
    /**
     * Returns zero based column number of function body and
     * kLineOffsetNotFound if no information available.
     */
    int GetScriptColumnNumber() const;
  
    /**
     * Returns scriptId.
     */
    int ScriptId() const;
  
    /**
     * Returns the original function if this function is bound, else returns
     * v8::Undefined.
     */
    Local<Value> GetBoundFunction() const;
  
    ScriptOrigin GetScriptOrigin() const;
    V8_INLINE static Function* Cast(Value* obj);
    static const int kLineOffsetNotFound;
  
   private:
    Function();
    static void CheckCast(Value* obj);
  };
  
  #ifndef V8_PROMISE_INTERNAL_FIELD_COUNT
  // The number of required internal fields can be defined by embedder.
  #define V8_PROMISE_INTERNAL_FIELD_COUNT 0
  #endif
  
  /**
   * An instance of the built-in Promise constructor (ES6 draft).
   */
  class V8_EXPORT Promise : public Object {
   public:
    /**
     * State of the promise. Each value corresponds to one of the possible values
     * of the [[PromiseState]] field.
     */
    enum PromiseState { kPending, kFulfilled, kRejected };
  
    class V8_EXPORT Resolver : public Object {
     public:
      /**
       * Create a new resolver, along with an associated promise in pending state.
       */
      static V8_WARN_UNUSED_RESULT MaybeLocal<Resolver> New(
          Local<Context> context);
  
      /**
       * Extract the associated promise.
       */
      Local<Promise> GetPromise();
  
      /**
       * Resolve/reject the associated promise with a given value.
       * Ignored if the promise is no longer pending.
       */
      V8_WARN_UNUSED_RESULT Maybe<bool> Resolve(Local<Context> context,
                                                Local<Value> value);
  
      V8_WARN_UNUSED_RESULT Maybe<bool> Reject(Local<Context> context,
                                               Local<Value> value);
  
      V8_INLINE static Resolver* Cast(Value* obj);
  
     private:
      Resolver();
      static void CheckCast(Value* obj);
    };
  
    /**
     * Register a resolution/rejection handler with a promise.
     * The handler is given the respective resolution/rejection value as
     * an argument. If the promise is already resolved/rejected, the handler is
     * invoked at the end of turn.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Promise> Catch(Local<Context> context,
                                                    Local<Function> handler);
  
    V8_WARN_UNUSED_RESULT MaybeLocal<Promise> Then(Local<Context> context,
                                                   Local<Function> handler);
  
    V8_WARN_UNUSED_RESULT MaybeLocal<Promise> Then(Local<Context> context,
                                                   Local<Function> on_fulfilled,
                                                   Local<Function> on_rejected);
  
    /**
     * Returns true if the promise has at least one derived promise, and
     * therefore resolve/reject handlers (including default handler).
     */
    bool HasHandler();
  
    /**
     * Returns the content of the [[PromiseResult]] field. The Promise must not
     * be pending.
     */
    Local<Value> Result();
  
    /**
     * Returns the value of the [[PromiseState]] field.
     */
    PromiseState State();
  
    /**
     * Marks this promise as handled to avoid reporting unhandled rejections.
     */
    void MarkAsHandled();
  
    V8_INLINE static Promise* Cast(Value* obj);
  
    static const int kEmbedderFieldCount = V8_PROMISE_INTERNAL_FIELD_COUNT;
  
   private:
    Promise();
    static void CheckCast(Value* obj);
  };
  
  /**
   * An instance of a Property Descriptor, see Ecma-262 6.2.4.
   *
   * Properties in a descriptor are present or absent. If you do not set
   * `enumerable`, `configurable`, and `writable`, they are absent. If `value`,
   * `get`, or `set` are absent, but you must specify them in the constructor, use
   * empty handles.
   *
   * Accessors `get` and `set` must be callable or undefined if they are present.
   *
   * \note Only query properties if they are present, i.e., call `x()` only if
   * `has_x()` returns true.
   *
   * \code
   * // var desc = {writable: false}
   * v8::PropertyDescriptor d(Local<Value>()), false);
   * d.value(); // error, value not set
   * if (d.has_writable()) {
   *   d.writable(); // false
   * }
   *
   * // var desc = {value: undefined}
   * v8::PropertyDescriptor d(v8::Undefined(isolate));
   *
   * // var desc = {get: undefined}
   * v8::PropertyDescriptor d(v8::Undefined(isolate), Local<Value>()));
   * \endcode
   */
  class V8_EXPORT PropertyDescriptor {
   public:
    // GenericDescriptor
    PropertyDescriptor();
  
    // DataDescriptor
    explicit PropertyDescriptor(Local<Value> value);
  
    // DataDescriptor with writable property
    PropertyDescriptor(Local<Value> value, bool writable);
  
    // AccessorDescriptor
    PropertyDescriptor(Local<Value> get, Local<Value> set);
  
    ~PropertyDescriptor();
  
    Local<Value> value() const;
    bool has_value() const;
  
    Local<Value> get() const;
    bool has_get() const;
    Local<Value> set() const;
    bool has_set() const;
  
    void set_enumerable(bool enumerable);
    bool enumerable() const;
    bool has_enumerable() const;
  
    void set_configurable(bool configurable);
    bool configurable() const;
    bool has_configurable() const;
  
    bool writable() const;
    bool has_writable() const;
  
    struct PrivateData;
    PrivateData* get_private() const { return private_; }
  
    PropertyDescriptor(const PropertyDescriptor&) = delete;
    void operator=(const PropertyDescriptor&) = delete;
  
   private:
    PrivateData* private_;
  };
  
  /**
   * An instance of the built-in Proxy constructor (ECMA-262, 6th Edition,
   * 26.2.1).
   */
  class V8_EXPORT Proxy : public Object {
   public:
    Local<Value> GetTarget();
    Local<Value> GetHandler();
    bool IsRevoked();
    void Revoke();
  
    /**
     * Creates a new Proxy for the target object.
     */
    static MaybeLocal<Proxy> New(Local<Context> context,
                                 Local<Object> local_target,
                                 Local<Object> local_handler);
  
    V8_INLINE static Proxy* Cast(Value* obj);
  
   private:
    Proxy();
    static void CheckCast(Value* obj);
  };
  
  /**
   * Points to an unowned continous buffer holding a known number of elements.
   *
   * This is similar to std::span (under consideration for C++20), but does not
   * require advanced C++ support. In the (far) future, this may be replaced with
   * or aliased to std::span.
   *
   * To facilitate future migration, this class exposes a subset of the interface
   * implemented by std::span.
   */
  template <typename T>
  class V8_EXPORT MemorySpan {
   public:
    /** The default constructor creates an empty span. */
    constexpr MemorySpan() = default;
  
    constexpr MemorySpan(T* data, size_t size) : data_(data), size_(size) {}
  
    /** Returns a pointer to the beginning of the buffer. */
    constexpr T* data() const { return data_; }
    /** Returns the number of elements that the buffer holds. */
    constexpr size_t size() const { return size_; }
  
   private:
    T* data_ = nullptr;
    size_t size_ = 0;
  };
  
  /**
   * An owned byte buffer with associated size.
   */
  struct OwnedBuffer {
    std::unique_ptr<const uint8_t[]> buffer;
    size_t size = 0;
    OwnedBuffer(std::unique_ptr<const uint8_t[]> buffer, size_t size)
        : buffer(std::move(buffer)), size(size) {}
    OwnedBuffer() = default;
  };
  
  // Wrapper around a compiled WebAssembly module, which is potentially shared by
  // different WasmModuleObjects.
  class V8_EXPORT CompiledWasmModule {
   public:
    /**
     * Serialize the compiled module. The serialized data does not include the
     * wire bytes.
     */
    OwnedBuffer Serialize();
  
    /**
     * Get the (wasm-encoded) wire bytes that were used to compile this module.
     */
    MemorySpan<const uint8_t> GetWireBytesRef();
  
   private:
    explicit CompiledWasmModule(std::shared_ptr<internal::wasm::NativeModule>);
    friend class Utils;
  
    const std::shared_ptr<internal::wasm::NativeModule> native_module_;
  };
  
  // An instance of WebAssembly.Module.
  class V8_EXPORT WasmModuleObject : public Object {
   public:
    /**
     * An opaque, native heap object for transferring wasm modules. It
     * supports move semantics, and does not support copy semantics.
     * TODO(wasm): Merge this with CompiledWasmModule once code sharing is always
     * enabled.
     */
    class TransferrableModule final {
     public:
      TransferrableModule(TransferrableModule&& src) = default;
      TransferrableModule(const TransferrableModule& src) = delete;
  
      TransferrableModule& operator=(TransferrableModule&& src) = default;
      TransferrableModule& operator=(const TransferrableModule& src) = delete;
  
     private:
      typedef std::shared_ptr<internal::wasm::NativeModule> SharedModule;
      friend class WasmModuleObject;
      explicit TransferrableModule(SharedModule shared_module)
          : shared_module_(std::move(shared_module)) {}
      TransferrableModule(OwnedBuffer serialized, OwnedBuffer bytes)
          : serialized_(std::move(serialized)), wire_bytes_(std::move(bytes)) {}
  
      SharedModule shared_module_;
      OwnedBuffer serialized_ = {nullptr, 0};
      OwnedBuffer wire_bytes_ = {nullptr, 0};
    };
  
    /**
     * Get an in-memory, non-persistable, and context-independent (meaning,
     * suitable for transfer to another Isolate and Context) representation
     * of this wasm compiled module.
     */
    TransferrableModule GetTransferrableModule();
  
    /**
     * Efficiently re-create a WasmModuleObject, without recompiling, from
     * a TransferrableModule.
     */
    static MaybeLocal<WasmModuleObject> FromTransferrableModule(
        Isolate* isolate, const TransferrableModule&);
  
    /**
     * Get the compiled module for this module object. The compiled module can be
     * shared by several module objects.
     */
    CompiledWasmModule GetCompiledModule();
  
    /**
     * If possible, deserialize the module, otherwise compile it from the provided
     * uncompiled bytes.
     */
    static MaybeLocal<WasmModuleObject> DeserializeOrCompile(
        Isolate* isolate, MemorySpan<const uint8_t> serialized_module,
        MemorySpan<const uint8_t> wire_bytes);
    V8_INLINE static WasmModuleObject* Cast(Value* obj);
  
   private:
    static MaybeLocal<WasmModuleObject> Deserialize(
        Isolate* isolate, MemorySpan<const uint8_t> serialized_module,
        MemorySpan<const uint8_t> wire_bytes);
    static MaybeLocal<WasmModuleObject> Compile(Isolate* isolate,
                                                const uint8_t* start,
                                                size_t length);
    static MemorySpan<const uint8_t> AsReference(const OwnedBuffer& buff) {
      return {buff.buffer.get(), buff.size};
    }
  
    WasmModuleObject();
    static void CheckCast(Value* obj);
  };
  
  /**
   * The V8 interface for WebAssembly streaming compilation. When streaming
   * compilation is initiated, V8 passes a {WasmStreaming} object to the embedder
   * such that the embedder can pass the input bytes for streaming compilation to
   * V8.
   */
  class V8_EXPORT WasmStreaming final {
   public:
    class WasmStreamingImpl;
  
    /**
     * Client to receive streaming event notifications.
     */
    class Client {
     public:
      virtual ~Client() = default;
      /**
       * Passes the fully compiled module to the client. This can be used to
       * implement code caching.
       */
      virtual void OnModuleCompiled(CompiledWasmModule compiled_module) = 0;
    };
  
    explicit WasmStreaming(std::unique_ptr<WasmStreamingImpl> impl);
  
    ~WasmStreaming();
  
    /**
     * Pass a new chunk of bytes to WebAssembly streaming compilation.
     * The buffer passed into {OnBytesReceived} is owned by the caller.
     */
    void OnBytesReceived(const uint8_t* bytes, size_t size);
  
    /**
     * {Finish} should be called after all received bytes where passed to
     * {OnBytesReceived} to tell V8 that there will be no more bytes. {Finish}
     * does not have to be called after {Abort} has been called already.
     */
    void Finish();
  
    /**
     * Abort streaming compilation. If {exception} has a value, then the promise
     * associated with streaming compilation is rejected with that value. If
     * {exception} does not have value, the promise does not get rejected.
     */
    void Abort(MaybeLocal<Value> exception);
  
    /**
     * Passes previously compiled module bytes. This must be called before
     * {OnBytesReceived}, {Finish}, or {Abort}. Returns true if the module bytes
     * can be used, false otherwise. The buffer passed via {bytes} and {size}
     * is owned by the caller. If {SetCompiledModuleBytes} returns true, the
     * buffer must remain valid until either {Finish} or {Abort} completes.
     */
    bool SetCompiledModuleBytes(const uint8_t* bytes, size_t size);
  
    /**
     * Sets the client object that will receive streaming event notifications.
     * This must be called before {OnBytesReceived}, {Finish}, or {Abort}.
     */
    void SetClient(std::shared_ptr<Client> client);
  
    /**
     * Unpacks a {WasmStreaming} object wrapped in a  {Managed} for the embedder.
     * Since the embedder is on the other side of the API, it cannot unpack the
     * {Managed} itself.
     */
    static std::shared_ptr<WasmStreaming> Unpack(Isolate* isolate,
                                                 Local<Value> value);
  
   private:
    std::unique_ptr<WasmStreamingImpl> impl_;
  };
  
  // TODO(mtrofin): when streaming compilation is done, we can rename this
  // to simply WasmModuleObjectBuilder
  class V8_EXPORT WasmModuleObjectBuilderStreaming final {
   public:
    explicit WasmModuleObjectBuilderStreaming(Isolate* isolate);
    /**
     * The buffer passed into OnBytesReceived is owned by the caller.
     */
    void OnBytesReceived(const uint8_t*, size_t size);
    void Finish();
    /**
     * Abort streaming compilation. If {exception} has a value, then the promise
     * associated with streaming compilation is rejected with that value. If
     * {exception} does not have value, the promise does not get rejected.
     */
    void Abort(MaybeLocal<Value> exception);
    Local<Promise> GetPromise();
  
    ~WasmModuleObjectBuilderStreaming() = default;
  
   private:
    WasmModuleObjectBuilderStreaming(const WasmModuleObjectBuilderStreaming&) =
        delete;
    WasmModuleObjectBuilderStreaming(WasmModuleObjectBuilderStreaming&&) =
        default;
    WasmModuleObjectBuilderStreaming& operator=(
        const WasmModuleObjectBuilderStreaming&) = delete;
    WasmModuleObjectBuilderStreaming& operator=(
        WasmModuleObjectBuilderStreaming&&) = default;
    Isolate* isolate_ = nullptr;
  
  #if V8_CC_MSVC
    /**
     * We don't need the static Copy API, so the default
     * NonCopyablePersistentTraits would be sufficient, however,
     * MSVC eagerly instantiates the Copy.
     * We ensure we don't use Copy, however, by compiling with the
     * defaults everywhere else.
     */
    Persistent<Promise, CopyablePersistentTraits<Promise>> promise_;
  #else
    Persistent<Promise> promise_;
  #endif
    std::shared_ptr<internal::wasm::StreamingDecoder> streaming_decoder_;
  };
  
  #ifndef V8_ARRAY_BUFFER_INTERNAL_FIELD_COUNT
  // The number of required internal fields can be defined by embedder.
  #define V8_ARRAY_BUFFER_INTERNAL_FIELD_COUNT 2
  #endif
  
  
  enum class ArrayBufferCreationMode { kInternalized, kExternalized };
  
  
  /**
   * An instance of the built-in ArrayBuffer constructor (ES6 draft 15.13.5).
   */
  class V8_EXPORT ArrayBuffer : public Object {
   public:
    /**
     * A thread-safe allocator that V8 uses to allocate |ArrayBuffer|'s memory.
     * The allocator is a global V8 setting. It has to be set via
     * Isolate::CreateParams.
     *
     * Memory allocated through this allocator by V8 is accounted for as external
     * memory by V8. Note that V8 keeps track of the memory for all internalized
     * |ArrayBuffer|s. Responsibility for tracking external memory (using
     * Isolate::AdjustAmountOfExternalAllocatedMemory) is handed over to the
     * embedder upon externalization and taken over upon internalization (creating
     * an internalized buffer from an existing buffer).
     *
     * Note that it is unsafe to call back into V8 from any of the allocator
     * functions.
     */
    class V8_EXPORT Allocator { // NOLINT
     public:
      virtual ~Allocator() = default;
  
      /**
       * Allocate |length| bytes. Return NULL if allocation is not successful.
       * Memory should be initialized to zeroes.
       */
      virtual void* Allocate(size_t length) = 0;
  
      /**
       * Allocate |length| bytes. Return NULL if allocation is not successful.
       * Memory does not have to be initialized.
       */
      virtual void* AllocateUninitialized(size_t length) = 0;
  
      /**
       * Free the memory block of size |length|, pointed to by |data|.
       * That memory is guaranteed to be previously allocated by |Allocate|.
       */
      virtual void Free(void* data, size_t length) = 0;
  
      /**
       * ArrayBuffer allocation mode. kNormal is a malloc/free style allocation,
       * while kReservation is for larger allocations with the ability to set
       * access permissions.
       */
      enum class AllocationMode { kNormal, kReservation };
  
      /**
       * malloc/free based convenience allocator.
       *
       * Caller takes ownership, i.e. the returned object needs to be freed using
       * |delete allocator| once it is no longer in use.
       */
      static Allocator* NewDefaultAllocator();
    };
  
    /**
     * The contents of an |ArrayBuffer|. Externalization of |ArrayBuffer|
     * returns an instance of this class, populated, with a pointer to data
     * and byte length.
     *
     * The Data pointer of ArrayBuffer::Contents must be freed using the provided
     * deleter, which will call ArrayBuffer::Allocator::Free if the buffer
     * was allocated with ArraryBuffer::Allocator::Allocate.
     */
    class V8_EXPORT Contents { // NOLINT
     public:
      using DeleterCallback = void (*)(void* buffer, size_t length, void* info);
  
      Contents()
          : data_(nullptr),
            byte_length_(0),
            allocation_base_(nullptr),
            allocation_length_(0),
            allocation_mode_(Allocator::AllocationMode::kNormal),
            deleter_(nullptr),
            deleter_data_(nullptr) {}
  
      void* AllocationBase() const { return allocation_base_; }
      size_t AllocationLength() const { return allocation_length_; }
      Allocator::AllocationMode AllocationMode() const {
        return allocation_mode_;
      }
  
      void* Data() const { return data_; }
      size_t ByteLength() const { return byte_length_; }
      DeleterCallback Deleter() const { return deleter_; }
      void* DeleterData() const { return deleter_data_; }
  
     private:
      Contents(void* data, size_t byte_length, void* allocation_base,
               size_t allocation_length,
               Allocator::AllocationMode allocation_mode, DeleterCallback deleter,
               void* deleter_data);
  
      void* data_;
      size_t byte_length_;
      void* allocation_base_;
      size_t allocation_length_;
      Allocator::AllocationMode allocation_mode_;
      DeleterCallback deleter_;
      void* deleter_data_;
  
      friend class ArrayBuffer;
    };
  
  
    /**
     * Data length in bytes.
     */
    size_t ByteLength() const;
  
    /**
     * Create a new ArrayBuffer. Allocate |byte_length| bytes.
     * Allocated memory will be owned by a created ArrayBuffer and
     * will be deallocated when it is garbage-collected,
     * unless the object is externalized.
     */
    static Local<ArrayBuffer> New(Isolate* isolate, size_t byte_length);
  
    /**
     * Create a new ArrayBuffer over an existing memory block.
     * The created array buffer is by default immediately in externalized state.
     * In externalized state, the memory block will not be reclaimed when a
     * created ArrayBuffer is garbage-collected.
     * In internalized state, the memory block will be released using
     * |Allocator::Free| once all ArrayBuffers referencing it are collected by
     * the garbage collector.
     */
    static Local<ArrayBuffer> New(
        Isolate* isolate, void* data, size_t byte_length,
        ArrayBufferCreationMode mode = ArrayBufferCreationMode::kExternalized);
  
    /**
     * Returns true if ArrayBuffer is externalized, that is, does not
     * own its memory block.
     */
    bool IsExternal() const;
  
    /**
     * Returns true if this ArrayBuffer may be detached.
     */
    bool IsDetachable() const;
  
    // TODO(913887): fix the use of 'neuter' in the API.
    V8_DEPRECATE_SOON("Use IsDetachable() instead.",
                      inline bool IsNeuterable() const) {
      return IsDetachable();
    }
  
    /**
     * Detaches this ArrayBuffer and all its views (typed arrays).
     * Detaching sets the byte length of the buffer and all typed arrays to zero,
     * preventing JavaScript from ever accessing underlying backing store.
     * ArrayBuffer should have been externalized and must be detachable.
     */
    void Detach();
  
    // TODO(913887): fix the use of 'neuter' in the API.
    V8_DEPRECATE_SOON("Use Detach() instead.", inline void Neuter()) { Detach(); }
  
    /**
     * Make this ArrayBuffer external. The pointer to underlying memory block
     * and byte length are returned as |Contents| structure. After ArrayBuffer
     * had been externalized, it does no longer own the memory block. The caller
     * should take steps to free memory when it is no longer needed.
     *
     * The Data pointer of ArrayBuffer::Contents must be freed using the provided
     * deleter, which will call ArrayBuffer::Allocator::Free if the buffer
     * was allocated with ArraryBuffer::Allocator::Allocate.
     */
    Contents Externalize();
  
    /**
     * Get a pointer to the ArrayBuffer's underlying memory block without
     * externalizing it. If the ArrayBuffer is not externalized, this pointer
     * will become invalid as soon as the ArrayBuffer gets garbage collected.
     *
     * The embedder should make sure to hold a strong reference to the
     * ArrayBuffer while accessing this pointer.
     */
    Contents GetContents();
  
    V8_INLINE static ArrayBuffer* Cast(Value* obj);
  
    static const int kInternalFieldCount = V8_ARRAY_BUFFER_INTERNAL_FIELD_COUNT;
    static const int kEmbedderFieldCount = V8_ARRAY_BUFFER_INTERNAL_FIELD_COUNT;
  
   private:
    ArrayBuffer();
    static void CheckCast(Value* obj);
  };
  
  
  #ifndef V8_ARRAY_BUFFER_VIEW_INTERNAL_FIELD_COUNT
  // The number of required internal fields can be defined by embedder.
  #define V8_ARRAY_BUFFER_VIEW_INTERNAL_FIELD_COUNT 2
  #endif
  
  
  /**
   * A base class for an instance of one of "views" over ArrayBuffer,
   * including TypedArrays and DataView (ES6 draft 15.13).
   */
  class V8_EXPORT ArrayBufferView : public Object {
   public:
    /**
     * Returns underlying ArrayBuffer.
     */
    Local<ArrayBuffer> Buffer();
    /**
     * Byte offset in |Buffer|.
     */
    size_t ByteOffset();
    /**
     * Size of a view in bytes.
     */
    size_t ByteLength();
  
    /**
     * Copy the contents of the ArrayBufferView's buffer to an embedder defined
     * memory without additional overhead that calling ArrayBufferView::Buffer
     * might incur.
     *
     * Will write at most min(|byte_length|, ByteLength) bytes starting at
     * ByteOffset of the underlying buffer to the memory starting at |dest|.
     * Returns the number of bytes actually written.
     */
    size_t CopyContents(void* dest, size_t byte_length);
  
    /**
     * Returns true if ArrayBufferView's backing ArrayBuffer has already been
     * allocated.
     */
    bool HasBuffer() const;
  
    V8_INLINE static ArrayBufferView* Cast(Value* obj);
  
    static const int kInternalFieldCount =
        V8_ARRAY_BUFFER_VIEW_INTERNAL_FIELD_COUNT;
    static const int kEmbedderFieldCount =
        V8_ARRAY_BUFFER_VIEW_INTERNAL_FIELD_COUNT;
  
   private:
    ArrayBufferView();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * A base class for an instance of TypedArray series of constructors
   * (ES6 draft 15.13.6).
   */
  class V8_EXPORT TypedArray : public ArrayBufferView {
   public:
    /*
     * The largest typed array size that can be constructed using New.
     */
    static constexpr size_t kMaxLength = internal::kSmiMaxValue;
  
    /**
     * Number of elements in this typed array
     * (e.g. for Int16Array, |ByteLength|/2).
     */
    size_t Length();
  
    V8_INLINE static TypedArray* Cast(Value* obj);
  
   private:
    TypedArray();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of Uint8Array constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Uint8Array : public TypedArray {
   public:
    static Local<Uint8Array> New(Local<ArrayBuffer> array_buffer,
                                 size_t byte_offset, size_t length);
    static Local<Uint8Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                 size_t byte_offset, size_t length);
    V8_INLINE static Uint8Array* Cast(Value* obj);
  
   private:
    Uint8Array();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of Uint8ClampedArray constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Uint8ClampedArray : public TypedArray {
   public:
    static Local<Uint8ClampedArray> New(Local<ArrayBuffer> array_buffer,
                                        size_t byte_offset, size_t length);
    static Local<Uint8ClampedArray> New(
        Local<SharedArrayBuffer> shared_array_buffer, size_t byte_offset,
        size_t length);
    V8_INLINE static Uint8ClampedArray* Cast(Value* obj);
  
   private:
    Uint8ClampedArray();
    static void CheckCast(Value* obj);
  };
  
  /**
   * An instance of Int8Array constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Int8Array : public TypedArray {
   public:
    static Local<Int8Array> New(Local<ArrayBuffer> array_buffer,
                                size_t byte_offset, size_t length);
    static Local<Int8Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                size_t byte_offset, size_t length);
    V8_INLINE static Int8Array* Cast(Value* obj);
  
   private:
    Int8Array();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of Uint16Array constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Uint16Array : public TypedArray {
   public:
    static Local<Uint16Array> New(Local<ArrayBuffer> array_buffer,
                                  size_t byte_offset, size_t length);
    static Local<Uint16Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                  size_t byte_offset, size_t length);
    V8_INLINE static Uint16Array* Cast(Value* obj);
  
   private:
    Uint16Array();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of Int16Array constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Int16Array : public TypedArray {
   public:
    static Local<Int16Array> New(Local<ArrayBuffer> array_buffer,
                                 size_t byte_offset, size_t length);
    static Local<Int16Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                 size_t byte_offset, size_t length);
    V8_INLINE static Int16Array* Cast(Value* obj);
  
   private:
    Int16Array();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of Uint32Array constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Uint32Array : public TypedArray {
   public:
    static Local<Uint32Array> New(Local<ArrayBuffer> array_buffer,
                                  size_t byte_offset, size_t length);
    static Local<Uint32Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                  size_t byte_offset, size_t length);
    V8_INLINE static Uint32Array* Cast(Value* obj);
  
   private:
    Uint32Array();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of Int32Array constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Int32Array : public TypedArray {
   public:
    static Local<Int32Array> New(Local<ArrayBuffer> array_buffer,
                                 size_t byte_offset, size_t length);
    static Local<Int32Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                 size_t byte_offset, size_t length);
    V8_INLINE static Int32Array* Cast(Value* obj);
  
   private:
    Int32Array();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of Float32Array constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Float32Array : public TypedArray {
   public:
    static Local<Float32Array> New(Local<ArrayBuffer> array_buffer,
                                   size_t byte_offset, size_t length);
    static Local<Float32Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                   size_t byte_offset, size_t length);
    V8_INLINE static Float32Array* Cast(Value* obj);
  
   private:
    Float32Array();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of Float64Array constructor (ES6 draft 15.13.6).
   */
  class V8_EXPORT Float64Array : public TypedArray {
   public:
    static Local<Float64Array> New(Local<ArrayBuffer> array_buffer,
                                   size_t byte_offset, size_t length);
    static Local<Float64Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                   size_t byte_offset, size_t length);
    V8_INLINE static Float64Array* Cast(Value* obj);
  
   private:
    Float64Array();
    static void CheckCast(Value* obj);
  };
  
  /**
   * An instance of BigInt64Array constructor.
   */
  class V8_EXPORT BigInt64Array : public TypedArray {
   public:
    static Local<BigInt64Array> New(Local<ArrayBuffer> array_buffer,
                                    size_t byte_offset, size_t length);
    static Local<BigInt64Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                    size_t byte_offset, size_t length);
    V8_INLINE static BigInt64Array* Cast(Value* obj);
  
   private:
    BigInt64Array();
    static void CheckCast(Value* obj);
  };
  
  /**
   * An instance of BigUint64Array constructor.
   */
  class V8_EXPORT BigUint64Array : public TypedArray {
   public:
    static Local<BigUint64Array> New(Local<ArrayBuffer> array_buffer,
                                     size_t byte_offset, size_t length);
    static Local<BigUint64Array> New(Local<SharedArrayBuffer> shared_array_buffer,
                                     size_t byte_offset, size_t length);
    V8_INLINE static BigUint64Array* Cast(Value* obj);
  
   private:
    BigUint64Array();
    static void CheckCast(Value* obj);
  };
  
  /**
   * An instance of DataView constructor (ES6 draft 15.13.7).
   */
  class V8_EXPORT DataView : public ArrayBufferView {
   public:
    static Local<DataView> New(Local<ArrayBuffer> array_buffer,
                               size_t byte_offset, size_t length);
    static Local<DataView> New(Local<SharedArrayBuffer> shared_array_buffer,
                               size_t byte_offset, size_t length);
    V8_INLINE static DataView* Cast(Value* obj);
  
   private:
    DataView();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of the built-in SharedArrayBuffer constructor.
   * This API is experimental and may change significantly.
   */
  class V8_EXPORT SharedArrayBuffer : public Object {
   public:
    /**
     * The contents of an |SharedArrayBuffer|. Externalization of
     * |SharedArrayBuffer| returns an instance of this class, populated, with a
     * pointer to data and byte length.
     *
     * The Data pointer of ArrayBuffer::Contents must be freed using the provided
     * deleter, which will call ArrayBuffer::Allocator::Free if the buffer
     * was allocated with ArraryBuffer::Allocator::Allocate.
     *
     * This API is experimental and may change significantly.
     */
    class V8_EXPORT Contents {  // NOLINT
     public:
      using Allocator = v8::ArrayBuffer::Allocator;
      using DeleterCallback = void (*)(void* buffer, size_t length, void* info);
  
      Contents()
          : data_(nullptr),
            byte_length_(0),
            allocation_base_(nullptr),
            allocation_length_(0),
            allocation_mode_(Allocator::AllocationMode::kNormal),
            deleter_(nullptr),
            deleter_data_(nullptr) {}
  
      void* AllocationBase() const { return allocation_base_; }
      size_t AllocationLength() const { return allocation_length_; }
      Allocator::AllocationMode AllocationMode() const {
        return allocation_mode_;
      }
  
      void* Data() const { return data_; }
      size_t ByteLength() const { return byte_length_; }
      DeleterCallback Deleter() const { return deleter_; }
      void* DeleterData() const { return deleter_data_; }
  
     private:
      Contents(void* data, size_t byte_length, void* allocation_base,
               size_t allocation_length,
               Allocator::AllocationMode allocation_mode, DeleterCallback deleter,
               void* deleter_data);
  
      void* data_;
      size_t byte_length_;
      void* allocation_base_;
      size_t allocation_length_;
      Allocator::AllocationMode allocation_mode_;
      DeleterCallback deleter_;
      void* deleter_data_;
  
      friend class SharedArrayBuffer;
    };
  
    /**
     * Data length in bytes.
     */
    size_t ByteLength() const;
  
    /**
     * Create a new SharedArrayBuffer. Allocate |byte_length| bytes.
     * Allocated memory will be owned by a created SharedArrayBuffer and
     * will be deallocated when it is garbage-collected,
     * unless the object is externalized.
     */
    static Local<SharedArrayBuffer> New(Isolate* isolate, size_t byte_length);
  
    /**
     * Create a new SharedArrayBuffer over an existing memory block.  The created
     * array buffer is immediately in externalized state unless otherwise
     * specified. The memory block will not be reclaimed when a created
     * SharedArrayBuffer is garbage-collected.
     */
    static Local<SharedArrayBuffer> New(
        Isolate* isolate, void* data, size_t byte_length,
        ArrayBufferCreationMode mode = ArrayBufferCreationMode::kExternalized);
  
    /**
     * Create a new SharedArrayBuffer over an existing memory block. Propagate
     * flags to indicate whether the underlying buffer can be grown.
     */
    V8_DEPRECATED("Use New method with data, and byte_length instead.",
                  static Local<SharedArrayBuffer> New(
                      Isolate* isolate, const SharedArrayBuffer::Contents&,
                      ArrayBufferCreationMode mode =
                          ArrayBufferCreationMode::kExternalized));
  
    /**
     * Returns true if SharedArrayBuffer is externalized, that is, does not
     * own its memory block.
     */
    bool IsExternal() const;
  
    /**
     * Make this SharedArrayBuffer external. The pointer to underlying memory
     * block and byte length are returned as |Contents| structure. After
     * SharedArrayBuffer had been externalized, it does no longer own the memory
     * block. The caller should take steps to free memory when it is no longer
     * needed.
     *
     * The memory block is guaranteed to be allocated with |Allocator::Allocate|
     * by the allocator specified in
     * v8::Isolate::CreateParams::array_buffer_allocator.
     *
     */
    Contents Externalize();
  
    /**
     * Get a pointer to the ArrayBuffer's underlying memory block without
     * externalizing it. If the ArrayBuffer is not externalized, this pointer
     * will become invalid as soon as the ArrayBuffer became garbage collected.
     *
     * The embedder should make sure to hold a strong reference to the
     * ArrayBuffer while accessing this pointer.
     *
     * The memory block is guaranteed to be allocated with |Allocator::Allocate|
     * by the allocator specified in
     * v8::Isolate::CreateParams::array_buffer_allocator.
     */
    Contents GetContents();
  
    V8_INLINE static SharedArrayBuffer* Cast(Value* obj);
  
    static const int kInternalFieldCount = V8_ARRAY_BUFFER_INTERNAL_FIELD_COUNT;
  
   private:
    SharedArrayBuffer();
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of the built-in Date constructor (ECMA-262, 15.9).
   */
  class V8_EXPORT Date : public Object {
   public:
    static V8_WARN_UNUSED_RESULT MaybeLocal<Value> New(Local<Context> context,
                                                       double time);
  
    /**
     * A specialization of Value::NumberValue that is more efficient
     * because we know the structure of this object.
     */
    double ValueOf() const;
  
    V8_INLINE static Date* Cast(Value* obj);
  
   private:
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * A Number object (ECMA-262, 4.3.21).
   */
  class V8_EXPORT NumberObject : public Object {
   public:
    static Local<Value> New(Isolate* isolate, double value);
  
    double ValueOf() const;
  
    V8_INLINE static NumberObject* Cast(Value* obj);
  
   private:
    static void CheckCast(Value* obj);
  };
  
  /**
   * A BigInt object (https://tc39.github.io/proposal-bigint)
   */
  class V8_EXPORT BigIntObject : public Object {
   public:
    static Local<Value> New(Isolate* isolate, int64_t value);
  
    Local<BigInt> ValueOf() const;
  
    V8_INLINE static BigIntObject* Cast(Value* obj);
  
   private:
    static void CheckCast(Value* obj);
  };
  
  /**
   * A Boolean object (ECMA-262, 4.3.15).
   */
  class V8_EXPORT BooleanObject : public Object {
   public:
    static Local<Value> New(Isolate* isolate, bool value);
  
    bool ValueOf() const;
  
    V8_INLINE static BooleanObject* Cast(Value* obj);
  
   private:
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * A String object (ECMA-262, 4.3.18).
   */
  class V8_EXPORT StringObject : public Object {
   public:
    static Local<Value> New(Isolate* isolate, Local<String> value);
  
    Local<String> ValueOf() const;
  
    V8_INLINE static StringObject* Cast(Value* obj);
  
   private:
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * A Symbol object (ECMA-262 edition 6).
   */
  class V8_EXPORT SymbolObject : public Object {
   public:
    static Local<Value> New(Isolate* isolate, Local<Symbol> value);
  
    Local<Symbol> ValueOf() const;
  
    V8_INLINE static SymbolObject* Cast(Value* obj);
  
   private:
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * An instance of the built-in RegExp constructor (ECMA-262, 15.10).
   */
  class V8_EXPORT RegExp : public Object {
   public:
    /**
     * Regular expression flag bits. They can be or'ed to enable a set
     * of flags.
     */
    enum Flags {
      kNone = 0,
      kGlobal = 1 << 0,
      kIgnoreCase = 1 << 1,
      kMultiline = 1 << 2,
      kSticky = 1 << 3,
      kUnicode = 1 << 4,
      kDotAll = 1 << 5,
    };
  
    /**
     * Creates a regular expression from the given pattern string and
     * the flags bit field. May throw a JavaScript exception as
     * described in ECMA-262, 15.10.4.1.
     *
     * For example,
     *   RegExp::New(v8::String::New("foo"),
     *               static_cast<RegExp::Flags>(kGlobal | kMultiline))
     * is equivalent to evaluating "/foo/gm".
     */
    static V8_WARN_UNUSED_RESULT MaybeLocal<RegExp> New(Local<Context> context,
                                                        Local<String> pattern,
                                                        Flags flags);
  
    /**
     * Returns the value of the source property: a string representing
     * the regular expression.
     */
    Local<String> GetSource() const;
  
    /**
     * Returns the flags bit field.
     */
    Flags GetFlags() const;
  
    V8_INLINE static RegExp* Cast(Value* obj);
  
   private:
    static void CheckCast(Value* obj);
  };
  
  
  /**
   * A JavaScript value that wraps a C++ void*. This type of value is mainly used
   * to associate C++ data structures with JavaScript objects.
   */
  class V8_EXPORT External : public Value {
   public:
    static Local<External> New(Isolate* isolate, void* value);
    V8_INLINE static External* Cast(Value* obj);
    void* Value() const;
   private:
    static void CheckCast(v8::Value* obj);
  };
  
  #define V8_INTRINSICS_LIST(F)                    \
    F(ArrayProto_entries, array_entries_iterator)  \
    F(ArrayProto_forEach, array_for_each_iterator) \
    F(ArrayProto_keys, array_keys_iterator)        \
    F(ArrayProto_values, array_values_iterator)    \
    F(ErrorPrototype, initial_error_prototype)     \
    F(IteratorPrototype, initial_iterator_prototype)
  
  enum Intrinsic {
  #define V8_DECL_INTRINSIC(name, iname) k##name,
    V8_INTRINSICS_LIST(V8_DECL_INTRINSIC)
  #undef V8_DECL_INTRINSIC
  };
  
  
  // --- Templates ---
  
  
  /**
   * The superclass of object and function templates.
   */
  class V8_EXPORT Template : public Data {
   public:
    /**
     * Adds a property to each instance created by this template.
     *
     * The property must be defined either as a primitive value, or a template.
     */
    void Set(Local<Name> name, Local<Data> value,
             PropertyAttribute attributes = None);
    void SetPrivate(Local<Private> name, Local<Data> value,
                    PropertyAttribute attributes = None);
    V8_INLINE void Set(Isolate* isolate, const char* name, Local<Data> value);
  
    void SetAccessorProperty(
       Local<Name> name,
       Local<FunctionTemplate> getter = Local<FunctionTemplate>(),
       Local<FunctionTemplate> setter = Local<FunctionTemplate>(),
       PropertyAttribute attribute = None,
       AccessControl settings = DEFAULT);
  
    /**
     * Whenever the property with the given name is accessed on objects
     * created from this Template the getter and setter callbacks
     * are called instead of getting and setting the property directly
     * on the JavaScript object.
     *
     * \param name The name of the property for which an accessor is added.
     * \param getter The callback to invoke when getting the property.
     * \param setter The callback to invoke when setting the property.
     * \param data A piece of data that will be passed to the getter and setter
     *   callbacks whenever they are invoked.
     * \param settings Access control settings for the accessor. This is a bit
     *   field consisting of one of more of
     *   DEFAULT = 0, ALL_CAN_READ = 1, or ALL_CAN_WRITE = 2.
     *   The default is to not allow cross-context access.
     *   ALL_CAN_READ means that all cross-context reads are allowed.
     *   ALL_CAN_WRITE means that all cross-context writes are allowed.
     *   The combination ALL_CAN_READ | ALL_CAN_WRITE can be used to allow all
     *   cross-context access.
     * \param attribute The attributes of the property for which an accessor
     *   is added.
     * \param signature The signature describes valid receivers for the accessor
     *   and is used to perform implicit instance checks against them. If the
     *   receiver is incompatible (i.e. is not an instance of the constructor as
     *   defined by FunctionTemplate::HasInstance()), an implicit TypeError is
     *   thrown and no callback is invoked.
     */
    void SetNativeDataProperty(
        Local<String> name, AccessorGetterCallback getter,
        AccessorSetterCallback setter = nullptr,
        // TODO(dcarney): gcc can't handle Local below
        Local<Value> data = Local<Value>(), PropertyAttribute attribute = None,
        Local<AccessorSignature> signature = Local<AccessorSignature>(),
        AccessControl settings = DEFAULT,
        SideEffectType getter_side_effect_type = SideEffectType::kHasSideEffect,
        SideEffectType setter_side_effect_type = SideEffectType::kHasSideEffect);
    void SetNativeDataProperty(
        Local<Name> name, AccessorNameGetterCallback getter,
        AccessorNameSetterCallback setter = nullptr,
        // TODO(dcarney): gcc can't handle Local below
        Local<Value> data = Local<Value>(), PropertyAttribute attribute = None,
        Local<AccessorSignature> signature = Local<AccessorSignature>(),
        AccessControl settings = DEFAULT,
        SideEffectType getter_side_effect_type = SideEffectType::kHasSideEffect,
        SideEffectType setter_side_effect_type = SideEffectType::kHasSideEffect);
  
    /**
     * Like SetNativeDataProperty, but V8 will replace the native data property
     * with a real data property on first access.
     */
    void SetLazyDataProperty(
        Local<Name> name, AccessorNameGetterCallback getter,
        Local<Value> data = Local<Value>(), PropertyAttribute attribute = None,
        SideEffectType getter_side_effect_type = SideEffectType::kHasSideEffect,
        SideEffectType setter_side_effect_type = SideEffectType::kHasSideEffect);
  
    /**
     * During template instantiation, sets the value with the intrinsic property
     * from the correct context.
     */
    void SetIntrinsicDataProperty(Local<Name> name, Intrinsic intrinsic,
                                  PropertyAttribute attribute = None);
  
   private:
    Template();
  
    friend class ObjectTemplate;
    friend class FunctionTemplate;
  };
  
  // TODO(dcarney): Replace GenericNamedPropertyFooCallback with just
  // NamedPropertyFooCallback.
  
  /**
   * Interceptor for get requests on an object.
   *
   * Use `info.GetReturnValue().Set()` to set the return value of the
   * intercepted get request.
   *
   * \param property The name of the property for which the request was
   * intercepted.
   * \param info Information about the intercepted request, such as
   * isolate, receiver, return value, or whether running in `'use strict`' mode.
   * See `PropertyCallbackInfo`.
   *
   * \code
   *  void GetterCallback(
   *    Local<Name> name,
   *    const v8::PropertyCallbackInfo<v8::Value>& info) {
   *      info.GetReturnValue().Set(v8_num(42));
   *  }
   *
   *  v8::Local<v8::FunctionTemplate> templ =
   *      v8::FunctionTemplate::New(isolate);
   *  templ->InstanceTemplate()->SetHandler(
   *      v8::NamedPropertyHandlerConfiguration(GetterCallback));
   *  LocalContext env;
   *  env->Global()
   *      ->Set(env.local(), v8_str("obj"), templ->GetFunction(env.local())
   *                                             .ToLocalChecked()
   *                                             ->NewInstance(env.local())
   *                                             .ToLocalChecked())
   *      .FromJust();
   *  v8::Local<v8::Value> result = CompileRun("obj.a = 17; obj.a");
   *  CHECK(v8_num(42)->Equals(env.local(), result).FromJust());
   * \endcode
   *
   * See also `ObjectTemplate::SetHandler`.
   */
  typedef void (*GenericNamedPropertyGetterCallback)(
      Local<Name> property, const PropertyCallbackInfo<Value>& info);
  
  /**
   * Interceptor for set requests on an object.
   *
   * Use `info.GetReturnValue()` to indicate whether the request was intercepted
   * or not. If the setter successfully intercepts the request, i.e., if the
   * request should not be further executed, call
   * `info.GetReturnValue().Set(value)`. If the setter
   * did not intercept the request, i.e., if the request should be handled as
   * if no interceptor is present, do not not call `Set()`.
   *
   * \param property The name of the property for which the request was
   * intercepted.
   * \param value The value which the property will have if the request
   * is not intercepted.
   * \param info Information about the intercepted request, such as
   * isolate, receiver, return value, or whether running in `'use strict'` mode.
   * See `PropertyCallbackInfo`.
   *
   * See also
   * `ObjectTemplate::SetHandler.`
   */
  typedef void (*GenericNamedPropertySetterCallback)(
      Local<Name> property, Local<Value> value,
      const PropertyCallbackInfo<Value>& info);
  
  /**
   * Intercepts all requests that query the attributes of the
   * property, e.g., getOwnPropertyDescriptor(), propertyIsEnumerable(), and
   * defineProperty().
   *
   * Use `info.GetReturnValue().Set(value)` to set the property attributes. The
   * value is an integer encoding a `v8::PropertyAttribute`.
   *
   * \param property The name of the property for which the request was
   * intercepted.
   * \param info Information about the intercepted request, such as
   * isolate, receiver, return value, or whether running in `'use strict'` mode.
   * See `PropertyCallbackInfo`.
   *
   * \note Some functions query the property attributes internally, even though
   * they do not return the attributes. For example, `hasOwnProperty()` can
   * trigger this interceptor depending on the state of the object.
   *
   * See also
   * `ObjectTemplate::SetHandler.`
   */
  typedef void (*GenericNamedPropertyQueryCallback)(
      Local<Name> property, const PropertyCallbackInfo<Integer>& info);
  
  /**
   * Interceptor for delete requests on an object.
   *
   * Use `info.GetReturnValue()` to indicate whether the request was intercepted
   * or not. If the deleter successfully intercepts the request, i.e., if the
   * request should not be further executed, call
   * `info.GetReturnValue().Set(value)` with a boolean `value`. The `value` is
   * used as the return value of `delete`.
   *
   * \param property The name of the property for which the request was
   * intercepted.
   * \param info Information about the intercepted request, such as
   * isolate, receiver, return value, or whether running in `'use strict'` mode.
   * See `PropertyCallbackInfo`.
   *
   * \note If you need to mimic the behavior of `delete`, i.e., throw in strict
   * mode instead of returning false, use `info.ShouldThrowOnError()` to determine
   * if you are in strict mode.
   *
   * See also `ObjectTemplate::SetHandler.`
   */
  typedef void (*GenericNamedPropertyDeleterCallback)(
      Local<Name> property, const PropertyCallbackInfo<Boolean>& info);
  
  /**
   * Returns an array containing the names of the properties the named
   * property getter intercepts.
   *
   * Note: The values in the array must be of type v8::Name.
   */
  typedef void (*GenericNamedPropertyEnumeratorCallback)(
      const PropertyCallbackInfo<Array>& info);
  
  /**
   * Interceptor for defineProperty requests on an object.
   *
   * Use `info.GetReturnValue()` to indicate whether the request was intercepted
   * or not. If the definer successfully intercepts the request, i.e., if the
   * request should not be further executed, call
   * `info.GetReturnValue().Set(value)`. If the definer
   * did not intercept the request, i.e., if the request should be handled as
   * if no interceptor is present, do not not call `Set()`.
   *
   * \param property The name of the property for which the request was
   * intercepted.
   * \param desc The property descriptor which is used to define the
   * property if the request is not intercepted.
   * \param info Information about the intercepted request, such as
   * isolate, receiver, return value, or whether running in `'use strict'` mode.
   * See `PropertyCallbackInfo`.
   *
   * See also `ObjectTemplate::SetHandler`.
   */
  typedef void (*GenericNamedPropertyDefinerCallback)(
      Local<Name> property, const PropertyDescriptor& desc,
      const PropertyCallbackInfo<Value>& info);
  
  /**
   * Interceptor for getOwnPropertyDescriptor requests on an object.
   *
   * Use `info.GetReturnValue().Set()` to set the return value of the
   * intercepted request. The return value must be an object that
   * can be converted to a PropertyDescriptor, e.g., a `v8::value` returned from
   * `v8::Object::getOwnPropertyDescriptor`.
   *
   * \param property The name of the property for which the request was
   * intercepted.
   * \info Information about the intercepted request, such as
   * isolate, receiver, return value, or whether running in `'use strict'` mode.
   * See `PropertyCallbackInfo`.
   *
   * \note If GetOwnPropertyDescriptor is intercepted, it will
   * always return true, i.e., indicate that the property was found.
   *
   * See also `ObjectTemplate::SetHandler`.
   */
  typedef void (*GenericNamedPropertyDescriptorCallback)(
      Local<Name> property, const PropertyCallbackInfo<Value>& info);
  
  /**
   * See `v8::GenericNamedPropertyGetterCallback`.
   */
  typedef void (*IndexedPropertyGetterCallback)(
      uint32_t index,
      const PropertyCallbackInfo<Value>& info);
  
  /**
   * See `v8::GenericNamedPropertySetterCallback`.
   */
  typedef void (*IndexedPropertySetterCallback)(
      uint32_t index,
      Local<Value> value,
      const PropertyCallbackInfo<Value>& info);
  
  /**
   * See `v8::GenericNamedPropertyQueryCallback`.
   */
  typedef void (*IndexedPropertyQueryCallback)(
      uint32_t index,
      const PropertyCallbackInfo<Integer>& info);
  
  /**
   * See `v8::GenericNamedPropertyDeleterCallback`.
   */
  typedef void (*IndexedPropertyDeleterCallback)(
      uint32_t index,
      const PropertyCallbackInfo<Boolean>& info);
  
  /**
   * Returns an array containing the indices of the properties the indexed
   * property getter intercepts.
   *
   * Note: The values in the array must be uint32_t.
   */
  typedef void (*IndexedPropertyEnumeratorCallback)(
      const PropertyCallbackInfo<Array>& info);
  
  /**
   * See `v8::GenericNamedPropertyDefinerCallback`.
   */
  typedef void (*IndexedPropertyDefinerCallback)(
      uint32_t index, const PropertyDescriptor& desc,
      const PropertyCallbackInfo<Value>& info);
  
  /**
   * See `v8::GenericNamedPropertyDescriptorCallback`.
   */
  typedef void (*IndexedPropertyDescriptorCallback)(
      uint32_t index, const PropertyCallbackInfo<Value>& info);
  
  /**
   * Access type specification.
   */
  enum AccessType {
    ACCESS_GET,
    ACCESS_SET,
    ACCESS_HAS,
    ACCESS_DELETE,
    ACCESS_KEYS
  };
  
  
  /**
   * Returns true if the given context should be allowed to access the given
   * object.
   */
  typedef bool (*AccessCheckCallback)(Local<Context> accessing_context,
                                      Local<Object> accessed_object,
                                      Local<Value> data);
  
  /**
   * A FunctionTemplate is used to create functions at runtime. There
   * can only be one function created from a FunctionTemplate in a
   * context.  The lifetime of the created function is equal to the
   * lifetime of the context.  So in case the embedder needs to create
   * temporary functions that can be collected using Scripts is
   * preferred.
   *
   * Any modification of a FunctionTemplate after first instantiation will trigger
   * a crash.
   *
   * A FunctionTemplate can have properties, these properties are added to the
   * function object when it is created.
   *
   * A FunctionTemplate has a corresponding instance template which is
   * used to create object instances when the function is used as a
   * constructor. Properties added to the instance template are added to
   * each object instance.
   *
   * A FunctionTemplate can have a prototype template. The prototype template
   * is used to create the prototype object of the function.
   *
   * The following example shows how to use a FunctionTemplate:
   *
   * \code
   *    v8::Local<v8::FunctionTemplate> t = v8::FunctionTemplate::New(isolate);
   *    t->Set(isolate, "func_property", v8::Number::New(isolate, 1));
   *
   *    v8::Local<v8::Template> proto_t = t->PrototypeTemplate();
   *    proto_t->Set(isolate,
   *                 "proto_method",
   *                 v8::FunctionTemplate::New(isolate, InvokeCallback));
   *    proto_t->Set(isolate, "proto_const", v8::Number::New(isolate, 2));
   *
   *    v8::Local<v8::ObjectTemplate> instance_t = t->InstanceTemplate();
   *    instance_t->SetAccessor(String::NewFromUtf8(isolate, "instance_accessor"),
   *                            InstanceAccessorCallback);
   *    instance_t->SetHandler(
   *        NamedPropertyHandlerConfiguration(PropertyHandlerCallback));
   *    instance_t->Set(String::NewFromUtf8(isolate, "instance_property"),
   *                    Number::New(isolate, 3));
   *
   *    v8::Local<v8::Function> function = t->GetFunction();
   *    v8::Local<v8::Object> instance = function->NewInstance();
   * \endcode
   *
   * Let's use "function" as the JS variable name of the function object
   * and "instance" for the instance object created above.  The function
   * and the instance will have the following properties:
   *
   * \code
   *   func_property in function == true;
   *   function.func_property == 1;
   *
   *   function.prototype.proto_method() invokes 'InvokeCallback'
   *   function.prototype.proto_const == 2;
   *
   *   instance instanceof function == true;
   *   instance.instance_accessor calls 'InstanceAccessorCallback'
   *   instance.instance_property == 3;
   * \endcode
   *
   * A FunctionTemplate can inherit from another one by calling the
   * FunctionTemplate::Inherit method.  The following graph illustrates
   * the semantics of inheritance:
   *
   * \code
   *   FunctionTemplate Parent  -> Parent() . prototype -> { }
   *     ^                                                  ^
   *     | Inherit(Parent)                                  | .__proto__
   *     |                                                  |
   *   FunctionTemplate Child   -> Child()  . prototype -> { }
   * \endcode
   *
   * A FunctionTemplate 'Child' inherits from 'Parent', the prototype
   * object of the Child() function has __proto__ pointing to the
   * Parent() function's prototype object. An instance of the Child
   * function has all properties on Parent's instance templates.
   *
   * Let Parent be the FunctionTemplate initialized in the previous
   * section and create a Child FunctionTemplate by:
   *
   * \code
   *   Local<FunctionTemplate> parent = t;
   *   Local<FunctionTemplate> child = FunctionTemplate::New();
   *   child->Inherit(parent);
   *
   *   Local<Function> child_function = child->GetFunction();
   *   Local<Object> child_instance = child_function->NewInstance();
   * \endcode
   *
   * The Child function and Child instance will have the following
   * properties:
   *
   * \code
   *   child_func.prototype.__proto__ == function.prototype;
   *   child_instance.instance_accessor calls 'InstanceAccessorCallback'
   *   child_instance.instance_property == 3;
   * \endcode
   */
  class V8_EXPORT FunctionTemplate : public Template {
   public:
    /** Creates a function template.*/
    static Local<FunctionTemplate> New(
        Isolate* isolate, FunctionCallback callback = nullptr,
        Local<Value> data = Local<Value>(),
        Local<Signature> signature = Local<Signature>(), int length = 0,
        ConstructorBehavior behavior = ConstructorBehavior::kAllow,
        SideEffectType side_effect_type = SideEffectType::kHasSideEffect);
  
    /** Get a template included in the snapshot by index. */
    static MaybeLocal<FunctionTemplate> FromSnapshot(Isolate* isolate,
                                                     size_t index);
  
    /**
     * Creates a function template backed/cached by a private property.
     */
    static Local<FunctionTemplate> NewWithCache(
        Isolate* isolate, FunctionCallback callback,
        Local<Private> cache_property, Local<Value> data = Local<Value>(),
        Local<Signature> signature = Local<Signature>(), int length = 0,
        SideEffectType side_effect_type = SideEffectType::kHasSideEffect);
  
    /** Returns the unique function instance in the current execution context.*/
    V8_WARN_UNUSED_RESULT MaybeLocal<Function> GetFunction(
        Local<Context> context);
  
    /**
     * Similar to Context::NewRemoteContext, this creates an instance that
     * isn't backed by an actual object.
     *
     * The InstanceTemplate of this FunctionTemplate must have access checks with
     * handlers installed.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Object> NewRemoteInstance();
  
    /**
     * Set the call-handler callback for a FunctionTemplate.  This
     * callback is called whenever the function created from this
     * FunctionTemplate is called.
     */
    void SetCallHandler(
        FunctionCallback callback, Local<Value> data = Local<Value>(),
        SideEffectType side_effect_type = SideEffectType::kHasSideEffect);
  
    /** Set the predefined length property for the FunctionTemplate. */
    void SetLength(int length);
  
    /** Get the InstanceTemplate. */
    Local<ObjectTemplate> InstanceTemplate();
  
    /**
     * Causes the function template to inherit from a parent function template.
     * This means the function's prototype.__proto__ is set to the parent
     * function's prototype.
     **/
    void Inherit(Local<FunctionTemplate> parent);
  
    /**
     * A PrototypeTemplate is the template used to create the prototype object
     * of the function created by this template.
     */
    Local<ObjectTemplate> PrototypeTemplate();
  
    /**
     * A PrototypeProviderTemplate is another function template whose prototype
     * property is used for this template. This is mutually exclusive with setting
     * a prototype template indirectly by calling PrototypeTemplate() or using
     * Inherit().
     **/
    void SetPrototypeProviderTemplate(Local<FunctionTemplate> prototype_provider);
  
    /**
     * Set the class name of the FunctionTemplate.  This is used for
     * printing objects created with the function created from the
     * FunctionTemplate as its constructor.
     */
    void SetClassName(Local<String> name);
  
  
    /**
     * When set to true, no access check will be performed on the receiver of a
     * function call.  Currently defaults to true, but this is subject to change.
     */
    void SetAcceptAnyReceiver(bool value);
  
    /**
     * Sets the ReadOnly flag in the attributes of the 'prototype' property
     * of functions created from this FunctionTemplate to true.
     */
    void ReadOnlyPrototype();
  
    /**
     * Removes the prototype property from functions created from this
     * FunctionTemplate.
     */
    void RemovePrototype();
  
    /**
     * Returns true if the given object is an instance of this function
     * template.
     */
    bool HasInstance(Local<Value> object);
  
    V8_INLINE static FunctionTemplate* Cast(Data* data);
  
   private:
    FunctionTemplate();
  
    static void CheckCast(Data* that);
    friend class Context;
    friend class ObjectTemplate;
  };
  
  /**
   * Configuration flags for v8::NamedPropertyHandlerConfiguration or
   * v8::IndexedPropertyHandlerConfiguration.
   */
  enum class PropertyHandlerFlags {
    /**
     * None.
     */
    kNone = 0,
  
    /**
     * See ALL_CAN_READ above.
     */
    kAllCanRead = 1,
  
    /** Will not call into interceptor for properties on the receiver or prototype
     * chain, i.e., only call into interceptor for properties that do not exist.
     * Currently only valid for named interceptors.
     */
    kNonMasking = 1 << 1,
  
    /**
     * Will not call into interceptor for symbol lookup.  Only meaningful for
     * named interceptors.
     */
    kOnlyInterceptStrings = 1 << 2,
  
    /**
     * The getter, query, enumerator callbacks do not produce side effects.
     */
    kHasNoSideEffect = 1 << 3,
  };
  
  struct NamedPropertyHandlerConfiguration {
    NamedPropertyHandlerConfiguration(
        GenericNamedPropertyGetterCallback getter,
        GenericNamedPropertySetterCallback setter,
        GenericNamedPropertyQueryCallback query,
        GenericNamedPropertyDeleterCallback deleter,
        GenericNamedPropertyEnumeratorCallback enumerator,
        GenericNamedPropertyDefinerCallback definer,
        GenericNamedPropertyDescriptorCallback descriptor,
        Local<Value> data = Local<Value>(),
        PropertyHandlerFlags flags = PropertyHandlerFlags::kNone)
        : getter(getter),
          setter(setter),
          query(query),
          deleter(deleter),
          enumerator(enumerator),
          definer(definer),
          descriptor(descriptor),
          data(data),
          flags(flags) {}
  
    NamedPropertyHandlerConfiguration(
        /** Note: getter is required */
        GenericNamedPropertyGetterCallback getter = nullptr,
        GenericNamedPropertySetterCallback setter = nullptr,
        GenericNamedPropertyQueryCallback query = nullptr,
        GenericNamedPropertyDeleterCallback deleter = nullptr,
        GenericNamedPropertyEnumeratorCallback enumerator = nullptr,
        Local<Value> data = Local<Value>(),
        PropertyHandlerFlags flags = PropertyHandlerFlags::kNone)
        : getter(getter),
          setter(setter),
          query(query),
          deleter(deleter),
          enumerator(enumerator),
          definer(nullptr),
          descriptor(nullptr),
          data(data),
          flags(flags) {}
  
    NamedPropertyHandlerConfiguration(
        GenericNamedPropertyGetterCallback getter,
        GenericNamedPropertySetterCallback setter,
        GenericNamedPropertyDescriptorCallback descriptor,
        GenericNamedPropertyDeleterCallback deleter,
        GenericNamedPropertyEnumeratorCallback enumerator,
        GenericNamedPropertyDefinerCallback definer,
        Local<Value> data = Local<Value>(),
        PropertyHandlerFlags flags = PropertyHandlerFlags::kNone)
        : getter(getter),
          setter(setter),
          query(nullptr),
          deleter(deleter),
          enumerator(enumerator),
          definer(definer),
          descriptor(descriptor),
          data(data),
          flags(flags) {}
  
    GenericNamedPropertyGetterCallback getter;
    GenericNamedPropertySetterCallback setter;
    GenericNamedPropertyQueryCallback query;
    GenericNamedPropertyDeleterCallback deleter;
    GenericNamedPropertyEnumeratorCallback enumerator;
    GenericNamedPropertyDefinerCallback definer;
    GenericNamedPropertyDescriptorCallback descriptor;
    Local<Value> data;
    PropertyHandlerFlags flags;
  };
  
  
  struct IndexedPropertyHandlerConfiguration {
    IndexedPropertyHandlerConfiguration(
        IndexedPropertyGetterCallback getter,
        IndexedPropertySetterCallback setter, IndexedPropertyQueryCallback query,
        IndexedPropertyDeleterCallback deleter,
        IndexedPropertyEnumeratorCallback enumerator,
        IndexedPropertyDefinerCallback definer,
        IndexedPropertyDescriptorCallback descriptor,
        Local<Value> data = Local<Value>(),
        PropertyHandlerFlags flags = PropertyHandlerFlags::kNone)
        : getter(getter),
          setter(setter),
          query(query),
          deleter(deleter),
          enumerator(enumerator),
          definer(definer),
          descriptor(descriptor),
          data(data),
          flags(flags) {}
  
    IndexedPropertyHandlerConfiguration(
        /** Note: getter is required */
        IndexedPropertyGetterCallback getter = nullptr,
        IndexedPropertySetterCallback setter = nullptr,
        IndexedPropertyQueryCallback query = nullptr,
        IndexedPropertyDeleterCallback deleter = nullptr,
        IndexedPropertyEnumeratorCallback enumerator = nullptr,
        Local<Value> data = Local<Value>(),
        PropertyHandlerFlags flags = PropertyHandlerFlags::kNone)
        : getter(getter),
          setter(setter),
          query(query),
          deleter(deleter),
          enumerator(enumerator),
          definer(nullptr),
          descriptor(nullptr),
          data(data),
          flags(flags) {}
  
    IndexedPropertyHandlerConfiguration(
        IndexedPropertyGetterCallback getter,
        IndexedPropertySetterCallback setter,
        IndexedPropertyDescriptorCallback descriptor,
        IndexedPropertyDeleterCallback deleter,
        IndexedPropertyEnumeratorCallback enumerator,
        IndexedPropertyDefinerCallback definer,
        Local<Value> data = Local<Value>(),
        PropertyHandlerFlags flags = PropertyHandlerFlags::kNone)
        : getter(getter),
          setter(setter),
          query(nullptr),
          deleter(deleter),
          enumerator(enumerator),
          definer(definer),
          descriptor(descriptor),
          data(data),
          flags(flags) {}
  
    IndexedPropertyGetterCallback getter;
    IndexedPropertySetterCallback setter;
    IndexedPropertyQueryCallback query;
    IndexedPropertyDeleterCallback deleter;
    IndexedPropertyEnumeratorCallback enumerator;
    IndexedPropertyDefinerCallback definer;
    IndexedPropertyDescriptorCallback descriptor;
    Local<Value> data;
    PropertyHandlerFlags flags;
  };
  
  
  /**
   * An ObjectTemplate is used to create objects at runtime.
   *
   * Properties added to an ObjectTemplate are added to each object
   * created from the ObjectTemplate.
   */
  class V8_EXPORT ObjectTemplate : public Template {
   public:
    /** Creates an ObjectTemplate. */
    static Local<ObjectTemplate> New(
        Isolate* isolate,
        Local<FunctionTemplate> constructor = Local<FunctionTemplate>());
  
    /** Get a template included in the snapshot by index. */
    static MaybeLocal<ObjectTemplate> FromSnapshot(Isolate* isolate,
                                                   size_t index);
  
    /** Creates a new instance of this template.*/
    V8_WARN_UNUSED_RESULT MaybeLocal<Object> NewInstance(Local<Context> context);
  
    /**
     * Sets an accessor on the object template.
     *
     * Whenever the property with the given name is accessed on objects
     * created from this ObjectTemplate the getter and setter callbacks
     * are called instead of getting and setting the property directly
     * on the JavaScript object.
     *
     * \param name The name of the property for which an accessor is added.
     * \param getter The callback to invoke when getting the property.
     * \param setter The callback to invoke when setting the property.
     * \param data A piece of data that will be passed to the getter and setter
     *   callbacks whenever they are invoked.
     * \param settings Access control settings for the accessor. This is a bit
     *   field consisting of one of more of
     *   DEFAULT = 0, ALL_CAN_READ = 1, or ALL_CAN_WRITE = 2.
     *   The default is to not allow cross-context access.
     *   ALL_CAN_READ means that all cross-context reads are allowed.
     *   ALL_CAN_WRITE means that all cross-context writes are allowed.
     *   The combination ALL_CAN_READ | ALL_CAN_WRITE can be used to allow all
     *   cross-context access.
     * \param attribute The attributes of the property for which an accessor
     *   is added.
     * \param signature The signature describes valid receivers for the accessor
     *   and is used to perform implicit instance checks against them. If the
     *   receiver is incompatible (i.e. is not an instance of the constructor as
     *   defined by FunctionTemplate::HasInstance()), an implicit TypeError is
     *   thrown and no callback is invoked.
     */
    void SetAccessor(
        Local<String> name, AccessorGetterCallback getter,
        AccessorSetterCallback setter = nullptr,
        Local<Value> data = Local<Value>(), AccessControl settings = DEFAULT,
        PropertyAttribute attribute = None,
        Local<AccessorSignature> signature = Local<AccessorSignature>(),
        SideEffectType getter_side_effect_type = SideEffectType::kHasSideEffect,
        SideEffectType setter_side_effect_type = SideEffectType::kHasSideEffect);
    void SetAccessor(
        Local<Name> name, AccessorNameGetterCallback getter,
        AccessorNameSetterCallback setter = nullptr,
        Local<Value> data = Local<Value>(), AccessControl settings = DEFAULT,
        PropertyAttribute attribute = None,
        Local<AccessorSignature> signature = Local<AccessorSignature>(),
        SideEffectType getter_side_effect_type = SideEffectType::kHasSideEffect,
        SideEffectType setter_side_effect_type = SideEffectType::kHasSideEffect);
  
    /**
     * Sets a named property handler on the object template.
     *
     * Whenever a property whose name is a string or a symbol is accessed on
     * objects created from this object template, the provided callback is
     * invoked instead of accessing the property directly on the JavaScript
     * object.
     *
     * @param configuration The NamedPropertyHandlerConfiguration that defines the
     * callbacks to invoke when accessing a property.
     */
    void SetHandler(const NamedPropertyHandlerConfiguration& configuration);
  
    /**
     * Sets an indexed property handler on the object template.
     *
     * Whenever an indexed property is accessed on objects created from
     * this object template, the provided callback is invoked instead of
     * accessing the property directly on the JavaScript object.
     *
     * \param getter The callback to invoke when getting a property.
     * \param setter The callback to invoke when setting a property.
     * \param query The callback to invoke to check if an object has a property.
     * \param deleter The callback to invoke when deleting a property.
     * \param enumerator The callback to invoke to enumerate all the indexed
     *   properties of an object.
     * \param data A piece of data that will be passed to the callbacks
     *   whenever they are invoked.
     */
    // TODO(dcarney): deprecate
    void SetIndexedPropertyHandler(
        IndexedPropertyGetterCallback getter,
        IndexedPropertySetterCallback setter = nullptr,
        IndexedPropertyQueryCallback query = nullptr,
        IndexedPropertyDeleterCallback deleter = nullptr,
        IndexedPropertyEnumeratorCallback enumerator = nullptr,
        Local<Value> data = Local<Value>()) {
      SetHandler(IndexedPropertyHandlerConfiguration(getter, setter, query,
                                                     deleter, enumerator, data));
    }
  
    /**
     * Sets an indexed property handler on the object template.
     *
     * Whenever an indexed property is accessed on objects created from
     * this object template, the provided callback is invoked instead of
     * accessing the property directly on the JavaScript object.
     *
     * @param configuration The IndexedPropertyHandlerConfiguration that defines
     * the callbacks to invoke when accessing a property.
     */
    void SetHandler(const IndexedPropertyHandlerConfiguration& configuration);
  
    /**
     * Sets the callback to be used when calling instances created from
     * this template as a function.  If no callback is set, instances
     * behave like normal JavaScript objects that cannot be called as a
     * function.
     */
    void SetCallAsFunctionHandler(FunctionCallback callback,
                                  Local<Value> data = Local<Value>());
  
    /**
     * Mark object instances of the template as undetectable.
     *
     * In many ways, undetectable objects behave as though they are not
     * there.  They behave like 'undefined' in conditionals and when
     * printed.  However, properties can be accessed and called as on
     * normal objects.
     */
    void MarkAsUndetectable();
  
    /**
     * Sets access check callback on the object template and enables access
     * checks.
     *
     * When accessing properties on instances of this object template,
     * the access check callback will be called to determine whether or
     * not to allow cross-context access to the properties.
     */
    void SetAccessCheckCallback(AccessCheckCallback callback,
                                Local<Value> data = Local<Value>());
  
    /**
     * Like SetAccessCheckCallback but invokes an interceptor on failed access
     * checks instead of looking up all-can-read properties. You can only use
     * either this method or SetAccessCheckCallback, but not both at the same
     * time.
     */
    void SetAccessCheckCallbackAndHandler(
        AccessCheckCallback callback,
        const NamedPropertyHandlerConfiguration& named_handler,
        const IndexedPropertyHandlerConfiguration& indexed_handler,
        Local<Value> data = Local<Value>());
  
    /**
     * Gets the number of internal fields for objects generated from
     * this template.
     */
    int InternalFieldCount();
  
    /**
     * Sets the number of internal fields for objects generated from
     * this template.
     */
    void SetInternalFieldCount(int value);
  
    /**
     * Returns true if the object will be an immutable prototype exotic object.
     */
    bool IsImmutableProto();
  
    /**
     * Makes the ObjectTemplate for an immutable prototype exotic object, with an
     * immutable __proto__.
     */
    void SetImmutableProto();
  
    V8_INLINE static ObjectTemplate* Cast(Data* data);
  
   private:
    ObjectTemplate();
    static Local<ObjectTemplate> New(internal::Isolate* isolate,
                                     Local<FunctionTemplate> constructor);
    static void CheckCast(Data* that);
    friend class FunctionTemplate;
  };
  
  /**
   * A Signature specifies which receiver is valid for a function.
   *
   * A receiver matches a given signature if the receiver (or any of its
   * hidden prototypes) was created from the signature's FunctionTemplate, or
   * from a FunctionTemplate that inherits directly or indirectly from the
   * signature's FunctionTemplate.
   */
  class V8_EXPORT Signature : public Data {
   public:
    static Local<Signature> New(
        Isolate* isolate,
        Local<FunctionTemplate> receiver = Local<FunctionTemplate>());
  
    V8_INLINE static Signature* Cast(Data* data);
  
   private:
    Signature();
  
    static void CheckCast(Data* that);
  };
  
  
  /**
   * An AccessorSignature specifies which receivers are valid parameters
   * to an accessor callback.
   */
  class V8_EXPORT AccessorSignature : public Data {
   public:
    static Local<AccessorSignature> New(
        Isolate* isolate,
        Local<FunctionTemplate> receiver = Local<FunctionTemplate>());
  
    V8_INLINE static AccessorSignature* Cast(Data* data);
  
   private:
    AccessorSignature();
  
    static void CheckCast(Data* that);
  };
  
  
  // --- Extensions ---
  
  /**
   * Ignore
   */
  class V8_EXPORT Extension {  // NOLINT
   public:
    // Note that the strings passed into this constructor must live as long
    // as the Extension itself.
    Extension(const char* name, const char* source = nullptr, int dep_count = 0,
              const char** deps = nullptr, int source_length = -1);
    virtual ~Extension() { delete source_; }
    virtual Local<FunctionTemplate> GetNativeFunctionTemplate(
        Isolate* isolate, Local<String> name) {
      return Local<FunctionTemplate>();
    }
  
    const char* name() const { return name_; }
    size_t source_length() const { return source_length_; }
    const String::ExternalOneByteStringResource* source() const {
      return source_;
    }
    int dependency_count() const { return dep_count_; }
    const char** dependencies() const { return deps_; }
    void set_auto_enable(bool value) { auto_enable_ = value; }
    bool auto_enable() { return auto_enable_; }
  
    // Disallow copying and assigning.
    Extension(const Extension&) = delete;
    void operator=(const Extension&) = delete;
  
   private:
    const char* name_;
    size_t source_length_;  // expected to initialize before source_
    String::ExternalOneByteStringResource* source_;
    int dep_count_;
    const char** deps_;
    bool auto_enable_;
  };
  
  void V8_EXPORT RegisterExtension(std::unique_ptr<Extension>);
  
  // --- Statics ---
  
  V8_INLINE Local<Primitive> Undefined(Isolate* isolate);
  V8_INLINE Local<Primitive> Null(Isolate* isolate);
  V8_INLINE Local<Boolean> True(Isolate* isolate);
  V8_INLINE Local<Boolean> False(Isolate* isolate);
  
  /**
   * A set of constraints that specifies the limits of the runtime's memory use.
   * You must set the heap size before initializing the VM - the size cannot be
   * adjusted after the VM is initialized.
   *
   * If you are using threads then you should hold the V8::Locker lock while
   * setting the stack limit and you must set a non-default stack limit separately
   * for each thread.
   *
   * The arguments for set_max_semi_space_size, set_max_old_space_size,
   * set_max_executable_size, set_code_range_size specify limits in MB.
   *
   * The argument for set_max_semi_space_size_in_kb is in KB.
   */
  class V8_EXPORT ResourceConstraints {
   public:
    /**
     * Configures the constraints with reasonable default values based on the
     * provided heap size limit. The heap size includes both the young and
     * the old generation.
     *
     * \param maximum_heap_size_in_bytes The hard limit for the heap size.
     *    When the heap size approaches this limit, V8 will perform series of
     *    garbage collections and invoke the NearHeapLimitCallback.
     *    If the garbage collections do not help and the callback does not
     * increase the limit, then V8 will crash with V8::FatalProcessOutOfMemory.
     */
    void ConfigureDefaultsFromHeapSize(size_t initial_heap_size_in_bytes,
                                       size_t maximum_heap_size_in_bytes);
  
    /**
     * Configures the constraints with reasonable default values based on the
     * capabilities of the current device the VM is running on.
     *
     * \param physical_memory The total amount of physical memory on the current
     *   device, in bytes.
     * \param virtual_memory_limit The amount of virtual memory on the current
     *   device, in bytes, or zero, if there is no limit.
     */
    void ConfigureDefaults(uint64_t physical_memory,
                           uint64_t virtual_memory_limit);
  
    /**
     * The address beyond which the VM's stack may not grow.
     */
    uint32_t* stack_limit() const { return stack_limit_; }
    void set_stack_limit(uint32_t* value) { stack_limit_ = value; }
  
    /**
     * The amount of virtual memory reserved for generated code. This is relevant
     * for 64-bit architectures that rely on code range for calls in code.
     */
    size_t code_range_size_in_bytes() const { return code_range_size_; }
    void set_code_range_size_in_bytes(size_t limit) { code_range_size_ = limit; }
  
    /**
     * The maximum size of the old generation.
     * When the old generation approaches this limit, V8 will perform series of
     * garbage collections and invoke the NearHeapLimitCallback.
     * If the garbage collections do not help and the callback does not
     * increase the limit, then V8 will crash with V8::FatalProcessOutOfMemory.
     */
    size_t max_old_generation_size_in_bytes() const {
      return max_old_generation_size_;
    }
    void set_max_old_generation_size_in_bytes(size_t limit) {
      max_old_generation_size_ = limit;
    }
  
    /**
     * The maximum size of the young generation, which consists of two semi-spaces
     * and a large object space. This affects frequency of Scavenge garbage
     * collections and should be typically much smaller that the old generation.
     */
    size_t max_young_generation_size_in_bytes() const {
      return max_young_generation_size_;
    }
    void set_max_young_generation_size_in_bytes(size_t limit) {
      max_young_generation_size_ = limit;
    }
  
    size_t initial_old_generation_size_in_bytes() const {
      return initial_old_generation_size_;
    }
    void set_initial_old_generation_size_in_bytes(size_t initial_size) {
      initial_old_generation_size_ = initial_size;
    }
  
    size_t initial_young_generation_size_in_bytes() const {
      return initial_young_generation_size_;
    }
    void set_initial_young_generation_size_in_bytes(size_t initial_size) {
      initial_young_generation_size_ = initial_size;
    }
  
    /**
     * Deprecated functions. Do not use in new code.
     */
    V8_DEPRECATE_SOON("Use code_range_size_in_bytes.",
                      size_t code_range_size() const) {
      return code_range_size_ / kMB;
    }
    V8_DEPRECATE_SOON("Use set_code_range_size_in_bytes.",
                      void set_code_range_size(size_t limit_in_mb)) {
      code_range_size_ = limit_in_mb * kMB;
    }
    V8_DEPRECATE_SOON("Use max_young_generation_size_in_bytes.",
                      size_t max_semi_space_size_in_kb() const);
    V8_DEPRECATE_SOON("Use set_max_young_generation_size_in_bytes.",
                      void set_max_semi_space_size_in_kb(size_t limit_in_kb));
    V8_DEPRECATE_SOON("Use max_old_generation_size_in_bytes.",
                      size_t max_old_space_size() const) {
      return max_old_generation_size_ / kMB;
    }
    V8_DEPRECATE_SOON("Use set_max_old_generation_size_in_bytes.",
                      void set_max_old_space_size(size_t limit_in_mb)) {
      max_old_generation_size_ = limit_in_mb * kMB;
    }
    V8_DEPRECATE_SOON("Zone does not pool memory any more.",
                      size_t max_zone_pool_size() const) {
      return max_zone_pool_size_;
    }
    V8_DEPRECATE_SOON("Zone does not pool memory any more.",
                      void set_max_zone_pool_size(size_t bytes)) {
      max_zone_pool_size_ = bytes;
    }
  
   private:
    static constexpr size_t kMB = 1048576u;
    size_t code_range_size_ = 0;
    size_t max_old_generation_size_ = 0;
    size_t max_young_generation_size_ = 0;
    size_t max_zone_pool_size_ = 0;
    size_t initial_old_generation_size_ = 0;
    size_t initial_young_generation_size_ = 0;
    uint32_t* stack_limit_ = nullptr;
  };
  
  
  // --- Exceptions ---
  
  
  typedef void (*FatalErrorCallback)(const char* location, const char* message);
  
  typedef void (*OOMErrorCallback)(const char* location, bool is_heap_oom);
  
  typedef void (*DcheckErrorCallback)(const char* file, int line,
                                      const char* message);
  
  typedef void (*MessageCallback)(Local<Message> message, Local<Value> data);
  
  // --- Tracing ---
  
  typedef void (*LogEventCallback)(const char* name, int event);
  
  /**
   * Create new error objects by calling the corresponding error object
   * constructor with the message.
   */
  class V8_EXPORT Exception {
   public:
    static Local<Value> RangeError(Local<String> message);
    static Local<Value> ReferenceError(Local<String> message);
    static Local<Value> SyntaxError(Local<String> message);
    static Local<Value> TypeError(Local<String> message);
    static Local<Value> Error(Local<String> message);
  
    /**
     * Creates an error message for the given exception.
     * Will try to reconstruct the original stack trace from the exception value,
     * or capture the current stack trace if not available.
     */
    static Local<Message> CreateMessage(Isolate* isolate, Local<Value> exception);
  
    /**
     * Returns the original stack trace that was captured at the creation time
     * of a given exception, or an empty handle if not available.
     */
    static Local<StackTrace> GetStackTrace(Local<Value> exception);
  };
  
  
  // --- Counters Callbacks ---
  
  typedef int* (*CounterLookupCallback)(const char* name);
  
  typedef void* (*CreateHistogramCallback)(const char* name,
                                           int min,
                                           int max,
                                           size_t buckets);
  
  typedef void (*AddHistogramSampleCallback)(void* histogram, int sample);
  
  // --- Enter/Leave Script Callback ---
  typedef void (*BeforeCallEnteredCallback)(Isolate*);
  typedef void (*CallCompletedCallback)(Isolate*);
  
  /**
   * HostImportModuleDynamicallyCallback is called when we require the
   * embedder to load a module. This is used as part of the dynamic
   * import syntax.
   *
   * The referrer contains metadata about the script/module that calls
   * import.
   *
   * The specifier is the name of the module that should be imported.
   *
   * The embedder must compile, instantiate, evaluate the Module, and
   * obtain it's namespace object.
   *
   * The Promise returned from this function is forwarded to userland
   * JavaScript. The embedder must resolve this promise with the module
   * namespace object. In case of an exception, the embedder must reject
   * this promise with the exception. If the promise creation itself
   * fails (e.g. due to stack overflow), the embedder must propagate
   * that exception by returning an empty MaybeLocal.
   */
  typedef MaybeLocal<Promise> (*HostImportModuleDynamicallyCallback)(
      Local<Context> context, Local<ScriptOrModule> referrer,
      Local<String> specifier);
  
  /**
   * HostInitializeImportMetaObjectCallback is called the first time import.meta
   * is accessed for a module. Subsequent access will reuse the same value.
   *
   * The method combines two implementation-defined abstract operations into one:
   * HostGetImportMetaProperties and HostFinalizeImportMeta.
   *
   * The embedder should use v8::Object::CreateDataProperty to add properties on
   * the meta object.
   */
  typedef void (*HostInitializeImportMetaObjectCallback)(Local<Context> context,
                                                         Local<Module> module,
                                                         Local<Object> meta);
  
  /**
   * PrepareStackTraceCallback is called when the stack property of an error is
   * first accessed. The return value will be used as the stack value. If this
   * callback is registed, the |Error.prepareStackTrace| API will be disabled.
   * |sites| is an array of call sites, specified in
   * https://v8.dev/docs/stack-trace-api
   */
  typedef MaybeLocal<Value> (*PrepareStackTraceCallback)(Local<Context> context,
                                                         Local<Value> error,
                                                         Local<Array> sites);
  
  /**
   * PromiseHook with type kInit is called when a new promise is
   * created. When a new promise is created as part of the chain in the
   * case of Promise.then or in the intermediate promises created by
   * Promise.{race, all}/AsyncFunctionAwait, we pass the parent promise
   * otherwise we pass undefined.
   *
   * PromiseHook with type kResolve is called at the beginning of
   * resolve or reject function defined by CreateResolvingFunctions.
   *
   * PromiseHook with type kBefore is called at the beginning of the
   * PromiseReactionJob.
   *
   * PromiseHook with type kAfter is called right at the end of the
   * PromiseReactionJob.
   */
  enum class PromiseHookType { kInit, kResolve, kBefore, kAfter };
  
  typedef void (*PromiseHook)(PromiseHookType type, Local<Promise> promise,
                              Local<Value> parent);
  
  // --- Promise Reject Callback ---
  enum PromiseRejectEvent {
    kPromiseRejectWithNoHandler = 0,
    kPromiseHandlerAddedAfterReject = 1,
    kPromiseRejectAfterResolved = 2,
    kPromiseResolveAfterResolved = 3,
  };
  
  class PromiseRejectMessage {
   public:
    PromiseRejectMessage(Local<Promise> promise, PromiseRejectEvent event,
                         Local<Value> value)
        : promise_(promise), event_(event), value_(value) {}
  
    V8_INLINE Local<Promise> GetPromise() const { return promise_; }
    V8_INLINE PromiseRejectEvent GetEvent() const { return event_; }
    V8_INLINE Local<Value> GetValue() const { return value_; }
  
   private:
    Local<Promise> promise_;
    PromiseRejectEvent event_;
    Local<Value> value_;
  };
  
  typedef void (*PromiseRejectCallback)(PromiseRejectMessage message);
  
  // --- Microtasks Callbacks ---
  V8_DEPRECATE_SOON("Use *WithData version.",
                    typedef void (*MicrotasksCompletedCallback)(Isolate*));
  typedef void (*MicrotasksCompletedCallbackWithData)(Isolate*, void*);
  typedef void (*MicrotaskCallback)(void* data);
  
  
  /**
   * Policy for running microtasks:
   *   - explicit: microtasks are invoked with Isolate::RunMicrotasks() method;
   *   - scoped: microtasks invocation is controlled by MicrotasksScope objects;
   *   - auto: microtasks are invoked when the script call depth decrements
   *           to zero.
   */
  enum class MicrotasksPolicy { kExplicit, kScoped, kAuto };
  
  /**
   * Represents the microtask queue, where microtasks are stored and processed.
   * https://html.spec.whatwg.org/multipage/webappapis.html#microtask-queue
   * https://html.spec.whatwg.org/multipage/webappapis.html#enqueuejob(queuename,-job,-arguments)
   * https://html.spec.whatwg.org/multipage/webappapis.html#perform-a-microtask-checkpoint
   *
   * A MicrotaskQueue instance may be associated to multiple Contexts by passing
   * it to Context::New(), and they can be detached by Context::DetachGlobal().
   * The embedder must keep the MicrotaskQueue instance alive until all associated
   * Contexts are gone or detached.
   *
   * Use the same instance of MicrotaskQueue for all Contexts that may access each
   * other synchronously. E.g. for Web embedding, use the same instance for all
   * origins that share the same URL scheme and eTLD+1.
   */
  class V8_EXPORT MicrotaskQueue {
   public:
    /**
     * Creates an empty MicrotaskQueue instance.
     */
    static std::unique_ptr<MicrotaskQueue> New(
        Isolate* isolate, MicrotasksPolicy policy = MicrotasksPolicy::kAuto);
  
    virtual ~MicrotaskQueue() = default;
  
    /**
     * Enqueues the callback to the queue.
     */
    virtual void EnqueueMicrotask(Isolate* isolate,
                                  Local<Function> microtask) = 0;
  
    /**
     * Enqueues the callback to the queue.
     */
    virtual void EnqueueMicrotask(v8::Isolate* isolate,
                                  MicrotaskCallback callback,
                                  void* data = nullptr) = 0;
  
    /**
     * Adds a callback to notify the embedder after microtasks were run. The
     * callback is triggered by explicit RunMicrotasks call or automatic
     * microtasks execution (see Isolate::SetMicrotasksPolicy).
     *
     * Callback will trigger even if microtasks were attempted to run,
     * but the microtasks queue was empty and no single microtask was actually
     * executed.
     *
     * Executing scripts inside the callback will not re-trigger microtasks and
     * the callback.
     */
    virtual void AddMicrotasksCompletedCallback(
        MicrotasksCompletedCallbackWithData callback, void* data = nullptr) = 0;
  
    /**
     * Removes callback that was installed by AddMicrotasksCompletedCallback.
     */
    virtual void RemoveMicrotasksCompletedCallback(
        MicrotasksCompletedCallbackWithData callback, void* data = nullptr) = 0;
  
    /**
     * Runs microtasks if no microtask is running on this MicrotaskQueue instance.
     */
    virtual void PerformCheckpoint(Isolate* isolate) = 0;
  
    /**
     * Returns true if a microtask is running on this MicrotaskQueue instance.
     */
    virtual bool IsRunningMicrotasks() const = 0;
  
    /**
     * Returns the current depth of nested MicrotasksScope that has
     * kRunMicrotasks.
     */
    virtual int GetMicrotasksScopeDepth() const = 0;
  
    MicrotaskQueue(const MicrotaskQueue&) = delete;
    MicrotaskQueue& operator=(const MicrotaskQueue&) = delete;
  
   private:
    friend class internal::MicrotaskQueue;
    MicrotaskQueue() = default;
  };
  
  /**
   * This scope is used to control microtasks when kScopeMicrotasksInvocation
   * is used on Isolate. In this mode every non-primitive call to V8 should be
   * done inside some MicrotasksScope.
   * Microtasks are executed when topmost MicrotasksScope marked as kRunMicrotasks
   * exits.
   * kDoNotRunMicrotasks should be used to annotate calls not intended to trigger
   * microtasks.
   */
  class V8_EXPORT MicrotasksScope {
   public:
    enum Type { kRunMicrotasks, kDoNotRunMicrotasks };
  
    MicrotasksScope(Isolate* isolate, Type type);
    MicrotasksScope(Isolate* isolate, MicrotaskQueue* microtask_queue, Type type);
    ~MicrotasksScope();
  
    /**
     * Runs microtasks if no kRunMicrotasks scope is currently active.
     */
    static void PerformCheckpoint(Isolate* isolate);
  
    /**
     * Returns current depth of nested kRunMicrotasks scopes.
     */
    static int GetCurrentDepth(Isolate* isolate);
  
    /**
     * Returns true while microtasks are being executed.
     */
    static bool IsRunningMicrotasks(Isolate* isolate);
  
    // Prevent copying.
    MicrotasksScope(const MicrotasksScope&) = delete;
    MicrotasksScope& operator=(const MicrotasksScope&) = delete;
  
   private:
    internal::Isolate* const isolate_;
    internal::MicrotaskQueue* const microtask_queue_;
    bool run_;
  };
  
  
  // --- Failed Access Check Callback ---
  typedef void (*FailedAccessCheckCallback)(Local<Object> target,
                                            AccessType type,
                                            Local<Value> data);
  
  // --- AllowCodeGenerationFromStrings callbacks ---
  
  /**
   * Callback to check if code generation from strings is allowed. See
   * Context::AllowCodeGenerationFromStrings.
   */
  typedef bool (*AllowCodeGenerationFromStringsCallback)(Local<Context> context,
                                                         Local<String> source);
  
  // --- WebAssembly compilation callbacks ---
  typedef bool (*ExtensionCallback)(const FunctionCallbackInfo<Value>&);
  
  typedef bool (*AllowWasmCodeGenerationCallback)(Local<Context> context,
                                                  Local<String> source);
  
  // --- Callback for APIs defined on v8-supported objects, but implemented
  // by the embedder. Example: WebAssembly.{compile|instantiate}Streaming ---
  typedef void (*ApiImplementationCallback)(const FunctionCallbackInfo<Value>&);
  
  // --- Callback for WebAssembly.compileStreaming ---
  typedef void (*WasmStreamingCallback)(const FunctionCallbackInfo<Value>&);
  
  // --- Callback for checking if WebAssembly threads are enabled ---
  typedef bool (*WasmThreadsEnabledCallback)(Local<Context> context);
  
  // --- Garbage Collection Callbacks ---
  
  /**
   * Applications can register callback functions which will be called before and
   * after certain garbage collection operations.  Allocations are not allowed in
   * the callback functions, you therefore cannot manipulate objects (set or
   * delete properties for example) since it is possible such operations will
   * result in the allocation of objects.
   */
  enum GCType {
    kGCTypeScavenge = 1 << 0,
    kGCTypeMarkSweepCompact = 1 << 1,
    kGCTypeIncrementalMarking = 1 << 2,
    kGCTypeProcessWeakCallbacks = 1 << 3,
    kGCTypeAll = kGCTypeScavenge | kGCTypeMarkSweepCompact |
                 kGCTypeIncrementalMarking | kGCTypeProcessWeakCallbacks
  };
  
  /**
   * GCCallbackFlags is used to notify additional information about the GC
   * callback.
   *   - kGCCallbackFlagConstructRetainedObjectInfos: The GC callback is for
   *     constructing retained object infos.
   *   - kGCCallbackFlagForced: The GC callback is for a forced GC for testing.
   *   - kGCCallbackFlagSynchronousPhantomCallbackProcessing: The GC callback
   *     is called synchronously without getting posted to an idle task.
   *   - kGCCallbackFlagCollectAllAvailableGarbage: The GC callback is called
   *     in a phase where V8 is trying to collect all available garbage
   *     (e.g., handling a low memory notification).
   *   - kGCCallbackScheduleIdleGarbageCollection: The GC callback is called to
   *     trigger an idle garbage collection.
   */
  enum GCCallbackFlags {
    kNoGCCallbackFlags = 0,
    kGCCallbackFlagConstructRetainedObjectInfos = 1 << 1,
    kGCCallbackFlagForced = 1 << 2,
    kGCCallbackFlagSynchronousPhantomCallbackProcessing = 1 << 3,
    kGCCallbackFlagCollectAllAvailableGarbage = 1 << 4,
    kGCCallbackFlagCollectAllExternalMemory = 1 << 5,
    kGCCallbackScheduleIdleGarbageCollection = 1 << 6,
  };
  
  typedef void (*GCCallback)(GCType type, GCCallbackFlags flags);
  
  typedef void (*InterruptCallback)(Isolate* isolate, void* data);
  
  /**
   * This callback is invoked when the heap size is close to the heap limit and
   * V8 is likely to abort with out-of-memory error.
   * The callback can extend the heap limit by returning a value that is greater
   * than the current_heap_limit. The initial heap limit is the limit that was
   * set after heap setup.
   */
  typedef size_t (*NearHeapLimitCallback)(void* data, size_t current_heap_limit,
                                          size_t initial_heap_limit);
  
  /**
   * Collection of V8 heap information.
   *
   * Instances of this class can be passed to v8::V8::HeapStatistics to
   * get heap statistics from V8.
   */
  class V8_EXPORT HeapStatistics {
   public:
    HeapStatistics();
    size_t total_heap_size() { return total_heap_size_; }
    size_t total_heap_size_executable() { return total_heap_size_executable_; }
    size_t total_physical_size() { return total_physical_size_; }
    size_t total_available_size() { return total_available_size_; }
    size_t used_heap_size() { return used_heap_size_; }
    size_t heap_size_limit() { return heap_size_limit_; }
    size_t malloced_memory() { return malloced_memory_; }
    size_t external_memory() { return external_memory_; }
    size_t peak_malloced_memory() { return peak_malloced_memory_; }
    size_t number_of_native_contexts() { return number_of_native_contexts_; }
    size_t number_of_detached_contexts() { return number_of_detached_contexts_; }
  
    /**
     * Returns a 0/1 boolean, which signifies whether the V8 overwrite heap
     * garbage with a bit pattern.
     */
    size_t does_zap_garbage() { return does_zap_garbage_; }
  
   private:
    size_t total_heap_size_;
    size_t total_heap_size_executable_;
    size_t total_physical_size_;
    size_t total_available_size_;
    size_t used_heap_size_;
    size_t heap_size_limit_;
    size_t malloced_memory_;
    size_t external_memory_;
    size_t peak_malloced_memory_;
    bool does_zap_garbage_;
    size_t number_of_native_contexts_;
    size_t number_of_detached_contexts_;
  
    friend class V8;
    friend class Isolate;
  };
  
  
  class V8_EXPORT HeapSpaceStatistics {
   public:
    HeapSpaceStatistics();
    const char* space_name() { return space_name_; }
    size_t space_size() { return space_size_; }
    size_t space_used_size() { return space_used_size_; }
    size_t space_available_size() { return space_available_size_; }
    size_t physical_space_size() { return physical_space_size_; }
  
   private:
    const char* space_name_;
    size_t space_size_;
    size_t space_used_size_;
    size_t space_available_size_;
    size_t physical_space_size_;
  
    friend class Isolate;
  };
  
  
  class V8_EXPORT HeapObjectStatistics {
   public:
    HeapObjectStatistics();
    const char* object_type() { return object_type_; }
    const char* object_sub_type() { return object_sub_type_; }
    size_t object_count() { return object_count_; }
    size_t object_size() { return object_size_; }
  
   private:
    const char* object_type_;
    const char* object_sub_type_;
    size_t object_count_;
    size_t object_size_;
  
    friend class Isolate;
  };
  
  class V8_EXPORT HeapCodeStatistics {
   public:
    HeapCodeStatistics();
    size_t code_and_metadata_size() { return code_and_metadata_size_; }
    size_t bytecode_and_metadata_size() { return bytecode_and_metadata_size_; }
    size_t external_script_source_size() { return external_script_source_size_; }
  
   private:
    size_t code_and_metadata_size_;
    size_t bytecode_and_metadata_size_;
    size_t external_script_source_size_;
  
    friend class Isolate;
  };
  
  /**
   * A JIT code event is issued each time code is added, moved or removed.
   *
   * \note removal events are not currently issued.
   */
  struct JitCodeEvent {
    enum EventType {
      CODE_ADDED,
      CODE_MOVED,
      CODE_REMOVED,
      CODE_ADD_LINE_POS_INFO,
      CODE_START_LINE_INFO_RECORDING,
      CODE_END_LINE_INFO_RECORDING
    };
    // Definition of the code position type. The "POSITION" type means the place
    // in the source code which are of interest when making stack traces to
    // pin-point the source location of a stack frame as close as possible.
    // The "STATEMENT_POSITION" means the place at the beginning of each
    // statement, and is used to indicate possible break locations.
    enum PositionType { POSITION, STATEMENT_POSITION };
  
    // There are two different kinds of JitCodeEvents, one for JIT code generated
    // by the optimizing compiler, and one for byte code generated for the
    // interpreter.  For JIT_CODE events, the |code_start| member of the event
    // points to the beginning of jitted assembly code, while for BYTE_CODE
    // events, |code_start| points to the first bytecode of the interpreted
    // function.
    enum CodeType { BYTE_CODE, JIT_CODE };
  
    // Type of event.
    EventType type;
    CodeType code_type;
    // Start of the instructions.
    void* code_start;
    // Size of the instructions.
    size_t code_len;
    // Script info for CODE_ADDED event.
    Local<UnboundScript> script;
    // User-defined data for *_LINE_INFO_* event. It's used to hold the source
    // code line information which is returned from the
    // CODE_START_LINE_INFO_RECORDING event. And it's passed to subsequent
    // CODE_ADD_LINE_POS_INFO and CODE_END_LINE_INFO_RECORDING events.
    void* user_data;
  
    struct name_t {
      // Name of the object associated with the code, note that the string is not
      // zero-terminated.
      const char* str;
      // Number of chars in str.
      size_t len;
    };
  
    struct line_info_t {
      // PC offset
      size_t offset;
      // Code position
      size_t pos;
      // The position type.
      PositionType position_type;
    };
  
    union {
      // Only valid for CODE_ADDED.
      struct name_t name;
  
      // Only valid for CODE_ADD_LINE_POS_INFO
      struct line_info_t line_info;
  
      // New location of instructions. Only valid for CODE_MOVED.
      void* new_code_start;
    };
  
    Isolate* isolate;
  };
  
  /**
   * Option flags passed to the SetRAILMode function.
   * See documentation https://developers.google.com/web/tools/chrome-devtools/
   * profile/evaluate-performance/rail
   */
  enum RAILMode : unsigned {
    // Response performance mode: In this mode very low virtual machine latency
    // is provided. V8 will try to avoid JavaScript execution interruptions.
    // Throughput may be throttled.
    PERFORMANCE_RESPONSE,
    // Animation performance mode: In this mode low virtual machine latency is
    // provided. V8 will try to avoid as many JavaScript execution interruptions
    // as possible. Throughput may be throttled. This is the default mode.
    PERFORMANCE_ANIMATION,
    // Idle performance mode: The embedder is idle. V8 can complete deferred work
    // in this mode.
    PERFORMANCE_IDLE,
    // Load performance mode: In this mode high throughput is provided. V8 may
    // turn off latency optimizations.
    PERFORMANCE_LOAD
  };
  
  /**
   * Option flags passed to the SetJitCodeEventHandler function.
   */
  enum JitCodeEventOptions {
    kJitCodeEventDefault = 0,
    // Generate callbacks for already existent code.
    kJitCodeEventEnumExisting = 1
  };
  
  
  /**
   * Callback function passed to SetJitCodeEventHandler.
   *
   * \param event code add, move or removal event.
   */
  typedef void (*JitCodeEventHandler)(const JitCodeEvent* event);
  
  /**
   * Callback function passed to SetUnhandledExceptionCallback.
   */
  #if defined(V8_OS_WIN)
  typedef int (*UnhandledExceptionCallback)(
      _EXCEPTION_POINTERS* exception_pointers);
  #endif
  
  /**
   * Interface for iterating through all external resources in the heap.
   */
  class V8_EXPORT ExternalResourceVisitor {  // NOLINT
   public:
    virtual ~ExternalResourceVisitor() = default;
    virtual void VisitExternalString(Local<String> string) {}
  };
  
  
  /**
   * Interface for iterating through all the persistent handles in the heap.
   */
  class V8_EXPORT PersistentHandleVisitor {  // NOLINT
   public:
    virtual ~PersistentHandleVisitor() = default;
    virtual void VisitPersistentHandle(Persistent<Value>* value,
                                       uint16_t class_id) {}
  };
  
  /**
   * Memory pressure level for the MemoryPressureNotification.
   * kNone hints V8 that there is no memory pressure.
   * kModerate hints V8 to speed up incremental garbage collection at the cost of
   * of higher latency due to garbage collection pauses.
   * kCritical hints V8 to free memory as soon as possible. Garbage collection
   * pauses at this level will be large.
   */
  enum class MemoryPressureLevel { kNone, kModerate, kCritical };
  
  /**
   * Interface for tracing through the embedder heap. During a V8 garbage
   * collection, V8 collects hidden fields of all potential wrappers, and at the
   * end of its marking phase iterates the collection and asks the embedder to
   * trace through its heap and use reporter to report each JavaScript object
   * reachable from any of the given wrappers.
   */
  class V8_EXPORT EmbedderHeapTracer {
   public:
    enum TraceFlags : uint64_t {
      kNoFlags = 0,
      kReduceMemory = 1 << 0,
    };
  
    // Indicator for the stack state of the embedder.
    enum EmbedderStackState {
      kUnknown,
      kNonEmpty,
      kEmpty,
    };
  
    /**
     * Interface for iterating through TracedGlobal handles.
     */
    class V8_EXPORT TracedGlobalHandleVisitor {
     public:
      virtual ~TracedGlobalHandleVisitor() = default;
      virtual void VisitTracedGlobalHandle(const TracedGlobal<Value>& value) = 0;
    };
  
    /**
     * Summary of a garbage collection cycle. See |TraceEpilogue| on how the
     * summary is reported.
     */
    struct TraceSummary {
      /**
       * Time spent managing the retained memory in milliseconds. This can e.g.
       * include the time tracing through objects in the embedder.
       */
      double time = 0.0;
  
      /**
       * Memory retained by the embedder through the |EmbedderHeapTracer|
       * mechanism in bytes.
       */
      size_t allocated_size = 0;
    };
  
    virtual ~EmbedderHeapTracer() = default;
  
    /**
     * Iterates all TracedGlobal handles created for the v8::Isolate the tracer is
     * attached to.
     */
    void IterateTracedGlobalHandles(TracedGlobalHandleVisitor* visitor);
  
    /**
     * Called by v8 to register internal fields of found wrappers.
     *
     * The embedder is expected to store them somewhere and trace reachable
     * wrappers from them when called through |AdvanceTracing|.
     */
    virtual void RegisterV8References(
        const std::vector<std::pair<void*, void*> >& embedder_fields) = 0;
  
    void RegisterEmbedderReference(const TracedGlobal<v8::Value>& ref);
  
    /**
     * Called at the beginning of a GC cycle.
     */
    V8_DEPRECATE_SOON("Use version with flags.", virtual void TracePrologue()) {}
    virtual void TracePrologue(TraceFlags flags);
  
    /**
     * Called to advance tracing in the embedder.
     *
     * The embedder is expected to trace its heap starting from wrappers reported
     * by RegisterV8References method, and report back all reachable wrappers.
     * Furthermore, the embedder is expected to stop tracing by the given
     * deadline. A deadline of infinity means that tracing should be finished.
     *
     * Returns |true| if tracing is done, and false otherwise.
     */
    virtual bool AdvanceTracing(double deadline_in_ms) = 0;
  
    /*
     * Returns true if there no more tracing work to be done (see AdvanceTracing)
     * and false otherwise.
     */
    virtual bool IsTracingDone() = 0;
  
    /**
     * Called at the end of a GC cycle.
     *
     * Note that allocation is *not* allowed within |TraceEpilogue|. Can be
     * overriden to fill a |TraceSummary| that is used by V8 to schedule future
     * garbage collections.
     */
    virtual void TraceEpilogue() {}
    virtual void TraceEpilogue(TraceSummary* trace_summary) { TraceEpilogue(); }
  
    /**
     * Called upon entering the final marking pause. No more incremental marking
     * steps will follow this call.
     */
    virtual void EnterFinalPause(EmbedderStackState stack_state) = 0;
  
    /*
     * Called by the embedder to request immediate finalization of the currently
     * running tracing phase that has been started with TracePrologue and not
     * yet finished with TraceEpilogue.
     *
     * Will be a noop when currently not in tracing.
     *
     * This is an experimental feature.
     */
    void FinalizeTracing();
  
    /**
     * Returns true if the TracedGlobal handle should be considered as root for
     * the currently running non-tracing garbage collection and false otherwise.
     *
     * Default implementation will keep all TracedGlobal references as roots.
     */
    virtual bool IsRootForNonTracingGC(
        const v8::TracedGlobal<v8::Value>& handle) {
      return true;
    }
  
    /*
     * Called by the embedder to immediately perform a full garbage collection.
     *
     * Should only be used in testing code.
     */
    void GarbageCollectionForTesting(EmbedderStackState stack_state);
  
    /*
     * Called by the embedder to signal newly allocated or freed memory. Not bound
     * to tracing phases. Embedders should trade off when increments are reported
     * as V8 may consult global heuristics on whether to trigger garbage
     * collection on this change.
     */
    void IncreaseAllocatedSize(size_t bytes);
    void DecreaseAllocatedSize(size_t bytes);
  
    /*
     * Returns the v8::Isolate this tracer is attached too and |nullptr| if it
     * is not attached to any v8::Isolate.
     */
    v8::Isolate* isolate() const { return isolate_; }
  
   protected:
    v8::Isolate* isolate_ = nullptr;
  
    friend class internal::LocalEmbedderHeapTracer;
  };
  
  /**
   * Callback and supporting data used in SnapshotCreator to implement embedder
   * logic to serialize internal fields.
   * Internal fields that directly reference V8 objects are serialized without
   * calling this callback. Internal fields that contain aligned pointers are
   * serialized by this callback if it returns non-zero result. Otherwise it is
   * serialized verbatim.
   */
  struct SerializeInternalFieldsCallback {
    typedef StartupData (*CallbackFunction)(Local<Object> holder, int index,
                                            void* data);
    SerializeInternalFieldsCallback(CallbackFunction function = nullptr,
                                    void* data_arg = nullptr)
        : callback(function), data(data_arg) {}
    CallbackFunction callback;
    void* data;
  };
  // Note that these fields are called "internal fields" in the API and called
  // "embedder fields" within V8.
  typedef SerializeInternalFieldsCallback SerializeEmbedderFieldsCallback;
  
  /**
   * Callback and supporting data used to implement embedder logic to deserialize
   * internal fields.
   */
  struct DeserializeInternalFieldsCallback {
    typedef void (*CallbackFunction)(Local<Object> holder, int index,
                                     StartupData payload, void* data);
    DeserializeInternalFieldsCallback(CallbackFunction function = nullptr,
                                      void* data_arg = nullptr)
        : callback(function), data(data_arg) {}
    void (*callback)(Local<Object> holder, int index, StartupData payload,
                     void* data);
    void* data;
  };
  typedef DeserializeInternalFieldsCallback DeserializeEmbedderFieldsCallback;
  
  /**
   * Isolate represents an isolated instance of the V8 engine.  V8 isolates have
   * completely separate states.  Objects from one isolate must not be used in
   * other isolates.  The embedder can create multiple isolates and use them in
   * parallel in multiple threads.  An isolate can be entered by at most one
   * thread at any given time.  The Locker/Unlocker API must be used to
   * synchronize.
   */
  class V8_EXPORT Isolate {
   public:
    /**
     * Initial configuration parameters for a new Isolate.
     */
    struct CreateParams {
      CreateParams()
          : code_event_handler(nullptr),
            snapshot_blob(nullptr),
            counter_lookup_callback(nullptr),
            create_histogram_callback(nullptr),
            add_histogram_sample_callback(nullptr),
            array_buffer_allocator(nullptr),
            external_references(nullptr),
            allow_atomics_wait(true),
            only_terminate_in_safe_scope(false) {}
  
      /**
       * Allows the host application to provide the address of a function that is
       * notified each time code is added, moved or removed.
       */
      JitCodeEventHandler code_event_handler;
  
      /**
       * ResourceConstraints to use for the new Isolate.
       */
      ResourceConstraints constraints;
  
      /**
       * Explicitly specify a startup snapshot blob. The embedder owns the blob.
       */
      StartupData* snapshot_blob;
  
  
      /**
       * Enables the host application to provide a mechanism for recording
       * statistics counters.
       */
      CounterLookupCallback counter_lookup_callback;
  
      /**
       * Enables the host application to provide a mechanism for recording
       * histograms. The CreateHistogram function returns a
       * histogram which will later be passed to the AddHistogramSample
       * function.
       */
      CreateHistogramCallback create_histogram_callback;
      AddHistogramSampleCallback add_histogram_sample_callback;
  
      /**
       * The ArrayBuffer::Allocator to use for allocating and freeing the backing
       * store of ArrayBuffers.
       */
      ArrayBuffer::Allocator* array_buffer_allocator;
  
      /**
       * Specifies an optional nullptr-terminated array of raw addresses in the
       * embedder that V8 can match against during serialization and use for
       * deserialization. This array and its content must stay valid for the
       * entire lifetime of the isolate.
       */
      const intptr_t* external_references;
  
      /**
       * Whether calling Atomics.wait (a function that may block) is allowed in
       * this isolate. This can also be configured via SetAllowAtomicsWait.
       */
      bool allow_atomics_wait;
  
      /**
       * Termination is postponed when there is no active SafeForTerminationScope.
       */
      bool only_terminate_in_safe_scope;
    };
  
  
    /**
     * Stack-allocated class which sets the isolate for all operations
     * executed within a local scope.
     */
    class V8_EXPORT Scope {
     public:
      explicit Scope(Isolate* isolate) : isolate_(isolate) {
        isolate->Enter();
      }
  
      ~Scope() { isolate_->Exit(); }
  
      // Prevent copying of Scope objects.
      Scope(const Scope&) = delete;
      Scope& operator=(const Scope&) = delete;
  
     private:
      Isolate* const isolate_;
    };
  
  
    /**
     * Assert that no Javascript code is invoked.
     */
    class V8_EXPORT DisallowJavascriptExecutionScope {
     public:
      enum OnFailure { CRASH_ON_FAILURE, THROW_ON_FAILURE, DUMP_ON_FAILURE };
  
      DisallowJavascriptExecutionScope(Isolate* isolate, OnFailure on_failure);
      ~DisallowJavascriptExecutionScope();
  
      // Prevent copying of Scope objects.
      DisallowJavascriptExecutionScope(const DisallowJavascriptExecutionScope&) =
          delete;
      DisallowJavascriptExecutionScope& operator=(
          const DisallowJavascriptExecutionScope&) = delete;
  
     private:
      OnFailure on_failure_;
      void* internal_;
    };
  
  
    /**
     * Introduce exception to DisallowJavascriptExecutionScope.
     */
    class V8_EXPORT AllowJavascriptExecutionScope {
     public:
      explicit AllowJavascriptExecutionScope(Isolate* isolate);
      ~AllowJavascriptExecutionScope();
  
      // Prevent copying of Scope objects.
      AllowJavascriptExecutionScope(const AllowJavascriptExecutionScope&) =
          delete;
      AllowJavascriptExecutionScope& operator=(
          const AllowJavascriptExecutionScope&) = delete;
  
     private:
      void* internal_throws_;
      void* internal_assert_;
      void* internal_dump_;
    };
  
    /**
     * Do not run microtasks while this scope is active, even if microtasks are
     * automatically executed otherwise.
     */
    class V8_EXPORT SuppressMicrotaskExecutionScope {
     public:
      explicit SuppressMicrotaskExecutionScope(Isolate* isolate);
      explicit SuppressMicrotaskExecutionScope(MicrotaskQueue* microtask_queue);
      ~SuppressMicrotaskExecutionScope();
  
      // Prevent copying of Scope objects.
      SuppressMicrotaskExecutionScope(const SuppressMicrotaskExecutionScope&) =
          delete;
      SuppressMicrotaskExecutionScope& operator=(
          const SuppressMicrotaskExecutionScope&) = delete;
  
     private:
      internal::Isolate* const isolate_;
      internal::MicrotaskQueue* const microtask_queue_;
    };
  
    /**
     * This scope allows terminations inside direct V8 API calls and forbid them
     * inside any recursice API calls without explicit SafeForTerminationScope.
     */
    class V8_EXPORT SafeForTerminationScope {
     public:
      explicit SafeForTerminationScope(v8::Isolate* isolate);
      ~SafeForTerminationScope();
  
      // Prevent copying of Scope objects.
      SafeForTerminationScope(const SafeForTerminationScope&) = delete;
      SafeForTerminationScope& operator=(const SafeForTerminationScope&) = delete;
  
     private:
      internal::Isolate* isolate_;
      bool prev_value_;
    };
  
    /**
     * Types of garbage collections that can be requested via
     * RequestGarbageCollectionForTesting.
     */
    enum GarbageCollectionType {
      kFullGarbageCollection,
      kMinorGarbageCollection
    };
  
    /**
     * Features reported via the SetUseCounterCallback callback. Do not change
     * assigned numbers of existing items; add new features to the end of this
     * list.
     */
    enum UseCounterFeature {
      kUseAsm = 0,
      kBreakIterator = 1,
      kLegacyConst = 2,
      kMarkDequeOverflow = 3,
      kStoreBufferOverflow = 4,
      kSlotsBufferOverflow = 5,
      kObjectObserve = 6,
      kForcedGC = 7,
      kSloppyMode = 8,
      kStrictMode = 9,
      kStrongMode = 10,
      kRegExpPrototypeStickyGetter = 11,
      kRegExpPrototypeToString = 12,
      kRegExpPrototypeUnicodeGetter = 13,
      kIntlV8Parse = 14,
      kIntlPattern = 15,
      kIntlResolved = 16,
      kPromiseChain = 17,
      kPromiseAccept = 18,
      kPromiseDefer = 19,
      kHtmlCommentInExternalScript = 20,
      kHtmlComment = 21,
      kSloppyModeBlockScopedFunctionRedefinition = 22,
      kForInInitializer = 23,
      kArrayProtectorDirtied = 24,
      kArraySpeciesModified = 25,
      kArrayPrototypeConstructorModified = 26,
      kArrayInstanceProtoModified = 27,
      kArrayInstanceConstructorModified = 28,
      kLegacyFunctionDeclaration = 29,
      kRegExpPrototypeSourceGetter = 30,
      kRegExpPrototypeOldFlagGetter = 31,
      kDecimalWithLeadingZeroInStrictMode = 32,
      kLegacyDateParser = 33,
      kDefineGetterOrSetterWouldThrow = 34,
      kFunctionConstructorReturnedUndefined = 35,
      kAssigmentExpressionLHSIsCallInSloppy = 36,
      kAssigmentExpressionLHSIsCallInStrict = 37,
      kPromiseConstructorReturnedUndefined = 38,
      kConstructorNonUndefinedPrimitiveReturn = 39,
      kLabeledExpressionStatement = 40,
      kLineOrParagraphSeparatorAsLineTerminator = 41,
      kIndexAccessor = 42,
      kErrorCaptureStackTrace = 43,
      kErrorPrepareStackTrace = 44,
      kErrorStackTraceLimit = 45,
      kWebAssemblyInstantiation = 46,
      kDeoptimizerDisableSpeculation = 47,
      kArrayPrototypeSortJSArrayModifiedPrototype = 48,
      kFunctionTokenOffsetTooLongForToString = 49,
      kWasmSharedMemory = 50,
      kWasmThreadOpcodes = 51,
      kAtomicsNotify = 52,
      kAtomicsWake = 53,
      kCollator = 54,
      kNumberFormat = 55,
      kDateTimeFormat = 56,
      kPluralRules = 57,
      kRelativeTimeFormat = 58,
      kLocale = 59,
      kListFormat = 60,
      kSegmenter = 61,
      kStringLocaleCompare = 62,
      kStringToLocaleUpperCase = 63,
      kStringToLocaleLowerCase = 64,
      kNumberToLocaleString = 65,
      kDateToLocaleString = 66,
      kDateToLocaleDateString = 67,
      kDateToLocaleTimeString = 68,
      kAttemptOverrideReadOnlyOnPrototypeSloppy = 69,
      kAttemptOverrideReadOnlyOnPrototypeStrict = 70,
      kOptimizedFunctionWithOneShotBytecode = 71,
      kRegExpMatchIsTrueishOnNonJSRegExp = 72,
      kRegExpMatchIsFalseishOnJSRegExp = 73,
      kDateGetTimezoneOffset = 74,
      kStringNormalize = 75,
  
      // If you add new values here, you'll also need to update Chromium's:
      // web_feature.mojom, UseCounterCallback.cpp, and enums.xml. V8 changes to
      // this list need to be landed first, then changes on the Chromium side.
      kUseCounterFeatureCount  // This enum value must be last.
    };
  
    enum MessageErrorLevel {
      kMessageLog = (1 << 0),
      kMessageDebug = (1 << 1),
      kMessageInfo = (1 << 2),
      kMessageError = (1 << 3),
      kMessageWarning = (1 << 4),
      kMessageAll = kMessageLog | kMessageDebug | kMessageInfo | kMessageError |
                    kMessageWarning,
    };
  
    typedef void (*UseCounterCallback)(Isolate* isolate,
                                       UseCounterFeature feature);
  
    /**
     * Allocates a new isolate but does not initialize it. Does not change the
     * currently entered isolate.
     *
     * Only Isolate::GetData() and Isolate::SetData(), which access the
     * embedder-controlled parts of the isolate, are allowed to be called on the
     * uninitialized isolate. To initialize the isolate, call
     * Isolate::Initialize().
     *
     * When an isolate is no longer used its resources should be freed
     * by calling Dispose().  Using the delete operator is not allowed.
     *
     * V8::Initialize() must have run prior to this.
     */
    static Isolate* Allocate();
  
    /**
     * Initialize an Isolate previously allocated by Isolate::Allocate().
     */
    static void Initialize(Isolate* isolate, const CreateParams& params);
  
    /**
     * Creates a new isolate.  Does not change the currently entered
     * isolate.
     *
     * When an isolate is no longer used its resources should be freed
     * by calling Dispose().  Using the delete operator is not allowed.
     *
     * V8::Initialize() must have run prior to this.
     */
    static Isolate* New(const CreateParams& params);
  
    /**
     * Returns the entered isolate for the current thread or NULL in
     * case there is no current isolate.
     *
     * This method must not be invoked before V8::Initialize() was invoked.
     */
    static Isolate* GetCurrent();
  
    /**
     * Custom callback used by embedders to help V8 determine if it should abort
     * when it throws and no internal handler is predicted to catch the
     * exception. If --abort-on-uncaught-exception is used on the command line,
     * then V8 will abort if either:
     * - no custom callback is set.
     * - the custom callback set returns true.
     * Otherwise, the custom callback will not be called and V8 will not abort.
     */
    typedef bool (*AbortOnUncaughtExceptionCallback)(Isolate*);
    void SetAbortOnUncaughtExceptionCallback(
        AbortOnUncaughtExceptionCallback callback);
  
    /**
     * This specifies the callback called by the upcoming dynamic
     * import() language feature to load modules.
     */
    void SetHostImportModuleDynamicallyCallback(
        HostImportModuleDynamicallyCallback callback);
  
    /**
     * This specifies the callback called by the upcoming importa.meta
     * language feature to retrieve host-defined meta data for a module.
     */
    void SetHostInitializeImportMetaObjectCallback(
        HostInitializeImportMetaObjectCallback callback);
  
    /**
     * This specifies the callback called when the stack property of Error
     * is accessed.
     */
    void SetPrepareStackTraceCallback(PrepareStackTraceCallback callback);
  
    /**
     * Optional notification that the system is running low on memory.
     * V8 uses these notifications to guide heuristics.
     * It is allowed to call this function from another thread while
     * the isolate is executing long running JavaScript code.
     */
    void MemoryPressureNotification(MemoryPressureLevel level);
  
    /**
     * Methods below this point require holding a lock (using Locker) in
     * a multi-threaded environment.
     */
  
    /**
     * Sets this isolate as the entered one for the current thread.
     * Saves the previously entered one (if any), so that it can be
     * restored when exiting.  Re-entering an isolate is allowed.
     */
    void Enter();
  
    /**
     * Exits this isolate by restoring the previously entered one in the
     * current thread.  The isolate may still stay the same, if it was
     * entered more than once.
     *
     * Requires: this == Isolate::GetCurrent().
     */
    void Exit();
  
    /**
     * Disposes the isolate.  The isolate must not be entered by any
     * thread to be disposable.
     */
    void Dispose();
  
    /**
     * Dumps activated low-level V8 internal stats. This can be used instead
     * of performing a full isolate disposal.
     */
    void DumpAndResetStats();
  
    /**
     * Discards all V8 thread-specific data for the Isolate. Should be used
     * if a thread is terminating and it has used an Isolate that will outlive
     * the thread -- all thread-specific data for an Isolate is discarded when
     * an Isolate is disposed so this call is pointless if an Isolate is about
     * to be Disposed.
     */
    void DiscardThreadSpecificMetadata();
  
    /**
     * Associate embedder-specific data with the isolate. |slot| has to be
     * between 0 and GetNumberOfDataSlots() - 1.
     */
    V8_INLINE void SetData(uint32_t slot, void* data);
  
    /**
     * Retrieve embedder-specific data from the isolate.
     * Returns NULL if SetData has never been called for the given |slot|.
     */
    V8_INLINE void* GetData(uint32_t slot);
  
    /**
     * Returns the maximum number of available embedder data slots. Valid slots
     * are in the range of 0 - GetNumberOfDataSlots() - 1.
     */
    V8_INLINE static uint32_t GetNumberOfDataSlots();
  
    /**
     * Return data that was previously attached to the isolate snapshot via
     * SnapshotCreator, and removes the reference to it.
     * Repeated call with the same index returns an empty MaybeLocal.
     */
    template <class T>
    V8_INLINE MaybeLocal<T> GetDataFromSnapshotOnce(size_t index);
  
    /**
     * Get statistics about the heap memory usage.
     */
    void GetHeapStatistics(HeapStatistics* heap_statistics);
  
    /**
     * Returns the number of spaces in the heap.
     */
    size_t NumberOfHeapSpaces();
  
    /**
     * Get the memory usage of a space in the heap.
     *
     * \param space_statistics The HeapSpaceStatistics object to fill in
     *   statistics.
     * \param index The index of the space to get statistics from, which ranges
     *   from 0 to NumberOfHeapSpaces() - 1.
     * \returns true on success.
     */
    bool GetHeapSpaceStatistics(HeapSpaceStatistics* space_statistics,
                                size_t index);
  
    /**
     * Returns the number of types of objects tracked in the heap at GC.
     */
    size_t NumberOfTrackedHeapObjectTypes();
  
    /**
     * Get statistics about objects in the heap.
     *
     * \param object_statistics The HeapObjectStatistics object to fill in
     *   statistics of objects of given type, which were live in the previous GC.
     * \param type_index The index of the type of object to fill details about,
     *   which ranges from 0 to NumberOfTrackedHeapObjectTypes() - 1.
     * \returns true on success.
     */
    bool GetHeapObjectStatisticsAtLastGC(HeapObjectStatistics* object_statistics,
                                         size_t type_index);
  
    /**
     * Get statistics about code and its metadata in the heap.
     *
     * \param object_statistics The HeapCodeStatistics object to fill in
     *   statistics of code, bytecode and their metadata.
     * \returns true on success.
     */
    bool GetHeapCodeAndMetadataStatistics(HeapCodeStatistics* object_statistics);
  
    /**
     * Get a call stack sample from the isolate.
     * \param state Execution state.
     * \param frames Caller allocated buffer to store stack frames.
     * \param frames_limit Maximum number of frames to capture. The buffer must
     *                     be large enough to hold the number of frames.
     * \param sample_info The sample info is filled up by the function
     *                    provides number of actual captured stack frames and
     *                    the current VM state.
     * \note GetStackSample should only be called when the JS thread is paused or
     *       interrupted. Otherwise the behavior is undefined.
     */
    void GetStackSample(const RegisterState& state, void** frames,
                        size_t frames_limit, SampleInfo* sample_info);
  
    /**
     * Adjusts the amount of registered external memory. Used to give V8 an
     * indication of the amount of externally allocated memory that is kept alive
     * by JavaScript objects. V8 uses this to decide when to perform global
     * garbage collections. Registering externally allocated memory will trigger
     * global garbage collections more often than it would otherwise in an attempt
     * to garbage collect the JavaScript objects that keep the externally
     * allocated memory alive.
     *
     * \param change_in_bytes the change in externally allocated memory that is
     *   kept alive by JavaScript objects.
     * \returns the adjusted value.
     */
    V8_INLINE int64_t
        AdjustAmountOfExternalAllocatedMemory(int64_t change_in_bytes);
  
    /**
     * Returns the number of phantom handles without callbacks that were reset
     * by the garbage collector since the last call to this function.
     */
    size_t NumberOfPhantomHandleResetsSinceLastCall();
  
    /**
     * Returns heap profiler for this isolate. Will return NULL until the isolate
     * is initialized.
     */
    HeapProfiler* GetHeapProfiler();
  
    /**
     * Tells the VM whether the embedder is idle or not.
     */
    void SetIdle(bool is_idle);
  
    /** Returns the ArrayBuffer::Allocator used in this isolate. */
    ArrayBuffer::Allocator* GetArrayBufferAllocator();
  
    /** Returns true if this isolate has a current context. */
    bool InContext();
  
    /**
     * Returns the context of the currently running JavaScript, or the context
     * on the top of the stack if no JavaScript is running.
     */
    Local<Context> GetCurrentContext();
  
    /** Returns the last context entered through V8's C++ API. */
    V8_DEPRECATED("Use GetEnteredOrMicrotaskContext().",
                  Local<Context> GetEnteredContext());
  
    /**
     * Returns either the last context entered through V8's C++ API, or the
     * context of the currently running microtask while processing microtasks.
     * If a context is entered while executing a microtask, that context is
     * returned.
     */
    Local<Context> GetEnteredOrMicrotaskContext();
  
    /**
     * Returns the Context that corresponds to the Incumbent realm in HTML spec.
     * https://html.spec.whatwg.org/multipage/webappapis.html#incumbent
     */
    Local<Context> GetIncumbentContext();
  
    /**
     * Schedules an exception to be thrown when returning to JavaScript.  When an
     * exception has been scheduled it is illegal to invoke any JavaScript
     * operation; the caller must return immediately and only after the exception
     * has been handled does it become legal to invoke JavaScript operations.
     */
    Local<Value> ThrowException(Local<Value> exception);
  
    typedef void (*GCCallback)(Isolate* isolate, GCType type,
                               GCCallbackFlags flags);
    typedef void (*GCCallbackWithData)(Isolate* isolate, GCType type,
                                       GCCallbackFlags flags, void* data);
  
    /**
     * Enables the host application to receive a notification before a
     * garbage collection. Allocations are allowed in the callback function,
     * but the callback is not re-entrant: if the allocation inside it will
     * trigger the garbage collection, the callback won't be called again.
     * It is possible to specify the GCType filter for your callback. But it is
     * not possible to register the same callback function two times with
     * different GCType filters.
     */
    void AddGCPrologueCallback(GCCallbackWithData callback, void* data = nullptr,
                               GCType gc_type_filter = kGCTypeAll);
    void AddGCPrologueCallback(GCCallback callback,
                               GCType gc_type_filter = kGCTypeAll);
  
    /**
     * This function removes callback which was installed by
     * AddGCPrologueCallback function.
     */
    void RemoveGCPrologueCallback(GCCallbackWithData, void* data = nullptr);
    void RemoveGCPrologueCallback(GCCallback callback);
  
    /**
     * Sets the embedder heap tracer for the isolate.
     */
    void SetEmbedderHeapTracer(EmbedderHeapTracer* tracer);
  
    /*
     * Gets the currently active heap tracer for the isolate.
     */
    EmbedderHeapTracer* GetEmbedderHeapTracer();
  
    /**
     * Use for |AtomicsWaitCallback| to indicate the type of event it receives.
     */
    enum class AtomicsWaitEvent {
      /** Indicates that this call is happening before waiting. */
      kStartWait,
      /** `Atomics.wait()` finished because of an `Atomics.wake()` call. */
      kWokenUp,
      /** `Atomics.wait()` finished because it timed out. */
      kTimedOut,
      /** `Atomics.wait()` was interrupted through |TerminateExecution()|. */
      kTerminatedExecution,
      /** `Atomics.wait()` was stopped through |AtomicsWaitWakeHandle|. */
      kAPIStopped,
      /** `Atomics.wait()` did not wait, as the initial condition was not met. */
      kNotEqual
    };
  
    /**
     * Passed to |AtomicsWaitCallback| as a means of stopping an ongoing
     * `Atomics.wait` call.
     */
    class V8_EXPORT AtomicsWaitWakeHandle {
     public:
      /**
       * Stop this `Atomics.wait()` call and call the |AtomicsWaitCallback|
       * with |kAPIStopped|.
       *
       * This function may be called from another thread. The caller has to ensure
       * through proper synchronization that it is not called after
       * the finishing |AtomicsWaitCallback|.
       *
       * Note that the ECMAScript specification does not plan for the possibility
       * of wakeups that are neither coming from a timeout or an `Atomics.wake()`
       * call, so this may invalidate assumptions made by existing code.
       * The embedder may accordingly wish to schedule an exception in the
       * finishing |AtomicsWaitCallback|.
       */
      void Wake();
    };
  
    /**
     * Embedder callback for `Atomics.wait()` that can be added through
     * |SetAtomicsWaitCallback|.
     *
     * This will be called just before starting to wait with the |event| value
     * |kStartWait| and after finishing waiting with one of the other
     * values of |AtomicsWaitEvent| inside of an `Atomics.wait()` call.
     *
     * |array_buffer| will refer to the underlying SharedArrayBuffer,
     * |offset_in_bytes| to the location of the waited-on memory address inside
     * the SharedArrayBuffer.
     *
     * |value| and |timeout_in_ms| will be the values passed to
     * the `Atomics.wait()` call. If no timeout was used, |timeout_in_ms|
     * will be `INFINITY`.
     *
     * In the |kStartWait| callback, |stop_handle| will be an object that
     * is only valid until the corresponding finishing callback and that
     * can be used to stop the wait process while it is happening.
     *
     * This callback may schedule exceptions, *unless* |event| is equal to
     * |kTerminatedExecution|.
     */
    typedef void (*AtomicsWaitCallback)(AtomicsWaitEvent event,
                                        Local<SharedArrayBuffer> array_buffer,
                                        size_t offset_in_bytes, int64_t value,
                                        double timeout_in_ms,
                                        AtomicsWaitWakeHandle* stop_handle,
                                        void* data);
  
    /**
     * Set a new |AtomicsWaitCallback|. This overrides an earlier
     * |AtomicsWaitCallback|, if there was any. If |callback| is nullptr,
     * this unsets the callback. |data| will be passed to the callback
     * as its last parameter.
     */
    void SetAtomicsWaitCallback(AtomicsWaitCallback callback, void* data);
  
    /**
     * Enables the host application to receive a notification after a
     * garbage collection. Allocations are allowed in the callback function,
     * but the callback is not re-entrant: if the allocation inside it will
     * trigger the garbage collection, the callback won't be called again.
     * It is possible to specify the GCType filter for your callback. But it is
     * not possible to register the same callback function two times with
     * different GCType filters.
     */
    void AddGCEpilogueCallback(GCCallbackWithData callback, void* data = nullptr,
                               GCType gc_type_filter = kGCTypeAll);
    void AddGCEpilogueCallback(GCCallback callback,
                               GCType gc_type_filter = kGCTypeAll);
  
    /**
     * This function removes callback which was installed by
     * AddGCEpilogueCallback function.
     */
    void RemoveGCEpilogueCallback(GCCallbackWithData callback,
                                  void* data = nullptr);
    void RemoveGCEpilogueCallback(GCCallback callback);
  
    typedef size_t (*GetExternallyAllocatedMemoryInBytesCallback)();
  
    /**
     * Set the callback that tells V8 how much memory is currently allocated
     * externally of the V8 heap. Ideally this memory is somehow connected to V8
     * objects and may get freed-up when the corresponding V8 objects get
     * collected by a V8 garbage collection.
     */
    void SetGetExternallyAllocatedMemoryInBytesCallback(
        GetExternallyAllocatedMemoryInBytesCallback callback);
  
    /**
     * Forcefully terminate the current thread of JavaScript execution
     * in the given isolate.
     *
     * This method can be used by any thread even if that thread has not
     * acquired the V8 lock with a Locker object.
     */
    void TerminateExecution();
  
    /**
     * Is V8 terminating JavaScript execution.
     *
     * Returns true if JavaScript execution is currently terminating
     * because of a call to TerminateExecution.  In that case there are
     * still JavaScript frames on the stack and the termination
     * exception is still active.
     */
    bool IsExecutionTerminating();
  
    /**
     * Resume execution capability in the given isolate, whose execution
     * was previously forcefully terminated using TerminateExecution().
     *
     * When execution is forcefully terminated using TerminateExecution(),
     * the isolate can not resume execution until all JavaScript frames
     * have propagated the uncatchable exception which is generated.  This
     * method allows the program embedding the engine to handle the
     * termination event and resume execution capability, even if
     * JavaScript frames remain on the stack.
     *
     * This method can be used by any thread even if that thread has not
     * acquired the V8 lock with a Locker object.
     */
    void CancelTerminateExecution();
  
    /**
     * Request V8 to interrupt long running JavaScript code and invoke
     * the given |callback| passing the given |data| to it. After |callback|
     * returns control will be returned to the JavaScript code.
     * There may be a number of interrupt requests in flight.
     * Can be called from another thread without acquiring a |Locker|.
     * Registered |callback| must not reenter interrupted Isolate.
     */
    void RequestInterrupt(InterruptCallback callback, void* data);
  
    /**
     * Request garbage collection in this Isolate. It is only valid to call this
     * function if --expose_gc was specified.
     *
     * This should only be used for testing purposes and not to enforce a garbage
     * collection schedule. It has strong negative impact on the garbage
     * collection performance. Use IdleNotificationDeadline() or
     * LowMemoryNotification() instead to influence the garbage collection
     * schedule.
     */
    void RequestGarbageCollectionForTesting(GarbageCollectionType type);
  
    /**
     * Set the callback to invoke for logging event.
     */
    void SetEventLogger(LogEventCallback that);
  
    /**
     * Adds a callback to notify the host application right before a script
     * is about to run. If a script re-enters the runtime during executing, the
     * BeforeCallEnteredCallback is invoked for each re-entrance.
     * Executing scripts inside the callback will re-trigger the callback.
     */
    void AddBeforeCallEnteredCallback(BeforeCallEnteredCallback callback);
  
    /**
     * Removes callback that was installed by AddBeforeCallEnteredCallback.
     */
    void RemoveBeforeCallEnteredCallback(BeforeCallEnteredCallback callback);
  
    /**
     * Adds a callback to notify the host application when a script finished
     * running.  If a script re-enters the runtime during executing, the
     * CallCompletedCallback is only invoked when the outer-most script
     * execution ends.  Executing scripts inside the callback do not trigger
     * further callbacks.
     */
    void AddCallCompletedCallback(CallCompletedCallback callback);
  
    /**
     * Removes callback that was installed by AddCallCompletedCallback.
     */
    void RemoveCallCompletedCallback(CallCompletedCallback callback);
  
    /**
     * Set the PromiseHook callback for various promise lifecycle
     * events.
     */
    void SetPromiseHook(PromiseHook hook);
  
    /**
     * Set callback to notify about promise reject with no handler, or
     * revocation of such a previous notification once the handler is added.
     */
    void SetPromiseRejectCallback(PromiseRejectCallback callback);
  
    /**
     * Runs the default MicrotaskQueue until it gets empty.
     * Any exceptions thrown by microtask callbacks are swallowed.
     */
    void RunMicrotasks();
  
    /**
     * Enqueues the callback to the default MicrotaskQueue
     */
    void EnqueueMicrotask(Local<Function> microtask);
  
    /**
     * Enqueues the callback to the default MicrotaskQueue
     */
    void EnqueueMicrotask(MicrotaskCallback callback, void* data = nullptr);
  
    /**
     * Controls how Microtasks are invoked. See MicrotasksPolicy for details.
     */
    void SetMicrotasksPolicy(MicrotasksPolicy policy);
  
    /**
     * Returns the policy controlling how Microtasks are invoked.
     */
    MicrotasksPolicy GetMicrotasksPolicy() const;
  
    /**
     * Adds a callback to notify the host application after
     * microtasks were run on the default MicrotaskQueue. The callback is
     * triggered by explicit RunMicrotasks call or automatic microtasks execution
     * (see SetMicrotaskPolicy).
     *
     * Callback will trigger even if microtasks were attempted to run,
     * but the microtasks queue was empty and no single microtask was actually
     * executed.
     *
     * Executing scripts inside the callback will not re-trigger microtasks and
     * the callback.
     */
    V8_DEPRECATE_SOON("Use *WithData version.",
                      void AddMicrotasksCompletedCallback(
                          MicrotasksCompletedCallback callback));
    void AddMicrotasksCompletedCallback(
        MicrotasksCompletedCallbackWithData callback, void* data = nullptr);
  
    /**
     * Removes callback that was installed by AddMicrotasksCompletedCallback.
     */
    V8_DEPRECATE_SOON("Use *WithData version.",
                      void RemoveMicrotasksCompletedCallback(
                          MicrotasksCompletedCallback callback));
    void RemoveMicrotasksCompletedCallback(
        MicrotasksCompletedCallbackWithData callback, void* data = nullptr);
  
    /**
     * Sets a callback for counting the number of times a feature of V8 is used.
     */
    void SetUseCounterCallback(UseCounterCallback callback);
  
    /**
     * Enables the host application to provide a mechanism for recording
     * statistics counters.
     */
    void SetCounterFunction(CounterLookupCallback);
  
    /**
     * Enables the host application to provide a mechanism for recording
     * histograms. The CreateHistogram function returns a
     * histogram which will later be passed to the AddHistogramSample
     * function.
     */
    void SetCreateHistogramFunction(CreateHistogramCallback);
    void SetAddHistogramSampleFunction(AddHistogramSampleCallback);
  
    /**
     * Optional notification that the embedder is idle.
     * V8 uses the notification to perform garbage collection.
     * This call can be used repeatedly if the embedder remains idle.
     * Returns true if the embedder should stop calling IdleNotificationDeadline
     * until real work has been done.  This indicates that V8 has done
     * as much cleanup as it will be able to do.
     *
     * The deadline_in_seconds argument specifies the deadline V8 has to finish
     * garbage collection work. deadline_in_seconds is compared with
     * MonotonicallyIncreasingTime() and should be based on the same timebase as
     * that function. There is no guarantee that the actual work will be done
     * within the time limit.
     */
    bool IdleNotificationDeadline(double deadline_in_seconds);
  
    /**
     * Optional notification that the system is running low on memory.
     * V8 uses these notifications to attempt to free memory.
     */
    void LowMemoryNotification();
  
    /**
     * Optional notification that a context has been disposed. V8 uses
     * these notifications to guide the GC heuristic. Returns the number
     * of context disposals - including this one - since the last time
     * V8 had a chance to clean up.
     *
     * The optional parameter |dependant_context| specifies whether the disposed
     * context was depending on state from other contexts or not.
     */
    int ContextDisposedNotification(bool dependant_context = true);
  
    /**
     * Optional notification that the isolate switched to the foreground.
     * V8 uses these notifications to guide heuristics.
     */
    void IsolateInForegroundNotification();
  
    /**
     * Optional notification that the isolate switched to the background.
     * V8 uses these notifications to guide heuristics.
     */
    void IsolateInBackgroundNotification();
  
    /**
     * Optional notification which will enable the memory savings mode.
     * V8 uses this notification to guide heuristics which may result in a
     * smaller memory footprint at the cost of reduced runtime performance.
     */
    void EnableMemorySavingsMode();
  
    /**
     * Optional notification which will disable the memory savings mode.
     */
    void DisableMemorySavingsMode();
  
    /**
     * Optional notification to tell V8 the current performance requirements
     * of the embedder based on RAIL.
     * V8 uses these notifications to guide heuristics.
     * This is an unfinished experimental feature. Semantics and implementation
     * may change frequently.
     */
    void SetRAILMode(RAILMode rail_mode);
  
    /**
     * Optional notification to tell V8 the current isolate is used for debugging
     * and requires higher heap limit.
     */
    void IncreaseHeapLimitForDebugging();
  
    /**
     * Restores the original heap limit after IncreaseHeapLimitForDebugging().
     */
    void RestoreOriginalHeapLimit();
  
    /**
     * Returns true if the heap limit was increased for debugging and the
     * original heap limit was not restored yet.
     */
    bool IsHeapLimitIncreasedForDebugging();
  
    /**
     * Allows the host application to provide the address of a function that is
     * notified each time code is added, moved or removed.
     *
     * \param options options for the JIT code event handler.
     * \param event_handler the JIT code event handler, which will be invoked
     *     each time code is added, moved or removed.
     * \note \p event_handler won't get notified of existent code.
     * \note since code removal notifications are not currently issued, the
     *     \p event_handler may get notifications of code that overlaps earlier
     *     code notifications. This happens when code areas are reused, and the
     *     earlier overlapping code areas should therefore be discarded.
     * \note the events passed to \p event_handler and the strings they point to
     *     are not guaranteed to live past each call. The \p event_handler must
     *     copy strings and other parameters it needs to keep around.
     * \note the set of events declared in JitCodeEvent::EventType is expected to
     *     grow over time, and the JitCodeEvent structure is expected to accrue
     *     new members. The \p event_handler function must ignore event codes
     *     it does not recognize to maintain future compatibility.
     * \note Use Isolate::CreateParams to get events for code executed during
     *     Isolate setup.
     */
    void SetJitCodeEventHandler(JitCodeEventOptions options,
                                JitCodeEventHandler event_handler);
  
    /**
     * Modifies the stack limit for this Isolate.
     *
     * \param stack_limit An address beyond which the Vm's stack may not grow.
     *
     * \note  If you are using threads then you should hold the V8::Locker lock
     *     while setting the stack limit and you must set a non-default stack
     *     limit separately for each thread.
     */
    void SetStackLimit(uintptr_t stack_limit);
  
    /**
     * Returns a memory range that can potentially contain jitted code. Code for
     * V8's 'builtins' will not be in this range if embedded builtins is enabled.
     *
     * On Win64, embedders are advised to install function table callbacks for
     * these ranges, as default SEH won't be able to unwind through jitted code.
     * The first page of the code range is reserved for the embedder and is
     * committed, writable, and executable, to be used to store unwind data, as
     * documented in
     * https://docs.microsoft.com/en-us/cpp/build/exception-handling-x64.
     *
     * Might be empty on other platforms.
     *
     * https://code.google.com/p/v8/issues/detail?id=3598
     */
    void GetCodeRange(void** start, size_t* length_in_bytes);
  
    /**
     * Returns the UnwindState necessary for use with the Unwinder API.
     */
    UnwindState GetUnwindState();
  
    /** Set the callback to invoke in case of fatal errors. */
    void SetFatalErrorHandler(FatalErrorCallback that);
  
    /** Set the callback to invoke in case of OOM errors. */
    void SetOOMErrorHandler(OOMErrorCallback that);
  
    /**
     * Add a callback to invoke in case the heap size is close to the heap limit.
     * If multiple callbacks are added, only the most recently added callback is
     * invoked.
     */
    void AddNearHeapLimitCallback(NearHeapLimitCallback callback, void* data);
  
    /**
     * Remove the given callback and restore the heap limit to the
     * given limit. If the given limit is zero, then it is ignored.
     * If the current heap size is greater than the given limit,
     * then the heap limit is restored to the minimal limit that
     * is possible for the current heap size.
     */
    void RemoveNearHeapLimitCallback(NearHeapLimitCallback callback,
                                     size_t heap_limit);
  
    /**
     * If the heap limit was changed by the NearHeapLimitCallback, then the
     * initial heap limit will be restored once the heap size falls below the
     * given threshold percentage of the initial heap limit.
     * The threshold percentage is a number in (0.0, 1.0) range.
     */
    void AutomaticallyRestoreInitialHeapLimit(double threshold_percent = 0.5);
  
    /**
     * Set the callback to invoke to check if code generation from
     * strings should be allowed.
     */
    void SetAllowCodeGenerationFromStringsCallback(
        AllowCodeGenerationFromStringsCallback callback);
  
    /**
     * Set the callback to invoke to check if wasm code generation should
     * be allowed.
     */
    void SetAllowWasmCodeGenerationCallback(
        AllowWasmCodeGenerationCallback callback);
  
    /**
     * Embedder over{ride|load} injection points for wasm APIs. The expectation
     * is that the embedder sets them at most once.
     */
    void SetWasmModuleCallback(ExtensionCallback callback);
    void SetWasmInstanceCallback(ExtensionCallback callback);
  
    void SetWasmStreamingCallback(WasmStreamingCallback callback);
  
    void SetWasmThreadsEnabledCallback(WasmThreadsEnabledCallback callback);
  
    /**
    * Check if V8 is dead and therefore unusable.  This is the case after
    * fatal errors such as out-of-memory situations.
    */
    bool IsDead();
  
    /**
     * Adds a message listener (errors only).
     *
     * The same message listener can be added more than once and in that
     * case it will be called more than once for each message.
     *
     * If data is specified, it will be passed to the callback when it is called.
     * Otherwise, the exception object will be passed to the callback instead.
     */
    bool AddMessageListener(MessageCallback that,
                            Local<Value> data = Local<Value>());
  
    /**
     * Adds a message listener.
     *
     * The same message listener can be added more than once and in that
     * case it will be called more than once for each message.
     *
     * If data is specified, it will be passed to the callback when it is called.
     * Otherwise, the exception object will be passed to the callback instead.
     *
     * A listener can listen for particular error levels by providing a mask.
     */
    bool AddMessageListenerWithErrorLevel(MessageCallback that,
                                          int message_levels,
                                          Local<Value> data = Local<Value>());
  
    /**
     * Remove all message listeners from the specified callback function.
     */
    void RemoveMessageListeners(MessageCallback that);
  
    /** Callback function for reporting failed access checks.*/
    void SetFailedAccessCheckCallbackFunction(FailedAccessCheckCallback);
  
    /**
     * Tells V8 to capture current stack trace when uncaught exception occurs
     * and report it to the message listeners. The option is off by default.
     */
    void SetCaptureStackTraceForUncaughtExceptions(
        bool capture, int frame_limit = 10,
        StackTrace::StackTraceOptions options = StackTrace::kOverview);
  
    /**
     * Iterates through all external resources referenced from current isolate
     * heap.  GC is not invoked prior to iterating, therefore there is no
     * guarantee that visited objects are still alive.
     */
    void VisitExternalResources(ExternalResourceVisitor* visitor);
  
    /**
     * Iterates through all the persistent handles in the current isolate's heap
     * that have class_ids.
     */
    void VisitHandlesWithClassIds(PersistentHandleVisitor* visitor);
  
    /**
     * Iterates through all the persistent handles in the current isolate's heap
     * that have class_ids and are weak to be marked as inactive if there is no
     * pending activity for the handle.
     */
    void VisitWeakHandles(PersistentHandleVisitor* visitor);
  
    /**
     * Check if this isolate is in use.
     * True if at least one thread Enter'ed this isolate.
     */
    bool IsInUse();
  
    /**
     * Set whether calling Atomics.wait (a function that may block) is allowed in
     * this isolate. This can also be configured via
     * CreateParams::allow_atomics_wait.
     */
    void SetAllowAtomicsWait(bool allow);
  
    /**
     * Time zone redetection indicator for
     * DateTimeConfigurationChangeNotification.
     *
     * kSkip indicates V8 that the notification should not trigger redetecting
     * host time zone. kRedetect indicates V8 that host time zone should be
     * redetected, and used to set the default time zone.
     *
     * The host time zone detection may require file system access or similar
     * operations unlikely to be available inside a sandbox. If v8 is run inside a
     * sandbox, the host time zone has to be detected outside the sandbox before
     * calling DateTimeConfigurationChangeNotification function.
     */
    enum class TimeZoneDetection { kSkip, kRedetect };
  
    /**
     * Notification that the embedder has changed the time zone, daylight savings
     * time or other date / time configuration parameters. V8 keeps a cache of
     * various values used for date / time computation. This notification will
     * reset those cached values for the current context so that date / time
     * configuration changes would be reflected.
     *
     * This API should not be called more than needed as it will negatively impact
     * the performance of date operations.
     */
    void DateTimeConfigurationChangeNotification(
        TimeZoneDetection time_zone_detection = TimeZoneDetection::kSkip);
  
    /**
     * Notification that the embedder has changed the locale. V8 keeps a cache of
     * various values used for locale computation. This notification will reset
     * those cached values for the current context so that locale configuration
     * changes would be reflected.
     *
     * This API should not be called more than needed as it will negatively impact
     * the performance of locale operations.
     */
    void LocaleConfigurationChangeNotification();
  
    Isolate() = delete;
    ~Isolate() = delete;
    Isolate(const Isolate&) = delete;
    Isolate& operator=(const Isolate&) = delete;
    // Deleting operator new and delete here is allowed as ctor and dtor is also
    // deleted.
    void* operator new(size_t size) = delete;
    void* operator new[](size_t size) = delete;
    void operator delete(void*, size_t) = delete;
    void operator delete[](void*, size_t) = delete;
  
   private:
    template <class K, class V, class Traits>
    friend class PersistentValueMapBase;
  
    internal::Address* GetDataFromSnapshotOnce(size_t index);
    void ReportExternalAllocationLimitReached();
    void CheckMemoryPressure();
  };
  
  class V8_EXPORT StartupData {
   public:
    /**
     * Whether the data created can be rehashed and and the hash seed can be
     * recomputed when deserialized.
     * Only valid for StartupData returned by SnapshotCreator::CreateBlob().
     */
    bool CanBeRehashed() const;
  
    const char* data;
    int raw_size;
  };
  
  
  /**
   * EntropySource is used as a callback function when v8 needs a source
   * of entropy.
   */
  typedef bool (*EntropySource)(unsigned char* buffer, size_t length);
  
  /**
   * ReturnAddressLocationResolver is used as a callback function when v8 is
   * resolving the location of a return address on the stack. Profilers that
   * change the return address on the stack can use this to resolve the stack
   * location to wherever the profiler stashed the original return address.
   *
   * \param return_addr_location A location on stack where a machine
   *    return address resides.
   * \returns Either return_addr_location, or else a pointer to the profiler's
   *    copy of the original return address.
   *
   * \note The resolver function must not cause garbage collection.
   */
  typedef uintptr_t (*ReturnAddressLocationResolver)(
      uintptr_t return_addr_location);
  
  
  /**
   * Container class for static utility functions.
   */
  class V8_EXPORT V8 {
   public:
    /**
     * Hand startup data to V8, in case the embedder has chosen to build
     * V8 with external startup data.
     *
     * Note:
     * - By default the startup data is linked into the V8 library, in which
     *   case this function is not meaningful.
     * - If this needs to be called, it needs to be called before V8
     *   tries to make use of its built-ins.
     * - To avoid unnecessary copies of data, V8 will point directly into the
     *   given data blob, so pretty please keep it around until V8 exit.
     * - Compression of the startup blob might be useful, but needs to
     *   handled entirely on the embedders' side.
     * - The call will abort if the data is invalid.
     */
    static void SetNativesDataBlob(StartupData* startup_blob);
    static void SetSnapshotDataBlob(StartupData* startup_blob);
  
    /** Set the callback to invoke in case of Dcheck failures. */
    static void SetDcheckErrorHandler(DcheckErrorCallback that);
  
  
    /**
     * Sets V8 flags from a string.
     */
    static void SetFlagsFromString(const char* str);
    static void SetFlagsFromString(const char* str, size_t length);
    V8_DEPRECATED("use size_t version",
                  static void SetFlagsFromString(const char* str, int length));
  
    /**
     * Sets V8 flags from the command line.
     */
    static void SetFlagsFromCommandLine(int* argc,
                                        char** argv,
                                        bool remove_flags);
  
    /** Get the version string. */
    static const char* GetVersion();
  
    /**
     * Initializes V8. This function needs to be called before the first Isolate
     * is created. It always returns true.
     */
    static bool Initialize();
  
    /**
     * Allows the host application to provide a callback which can be used
     * as a source of entropy for random number generators.
     */
    static void SetEntropySource(EntropySource source);
  
    /**
     * Allows the host application to provide a callback that allows v8 to
     * cooperate with a profiler that rewrites return addresses on stack.
     */
    static void SetReturnAddressLocationResolver(
        ReturnAddressLocationResolver return_address_resolver);
  
    /**
     * Releases any resources used by v8 and stops any utility threads
     * that may be running.  Note that disposing v8 is permanent, it
     * cannot be reinitialized.
     *
     * It should generally not be necessary to dispose v8 before exiting
     * a process, this should happen automatically.  It is only necessary
     * to use if the process needs the resources taken up by v8.
     */
    static bool Dispose();
  
    /**
     * Initialize the ICU library bundled with V8. The embedder should only
     * invoke this method when using the bundled ICU. Returns true on success.
     *
     * If V8 was compiled with the ICU data in an external file, the location
     * of the data file has to be provided.
     */
    static bool InitializeICU(const char* icu_data_file = nullptr);
  
    /**
     * Initialize the ICU library bundled with V8. The embedder should only
     * invoke this method when using the bundled ICU. If V8 was compiled with
     * the ICU data in an external file and when the default location of that
     * file should be used, a path to the executable must be provided.
     * Returns true on success.
     *
     * The default is a file called icudtl.dat side-by-side with the executable.
     *
     * Optionally, the location of the data file can be provided to override the
     * default.
     */
    static bool InitializeICUDefaultLocation(const char* exec_path,
                                             const char* icu_data_file = nullptr);
  
    /**
     * Initialize the external startup data. The embedder only needs to
     * invoke this method when external startup data was enabled in a build.
     *
     * If V8 was compiled with the startup data in an external file, then
     * V8 needs to be given those external files during startup. There are
     * three ways to do this:
     * - InitializeExternalStartupData(const char*)
     *   This will look in the given directory for files "natives_blob.bin"
     *   and "snapshot_blob.bin" - which is what the default build calls them.
     * - InitializeExternalStartupData(const char*, const char*)
     *   As above, but will directly use the two given file names.
     * - Call SetNativesDataBlob, SetNativesDataBlob.
     *   This will read the blobs from the given data structures and will
     *   not perform any file IO.
     */
    static void InitializeExternalStartupData(const char* directory_path);
    static void InitializeExternalStartupData(const char* natives_blob,
                                              const char* snapshot_blob);
    /**
     * Sets the v8::Platform to use. This should be invoked before V8 is
     * initialized.
     */
    static void InitializePlatform(Platform* platform);
  
    /**
     * Clears all references to the v8::Platform. This should be invoked after
     * V8 was disposed.
     */
    static void ShutdownPlatform();
  
  #if V8_OS_POSIX
    /**
     * Give the V8 signal handler a chance to handle a fault.
     *
     * This function determines whether a memory access violation can be recovered
     * by V8. If so, it will return true and modify context to return to a code
     * fragment that can recover from the fault. Otherwise, TryHandleSignal will
     * return false.
     *
     * The parameters to this function correspond to those passed to a Linux
     * signal handler.
     *
     * \param signal_number The signal number.
     *
     * \param info A pointer to the siginfo_t structure provided to the signal
     * handler.
     *
     * \param context The third argument passed to the Linux signal handler, which
     * points to a ucontext_t structure.
     */
    V8_DEPRECATE_SOON("Use TryHandleWebAssemblyTrapPosix",
                      static bool TryHandleSignal(int signal_number, void* info,
                                                  void* context));
  #endif  // V8_OS_POSIX
  
    /**
     * Activate trap-based bounds checking for WebAssembly.
     *
     * \param use_v8_signal_handler Whether V8 should install its own signal
     * handler or rely on the embedder's.
     */
    static bool EnableWebAssemblyTrapHandler(bool use_v8_signal_handler);
  
  #if defined(V8_OS_WIN)
    /**
     * On Win64, by default V8 does not emit unwinding data for jitted code,
     * which means the OS cannot walk the stack frames and the system Structured
     * Exception Handling (SEH) cannot unwind through V8-generated code:
     * https://code.google.com/p/v8/issues/detail?id=3598.
     *
     * This function allows embedders to register a custom exception handler for
     * exceptions in V8-generated code.
     */
    static void SetUnhandledExceptionCallback(
        UnhandledExceptionCallback unhandled_exception_callback);
  #endif
  
   private:
    V8();
  
    static internal::Address* GlobalizeReference(internal::Isolate* isolate,
                                                 internal::Address* handle);
    static internal::Address* GlobalizeTracedReference(internal::Isolate* isolate,
                                                       internal::Address* handle,
                                                       internal::Address* slot);
    static void MoveGlobalReference(internal::Address** from,
                                    internal::Address** to);
    static void MoveTracedGlobalReference(internal::Address** from,
                                          internal::Address** to);
    static internal::Address* CopyGlobalReference(internal::Address* from);
    static void DisposeGlobal(internal::Address* global_handle);
    static void DisposeTracedGlobal(internal::Address* global_handle);
    static void MakeWeak(internal::Address* location, void* data,
                         WeakCallbackInfo<void>::Callback weak_callback,
                         WeakCallbackType type);
    static void MakeWeak(internal::Address** location_addr);
    static void* ClearWeak(internal::Address* location);
    static void SetFinalizationCallbackTraced(
        internal::Address* location, void* parameter,
        WeakCallbackInfo<void>::Callback callback);
    static void AnnotateStrongRetainer(internal::Address* location,
                                       const char* label);
    static Value* Eternalize(Isolate* isolate, Value* handle);
  
    template <class K, class V, class T>
    friend class PersistentValueMapBase;
  
    static void FromJustIsNothing();
    static void ToLocalEmpty();
    static void InternalFieldOutOfBounds(int index);
    template <class T>
    friend class Global;
    template <class T> friend class Local;
    template <class T>
    friend class MaybeLocal;
    template <class T>
    friend class Maybe;
    template <class T>
    friend class TracedGlobal;
    template <class T>
    friend class WeakCallbackInfo;
    template <class T> friend class Eternal;
    template <class T> friend class PersistentBase;
    template <class T, class M> friend class Persistent;
    friend class Context;
  };
  
  /**
   * Helper class to create a snapshot data blob.
   */
  class V8_EXPORT SnapshotCreator {
   public:
    enum class FunctionCodeHandling { kClear, kKeep };
  
    /**
     * Initialize and enter an isolate, and set it up for serialization.
     * The isolate is either created from scratch or from an existing snapshot.
     * The caller keeps ownership of the argument snapshot.
     * \param existing_blob existing snapshot from which to create this one.
     * \param external_references a null-terminated array of external references
     *        that must be equivalent to CreateParams::external_references.
     */
    SnapshotCreator(Isolate* isolate,
                    const intptr_t* external_references = nullptr,
                    StartupData* existing_blob = nullptr);
  
    /**
     * Create and enter an isolate, and set it up for serialization.
     * The isolate is either created from scratch or from an existing snapshot.
     * The caller keeps ownership of the argument snapshot.
     * \param existing_blob existing snapshot from which to create this one.
     * \param external_references a null-terminated array of external references
     *        that must be equivalent to CreateParams::external_references.
     */
    SnapshotCreator(const intptr_t* external_references = nullptr,
                    StartupData* existing_blob = nullptr);
  
    ~SnapshotCreator();
  
    /**
     * \returns the isolate prepared by the snapshot creator.
     */
    Isolate* GetIsolate();
  
    /**
     * Set the default context to be included in the snapshot blob.
     * The snapshot will not contain the global proxy, and we expect one or a
     * global object template to create one, to be provided upon deserialization.
     *
     * \param callback optional callback to serialize internal fields.
     */
    void SetDefaultContext(Local<Context> context,
                           SerializeInternalFieldsCallback callback =
                               SerializeInternalFieldsCallback());
  
    /**
     * Add additional context to be included in the snapshot blob.
     * The snapshot will include the global proxy.
     *
     * \param callback optional callback to serialize internal fields.
     *
     * \returns the index of the context in the snapshot blob.
     */
    size_t AddContext(Local<Context> context,
                      SerializeInternalFieldsCallback callback =
                          SerializeInternalFieldsCallback());
  
    /**
     * Add a template to be included in the snapshot blob.
     * \returns the index of the template in the snapshot blob.
     */
    size_t AddTemplate(Local<Template> template_obj);
  
    /**
     * Attach arbitrary V8::Data to the context snapshot, which can be retrieved
     * via Context::GetDataFromSnapshot after deserialization. This data does not
     * survive when a new snapshot is created from an existing snapshot.
     * \returns the index for retrieval.
     */
    template <class T>
    V8_INLINE size_t AddData(Local<Context> context, Local<T> object);
  
    /**
     * Attach arbitrary V8::Data to the isolate snapshot, which can be retrieved
     * via Isolate::GetDataFromSnapshot after deserialization. This data does not
     * survive when a new snapshot is created from an existing snapshot.
     * \returns the index for retrieval.
     */
    template <class T>
    V8_INLINE size_t AddData(Local<T> object);
  
    /**
     * Created a snapshot data blob.
     * This must not be called from within a handle scope.
     * \param function_code_handling whether to include compiled function code
     *        in the snapshot.
     * \returns { nullptr, 0 } on failure, and a startup snapshot on success. The
     *        caller acquires ownership of the data array in the return value.
     */
    StartupData CreateBlob(FunctionCodeHandling function_code_handling);
  
    // Disallow copying and assigning.
    SnapshotCreator(const SnapshotCreator&) = delete;
    void operator=(const SnapshotCreator&) = delete;
  
   private:
    size_t AddData(Local<Context> context, internal::Address object);
    size_t AddData(internal::Address object);
  
    void* data_;
  };
  
  /**
   * A simple Maybe type, representing an object which may or may not have a
   * value, see https://hackage.haskell.org/package/base/docs/Data-Maybe.html.
   *
   * If an API method returns a Maybe<>, the API method can potentially fail
   * either because an exception is thrown, or because an exception is pending,
   * e.g. because a previous API call threw an exception that hasn't been caught
   * yet, or because a TerminateExecution exception was thrown. In that case, a
   * "Nothing" value is returned.
   */
  template <class T>
  class Maybe {
   public:
    V8_INLINE bool IsNothing() const { return !has_value_; }
    V8_INLINE bool IsJust() const { return has_value_; }
  
    /**
     * An alias for |FromJust|. Will crash if the Maybe<> is nothing.
     */
    V8_INLINE T ToChecked() const { return FromJust(); }
  
    /**
     * Short-hand for ToChecked(), which doesn't return a value. To be used, where
     * the actual value of the Maybe is not needed like Object::Set.
     */
    V8_INLINE void Check() const {
      if (V8_UNLIKELY(!IsJust())) V8::FromJustIsNothing();
    }
  
    /**
     * Converts this Maybe<> to a value of type T. If this Maybe<> is
     * nothing (empty), |false| is returned and |out| is left untouched.
     */
    V8_WARN_UNUSED_RESULT V8_INLINE bool To(T* out) const {
      if (V8_LIKELY(IsJust())) *out = value_;
      return IsJust();
    }
  
    /**
     * Converts this Maybe<> to a value of type T. If this Maybe<> is
     * nothing (empty), V8 will crash the process.
     */
    V8_INLINE T FromJust() const {
      if (V8_UNLIKELY(!IsJust())) V8::FromJustIsNothing();
      return value_;
    }
  
    /**
     * Converts this Maybe<> to a value of type T, using a default value if this
     * Maybe<> is nothing (empty).
     */
    V8_INLINE T FromMaybe(const T& default_value) const {
      return has_value_ ? value_ : default_value;
    }
  
    V8_INLINE bool operator==(const Maybe& other) const {
      return (IsJust() == other.IsJust()) &&
             (!IsJust() || FromJust() == other.FromJust());
    }
  
    V8_INLINE bool operator!=(const Maybe& other) const {
      return !operator==(other);
    }
  
   private:
    Maybe() : has_value_(false) {}
    explicit Maybe(const T& t) : has_value_(true), value_(t) {}
  
    bool has_value_;
    T value_;
  
    template <class U>
    friend Maybe<U> Nothing();
    template <class U>
    friend Maybe<U> Just(const U& u);
  };
  
  template <class T>
  inline Maybe<T> Nothing() {
    return Maybe<T>();
  }
  
  template <class T>
  inline Maybe<T> Just(const T& t) {
    return Maybe<T>(t);
  }
  
  // A template specialization of Maybe<T> for the case of T = void.
  template <>
  class Maybe<void> {
   public:
    V8_INLINE bool IsNothing() const { return !is_valid_; }
    V8_INLINE bool IsJust() const { return is_valid_; }
  
    V8_INLINE bool operator==(const Maybe& other) const {
      return IsJust() == other.IsJust();
    }
  
    V8_INLINE bool operator!=(const Maybe& other) const {
      return !operator==(other);
    }
  
   private:
    struct JustTag {};
  
    Maybe() : is_valid_(false) {}
    explicit Maybe(JustTag) : is_valid_(true) {}
  
    bool is_valid_;
  
    template <class U>
    friend Maybe<U> Nothing();
    friend Maybe<void> JustVoid();
  };
  
  inline Maybe<void> JustVoid() { return Maybe<void>(Maybe<void>::JustTag()); }
  
  /**
   * An external exception handler.
   */
  class V8_EXPORT TryCatch {
   public:
    /**
     * Creates a new try/catch block and registers it with v8.  Note that
     * all TryCatch blocks should be stack allocated because the memory
     * location itself is compared against JavaScript try/catch blocks.
     */
    explicit TryCatch(Isolate* isolate);
  
    /**
     * Unregisters and deletes this try/catch block.
     */
    ~TryCatch();
  
    /**
     * Returns true if an exception has been caught by this try/catch block.
     */
    bool HasCaught() const;
  
    /**
     * For certain types of exceptions, it makes no sense to continue execution.
     *
     * If CanContinue returns false, the correct action is to perform any C++
     * cleanup needed and then return.  If CanContinue returns false and
     * HasTerminated returns true, it is possible to call
     * CancelTerminateExecution in order to continue calling into the engine.
     */
    bool CanContinue() const;
  
    /**
     * Returns true if an exception has been caught due to script execution
     * being terminated.
     *
     * There is no JavaScript representation of an execution termination
     * exception.  Such exceptions are thrown when the TerminateExecution
     * methods are called to terminate a long-running script.
     *
     * If such an exception has been thrown, HasTerminated will return true,
     * indicating that it is possible to call CancelTerminateExecution in order
     * to continue calling into the engine.
     */
    bool HasTerminated() const;
  
    /**
     * Throws the exception caught by this TryCatch in a way that avoids
     * it being caught again by this same TryCatch.  As with ThrowException
     * it is illegal to execute any JavaScript operations after calling
     * ReThrow; the caller must return immediately to where the exception
     * is caught.
     */
    Local<Value> ReThrow();
  
    /**
     * Returns the exception caught by this try/catch block.  If no exception has
     * been caught an empty handle is returned.
     *
     * The returned handle is valid until this TryCatch block has been destroyed.
     */
    Local<Value> Exception() const;
  
    /**
     * Returns the .stack property of the thrown object.  If no .stack
     * property is present an empty handle is returned.
     */
    V8_WARN_UNUSED_RESULT MaybeLocal<Value> StackTrace(
        Local<Context> context) const;
  
    /**
     * Returns the message associated with this exception.  If there is
     * no message associated an empty handle is returned.
     *
     * The returned handle is valid until this TryCatch block has been
     * destroyed.
     */
    Local<v8::Message> Message() const;
  
    /**
     * Clears any exceptions that may have been caught by this try/catch block.
     * After this method has been called, HasCaught() will return false. Cancels
     * the scheduled exception if it is caught and ReThrow() is not called before.
     *
     * It is not necessary to clear a try/catch block before using it again; if
     * another exception is thrown the previously caught exception will just be
     * overwritten.  However, it is often a good idea since it makes it easier
     * to determine which operation threw a given exception.
     */
    void Reset();
  
    /**
     * Set verbosity of the external exception handler.
     *
     * By default, exceptions that are caught by an external exception
     * handler are not reported.  Call SetVerbose with true on an
     * external exception handler to have exceptions caught by the
     * handler reported as if they were not caught.
     */
    void SetVerbose(bool value);
  
    /**
     * Returns true if verbosity is enabled.
     */
    bool IsVerbose() const;
  
    /**
     * Set whether or not this TryCatch should capture a Message object
     * which holds source information about where the exception
     * occurred.  True by default.
     */
    void SetCaptureMessage(bool value);
  
    /**
     * There are cases when the raw address of C++ TryCatch object cannot be
     * used for comparisons with addresses into the JS stack. The cases are:
     * 1) ARM, ARM64 and MIPS simulators which have separate JS stack.
     * 2) Address sanitizer allocates local C++ object in the heap when
     *    UseAfterReturn mode is enabled.
     * This method returns address that can be used for comparisons with
     * addresses into the JS stack. When neither simulator nor ASAN's
     * UseAfterReturn is enabled, then the address returned will be the address
     * of the C++ try catch handler itself.
     */
    static void* JSStackComparableAddress(TryCatch* handler) {
      if (handler == nullptr) return nullptr;
      return handler->js_stack_comparable_address_;
    }
  
    TryCatch(const TryCatch&) = delete;
    void operator=(const TryCatch&) = delete;
  
   private:
    // Declaring operator new and delete as deleted is not spec compliant.
    // Therefore declare them private instead to disable dynamic alloc
    void* operator new(size_t size);
    void* operator new[](size_t size);
    void operator delete(void*, size_t);
    void operator delete[](void*, size_t);
  
    void ResetInternal();
  
    internal::Isolate* isolate_;
    TryCatch* next_;
    void* exception_;
    void* message_obj_;
    void* js_stack_comparable_address_;
    bool is_verbose_ : 1;
    bool can_continue_ : 1;
    bool capture_message_ : 1;
    bool rethrow_ : 1;
    bool has_terminated_ : 1;
  
    friend class internal::Isolate;
  };
  
  
  // --- Context ---
  
  
  /**
   * A container for extension names.
   */
  class V8_EXPORT ExtensionConfiguration {
   public:
    ExtensionConfiguration() : name_count_(0), names_(nullptr) {}
    ExtensionConfiguration(int name_count, const char* names[])
        : name_count_(name_count), names_(names) { }
  
    const char** begin() const { return &names_[0]; }
    const char** end()  const { return &names_[name_count_]; }
  
   private:
    const int name_count_;
    const char** names_;
  };
  
  /**
   * A sandboxed execution context with its own set of built-in objects
   * and functions.
   */
  class V8_EXPORT Context {
   public:
    /**
     * Returns the global proxy object.
     *
     * Global proxy object is a thin wrapper whose prototype points to actual
     * context's global object with the properties like Object, etc. This is done
     * that way for security reasons (for more details see
     * https://wiki.mozilla.org/Gecko:SplitWindow).
     *
     * Please note that changes to global proxy object prototype most probably
     * would break VM---v8 expects only global object as a prototype of global
     * proxy object.
     */
    Local<Object> Global();
  
    /**
     * Detaches the global object from its context before
     * the global object can be reused to create a new context.
     */
    void DetachGlobal();
  
    /**
     * Creates a new context and returns a handle to the newly allocated
     * context.
     *
     * \param isolate The isolate in which to create the context.
     *
     * \param extensions An optional extension configuration containing
     * the extensions to be installed in the newly created context.
     *
     * \param global_template An optional object template from which the
     * global object for the newly created context will be created.
     *
     * \param global_object An optional global object to be reused for
     * the newly created context. This global object must have been
     * created by a previous call to Context::New with the same global
     * template. The state of the global object will be completely reset
     * and only object identify will remain.
     */
    static Local<Context> New(
        Isolate* isolate, ExtensionConfiguration* extensions = nullptr,
        MaybeLocal<ObjectTemplate> global_template = MaybeLocal<ObjectTemplate>(),
        MaybeLocal<Value> global_object = MaybeLocal<Value>(),
        DeserializeInternalFieldsCallback internal_fields_deserializer =
            DeserializeInternalFieldsCallback(),
        MicrotaskQueue* microtask_queue = nullptr);
  
    /**
     * Create a new context from a (non-default) context snapshot. There
     * is no way to provide a global object template since we do not create
     * a new global object from template, but we can reuse a global object.
     *
     * \param isolate See v8::Context::New.
     *
     * \param context_snapshot_index The index of the context snapshot to
     * deserialize from. Use v8::Context::New for the default snapshot.
     *
     * \param embedder_fields_deserializer Optional callback to deserialize
     * internal fields. It should match the SerializeInternalFieldCallback used
     * to serialize.
     *
     * \param extensions See v8::Context::New.
     *
     * \param global_object See v8::Context::New.
     */
    static MaybeLocal<Context> FromSnapshot(
        Isolate* isolate, size_t context_snapshot_index,
        DeserializeInternalFieldsCallback embedder_fields_deserializer =
            DeserializeInternalFieldsCallback(),
        ExtensionConfiguration* extensions = nullptr,
        MaybeLocal<Value> global_object = MaybeLocal<Value>(),
        MicrotaskQueue* microtask_queue = nullptr);
  
    /**
     * Returns an global object that isn't backed by an actual context.
     *
     * The global template needs to have access checks with handlers installed.
     * If an existing global object is passed in, the global object is detached
     * from its context.
     *
     * Note that this is different from a detached context where all accesses to
     * the global proxy will fail. Instead, the access check handlers are invoked.
     *
     * It is also not possible to detach an object returned by this method.
     * Instead, the access check handlers need to return nothing to achieve the
     * same effect.
     *
     * It is possible, however, to create a new context from the global object
     * returned by this method.
     */
    static MaybeLocal<Object> NewRemoteContext(
        Isolate* isolate, Local<ObjectTemplate> global_template,
        MaybeLocal<Value> global_object = MaybeLocal<Value>());
  
    /**
     * Sets the security token for the context.  To access an object in
     * another context, the security tokens must match.
     */
    void SetSecurityToken(Local<Value> token);
  
    /** Restores the security token to the default value. */
    void UseDefaultSecurityToken();
  
    /** Returns the security token of this context.*/
    Local<Value> GetSecurityToken();
  
    /**
     * Enter this context.  After entering a context, all code compiled
     * and run is compiled and run in this context.  If another context
     * is already entered, this old context is saved so it can be
     * restored when the new context is exited.
     */
    void Enter();
  
    /**
     * Exit this context.  Exiting the current context restores the
     * context that was in place when entering the current context.
     */
    void Exit();
  
    /** Returns an isolate associated with a current context. */
    Isolate* GetIsolate();
  
    /**
     * The field at kDebugIdIndex used to be reserved for the inspector.
     * It now serves no purpose.
     */
    enum EmbedderDataFields { kDebugIdIndex = 0 };
  
    /**
     * Return the number of fields allocated for embedder data.
     */
    uint32_t GetNumberOfEmbedderDataFields();
  
    /**
     * Gets the embedder data with the given index, which must have been set by a
     * previous call to SetEmbedderData with the same index.
     */
    V8_INLINE Local<Value> GetEmbedderData(int index);
  
    /**
     * Gets the binding object used by V8 extras. Extra natives get a reference
     * to this object and can use it to "export" functionality by adding
     * properties. Extra natives can also "import" functionality by accessing
     * properties added by the embedder using the V8 API.
     */
    Local<Object> GetExtrasBindingObject();
  
    /**
     * Sets the embedder data with the given index, growing the data as
     * needed. Note that index 0 currently has a special meaning for Chrome's
     * debugger.
     */
    void SetEmbedderData(int index, Local<Value> value);
  
    /**
     * Gets a 2-byte-aligned native pointer from the embedder data with the given
     * index, which must have been set by a previous call to
     * SetAlignedPointerInEmbedderData with the same index. Note that index 0
     * currently has a special meaning for Chrome's debugger.
     */
    V8_INLINE void* GetAlignedPointerFromEmbedderData(int index);
  
    /**
     * Sets a 2-byte-aligned native pointer in the embedder data with the given
     * index, growing the data as needed. Note that index 0 currently has a
     * special meaning for Chrome's debugger.
     */
    void SetAlignedPointerInEmbedderData(int index, void* value);
  
    /**
     * Control whether code generation from strings is allowed. Calling
     * this method with false will disable 'eval' and the 'Function'
     * constructor for code running in this context. If 'eval' or the
     * 'Function' constructor are used an exception will be thrown.
     *
     * If code generation from strings is not allowed the
     * V8::AllowCodeGenerationFromStrings callback will be invoked if
     * set before blocking the call to 'eval' or the 'Function'
     * constructor. If that callback returns true, the call will be
     * allowed, otherwise an exception will be thrown. If no callback is
     * set an exception will be thrown.
     */
    void AllowCodeGenerationFromStrings(bool allow);
  
    /**
     * Returns true if code generation from strings is allowed for the context.
     * For more details see AllowCodeGenerationFromStrings(bool) documentation.
     */
    bool IsCodeGenerationFromStringsAllowed();
  
    /**
     * Sets the error description for the exception that is thrown when
     * code generation from strings is not allowed and 'eval' or the 'Function'
     * constructor are called.
     */
    void SetErrorMessageForCodeGenerationFromStrings(Local<String> message);
  
    /**
     * Return data that was previously attached to the context snapshot via
     * SnapshotCreator, and removes the reference to it.
     * Repeated call with the same index returns an empty MaybeLocal.
     */
    template <class T>
    V8_INLINE MaybeLocal<T> GetDataFromSnapshotOnce(size_t index);
  
    /**
     * If callback is set, abort any attempt to execute JavaScript in this
     * context, call the specified callback, and throw an exception.
     * To unset abort, pass nullptr as callback.
     */
    typedef void (*AbortScriptExecutionCallback)(Isolate* isolate,
                                                 Local<Context> context);
    void SetAbortScriptExecution(AbortScriptExecutionCallback callback);
  
    /**
     * Stack-allocated class which sets the execution context for all
     * operations executed within a local scope.
     */
    class Scope {
     public:
      explicit V8_INLINE Scope(Local<Context> context) : context_(context) {
        context_->Enter();
      }
      V8_INLINE ~Scope() { context_->Exit(); }
  
     private:
      Local<Context> context_;
    };
  
    /**
     * Stack-allocated class to support the backup incumbent settings object
     * stack.
     * https://html.spec.whatwg.org/multipage/webappapis.html#backup-incumbent-settings-object-stack
     */
    class V8_EXPORT BackupIncumbentScope final {
     public:
      /**
       * |backup_incumbent_context| is pushed onto the backup incumbent settings
       * object stack.
       */
      explicit BackupIncumbentScope(Local<Context> backup_incumbent_context);
      ~BackupIncumbentScope();
  
      /**
       * Returns address that is comparable with JS stack address.  Note that JS
       * stack may be allocated separately from the native stack.  See also
       * |TryCatch::JSStackComparableAddress| for details.
       */
      uintptr_t JSStackComparableAddress() const {
        return js_stack_comparable_address_;
      }
  
     private:
      friend class internal::Isolate;
  
      Local<Context> backup_incumbent_context_;
      uintptr_t js_stack_comparable_address_ = 0;
      const BackupIncumbentScope* prev_ = nullptr;
    };
  
   private:
    friend class Value;
    friend class Script;
    friend class Object;
    friend class Function;
  
    internal::Address* GetDataFromSnapshotOnce(size_t index);
    Local<Value> SlowGetEmbedderData(int index);
    void* SlowGetAlignedPointerFromEmbedderData(int index);
  };
  
  
  /**
   * Multiple threads in V8 are allowed, but only one thread at a time is allowed
   * to use any given V8 isolate, see the comments in the Isolate class. The
   * definition of 'using a V8 isolate' includes accessing handles or holding onto
   * object pointers obtained from V8 handles while in the particular V8 isolate.
   * It is up to the user of V8 to ensure, perhaps with locking, that this
   * constraint is not violated. In addition to any other synchronization
   * mechanism that may be used, the v8::Locker and v8::Unlocker classes must be
   * used to signal thread switches to V8.
   *
   * v8::Locker is a scoped lock object. While it's active, i.e. between its
   * construction and destruction, the current thread is allowed to use the locked
   * isolate. V8 guarantees that an isolate can be locked by at most one thread at
   * any time. In other words, the scope of a v8::Locker is a critical section.
   *
   * Sample usage:
  * \code
   * ...
   * {
   *   v8::Locker locker(isolate);
   *   v8::Isolate::Scope isolate_scope(isolate);
   *   ...
   *   // Code using V8 and isolate goes here.
   *   ...
   * } // Destructor called here
   * \endcode
   *
   * If you wish to stop using V8 in a thread A you can do this either by
   * destroying the v8::Locker object as above or by constructing a v8::Unlocker
   * object:
   *
   * \code
   * {
   *   isolate->Exit();
   *   v8::Unlocker unlocker(isolate);
   *   ...
   *   // Code not using V8 goes here while V8 can run in another thread.
   *   ...
   * } // Destructor called here.
   * isolate->Enter();
   * \endcode
   *
   * The Unlocker object is intended for use in a long-running callback from V8,
   * where you want to release the V8 lock for other threads to use.
   *
   * The v8::Locker is a recursive lock, i.e. you can lock more than once in a
   * given thread. This can be useful if you have code that can be called either
   * from code that holds the lock or from code that does not. The Unlocker is
   * not recursive so you can not have several Unlockers on the stack at once, and
   * you can not use an Unlocker in a thread that is not inside a Locker's scope.
   *
   * An unlocker will unlock several lockers if it has to and reinstate the
   * correct depth of locking on its destruction, e.g.:
   *
   * \code
   * // V8 not locked.
   * {
   *   v8::Locker locker(isolate);
   *   Isolate::Scope isolate_scope(isolate);
   *   // V8 locked.
   *   {
   *     v8::Locker another_locker(isolate);
   *     // V8 still locked (2 levels).
   *     {
   *       isolate->Exit();
   *       v8::Unlocker unlocker(isolate);
   *       // V8 not locked.
   *     }
   *     isolate->Enter();
   *     // V8 locked again (2 levels).
   *   }
   *   // V8 still locked (1 level).
   * }
   * // V8 Now no longer locked.
   * \endcode
   */
  class V8_EXPORT Unlocker {
   public:
    /**
     * Initialize Unlocker for a given Isolate.
     */
    V8_INLINE explicit Unlocker(Isolate* isolate) { Initialize(isolate); }
  
    ~Unlocker();
   private:
    void Initialize(Isolate* isolate);
  
    internal::Isolate* isolate_;
  };
  
  
  class V8_EXPORT Locker {
   public:
    /**
     * Initialize Locker for a given Isolate.
     */
    V8_INLINE explicit Locker(Isolate* isolate) { Initialize(isolate); }
  
    ~Locker();
  
    /**
     * Returns whether or not the locker for a given isolate, is locked by the
     * current thread.
     */
    static bool IsLocked(Isolate* isolate);
  
    /**
     * Returns whether v8::Locker is being used by this V8 instance.
     */
    static bool IsActive();
  
    // Disallow copying and assigning.
    Locker(const Locker&) = delete;
    void operator=(const Locker&) = delete;
  
   private:
    void Initialize(Isolate* isolate);
  
    bool has_lock_;
    bool top_level_;
    internal::Isolate* isolate_;
  };
  
  /**
   * Various helpers for skipping over V8 frames in a given stack.
   *
   * The unwinder API is only supported on the x64 architecture.
   */
  class V8_EXPORT Unwinder {
   public:
    /**
     * Attempt to unwind the stack to the most recent C++ frame. This function is
     * signal-safe and does not access any V8 state and thus doesn't require an
     * Isolate.
     *
     * The unwinder needs to know the location of the JS Entry Stub (a piece of
     * code that is run when C++ code calls into generated JS code). This is used
     * for edge cases where the current frame is being constructed or torn down
     * when the stack sample occurs.
     *
     * The unwinder also needs the virtual memory range of all possible V8 code
     * objects. There are two ranges required - the heap code range and the range
     * for code embedded in the binary. The V8 API provides all required inputs
     * via an UnwindState object through the Isolate::GetUnwindState() API. These
     * values will not change after Isolate initialization, so the same
     * |unwind_state| can be used for multiple calls.
     *
     * \param unwind_state Input state for the Isolate that the stack comes from.
     * \param register_state The current registers. This is an in-out param that
     * will be overwritten with the register values after unwinding, on success.
     * \param stack_base The resulting stack pointer and frame pointer values are
     * bounds-checked against the stack_base and the original stack pointer value
     * to ensure that they are valid locations in the given stack. If these values
     * or any intermediate frame pointer values used during unwinding are ever out
     * of these bounds, unwinding will fail.
     *
     * \return True on success.
     */
    static bool TryUnwindV8Frames(const UnwindState& unwind_state,
                                  RegisterState* register_state,
                                  const void* stack_base);
  
    /**
     * Whether the PC is within the V8 code range represented by code_range or
     * embedded_code_range in |unwind_state|.
     *
     * If this returns false, then calling UnwindV8Frames() with the same PC
     * and unwind_state will always fail. If it returns true, then unwinding may
     * (but not necessarily) be successful.
     */
    static bool PCIsInV8(const UnwindState& unwind_state, void* pc);
  };
  
  // --- Implementation ---
  
  template <class T>
  Local<T> Local<T>::New(Isolate* isolate, Local<T> that) {
    return New(isolate, that.val_);
  }
  
  template <class T>
  Local<T> Local<T>::New(Isolate* isolate, const PersistentBase<T>& that) {
    return New(isolate, that.val_);
  }
  
  template <class T>
  Local<T> Local<T>::New(Isolate* isolate, const TracedGlobal<T>& that) {
    return New(isolate, that.val_);
  }
  
  template <class T>
  Local<T> Local<T>::New(Isolate* isolate, T* that) {
    if (that == nullptr) return Local<T>();
    T* that_ptr = that;
    internal::Address* p = reinterpret_cast<internal::Address*>(that_ptr);
    return Local<T>(reinterpret_cast<T*>(HandleScope::CreateHandle(
        reinterpret_cast<internal::Isolate*>(isolate), *p)));
  }
  
  
  template<class T>
  template<class S>
  void Eternal<T>::Set(Isolate* isolate, Local<S> handle) {
    TYPE_CHECK(T, S);
    val_ = reinterpret_cast<T*>(
        V8::Eternalize(isolate, reinterpret_cast<Value*>(*handle)));
  }
  
  template <class T>
  Local<T> Eternal<T>::Get(Isolate* isolate) const {
    // The eternal handle will never go away, so as with the roots, we don't even
    // need to open a handle.
    return Local<T>(val_);
  }
  
  
  template <class T>
  Local<T> MaybeLocal<T>::ToLocalChecked() {
    if (V8_UNLIKELY(val_ == nullptr)) V8::ToLocalEmpty();
    return Local<T>(val_);
  }
  
  
  template <class T>
  void* WeakCallbackInfo<T>::GetInternalField(int index) const {
  #ifdef V8_ENABLE_CHECKS
    if (index < 0 || index >= kEmbedderFieldsInWeakCallback) {
      V8::InternalFieldOutOfBounds(index);
    }
  #endif
    return embedder_fields_[index];
  }
  
  
  template <class T>
  T* PersistentBase<T>::New(Isolate* isolate, T* that) {
    if (that == nullptr) return nullptr;
    internal::Address* p = reinterpret_cast<internal::Address*>(that);
    return reinterpret_cast<T*>(
        V8::GlobalizeReference(reinterpret_cast<internal::Isolate*>(isolate),
                               p));
  }
  
  
  template <class T, class M>
  template <class S, class M2>
  void Persistent<T, M>::Copy(const Persistent<S, M2>& that) {
    TYPE_CHECK(T, S);
    this->Reset();
    if (that.IsEmpty()) return;
    internal::Address* p = reinterpret_cast<internal::Address*>(that.val_);
    this->val_ = reinterpret_cast<T*>(V8::CopyGlobalReference(p));
    M::Copy(that, this);
  }
  
  template <class T>
  bool PersistentBase<T>::IsWeak() const {
    typedef internal::Internals I;
    if (this->IsEmpty()) return false;
    return I::GetNodeState(reinterpret_cast<internal::Address*>(this->val_)) ==
           I::kNodeStateIsWeakValue;
  }
  
  
  template <class T>
  void PersistentBase<T>::Reset() {
    if (this->IsEmpty()) return;
    V8::DisposeGlobal(reinterpret_cast<internal::Address*>(this->val_));
    val_ = nullptr;
  }
  
  
  template <class T>
  template <class S>
  void PersistentBase<T>::Reset(Isolate* isolate, const Local<S>& other) {
    TYPE_CHECK(T, S);
    Reset();
    if (other.IsEmpty()) return;
    this->val_ = New(isolate, other.val_);
  }
  
  
  template <class T>
  template <class S>
  void PersistentBase<T>::Reset(Isolate* isolate,
                                const PersistentBase<S>& other) {
    TYPE_CHECK(T, S);
    Reset();
    if (other.IsEmpty()) return;
    this->val_ = New(isolate, other.val_);
  }
  
  
  template <class T>
  template <typename P>
  V8_INLINE void PersistentBase<T>::SetWeak(
      P* parameter, typename WeakCallbackInfo<P>::Callback callback,
      WeakCallbackType type) {
    typedef typename WeakCallbackInfo<void>::Callback Callback;
    V8::MakeWeak(reinterpret_cast<internal::Address*>(this->val_), parameter,
                 reinterpret_cast<Callback>(callback), type);
  }
  
  template <class T>
  void PersistentBase<T>::SetWeak() {
    V8::MakeWeak(reinterpret_cast<internal::Address**>(&this->val_));
  }
  
  template <class T>
  template <typename P>
  P* PersistentBase<T>::ClearWeak() {
    return reinterpret_cast<P*>(
        V8::ClearWeak(reinterpret_cast<internal::Address*>(this->val_)));
  }
  
  template <class T>
  void PersistentBase<T>::AnnotateStrongRetainer(const char* label) {
    V8::AnnotateStrongRetainer(reinterpret_cast<internal::Address*>(this->val_),
                               label);
  }
  
  template <class T>
  void PersistentBase<T>::SetWrapperClassId(uint16_t class_id) {
    typedef internal::Internals I;
    if (this->IsEmpty()) return;
    internal::Address* obj = reinterpret_cast<internal::Address*>(this->val_);
    uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + I::kNodeClassIdOffset;
    *reinterpret_cast<uint16_t*>(addr) = class_id;
  }
  
  
  template <class T>
  uint16_t PersistentBase<T>::WrapperClassId() const {
    typedef internal::Internals I;
    if (this->IsEmpty()) return 0;
    internal::Address* obj = reinterpret_cast<internal::Address*>(this->val_);
    uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + I::kNodeClassIdOffset;
    return *reinterpret_cast<uint16_t*>(addr);
  }
  
  template <class T>
  Global<T>::Global(Global&& other) : PersistentBase<T>(other.val_) {
    if (other.val_ != nullptr) {
      V8::MoveGlobalReference(reinterpret_cast<internal::Address**>(&other.val_),
                              reinterpret_cast<internal::Address**>(&this->val_));
      other.val_ = nullptr;
    }
  }
  
  template <class T>
  template <class S>
  Global<T>& Global<T>::operator=(Global<S>&& rhs) {
    TYPE_CHECK(T, S);
    if (this != &rhs) {
      this->Reset();
      if (rhs.val_ != nullptr) {
        this->val_ = rhs.val_;
        V8::MoveGlobalReference(
            reinterpret_cast<internal::Address**>(&rhs.val_),
            reinterpret_cast<internal::Address**>(&this->val_));
        rhs.val_ = nullptr;
      }
    }
    return *this;
  }
  
  template <class T>
  T* TracedGlobal<T>::New(Isolate* isolate, T* that, T** slot) {
    if (that == nullptr) return nullptr;
    internal::Address* p = reinterpret_cast<internal::Address*>(that);
    return reinterpret_cast<T*>(V8::GlobalizeTracedReference(
        reinterpret_cast<internal::Isolate*>(isolate), p,
        reinterpret_cast<internal::Address*>(slot)));
  }
  
  template <class T>
  void TracedGlobal<T>::Reset() {
    if (IsEmpty()) return;
    V8::DisposeTracedGlobal(reinterpret_cast<internal::Address*>(val_));
    val_ = nullptr;
  }
  
  template <class T>
  template <class S>
  void TracedGlobal<T>::Reset(Isolate* isolate, const Local<S>& other) {
    TYPE_CHECK(T, S);
    Reset();
    if (other.IsEmpty()) return;
    this->val_ = New(isolate, other.val_, &val_);
  }
  
  template <class T>
  TracedGlobal<T>::TracedGlobal(TracedGlobal&& other) : val_(other.val_) {
    if (other.val_ != nullptr) {
      V8::MoveTracedGlobalReference(
          reinterpret_cast<internal::Address**>(&other.val_),
          reinterpret_cast<internal::Address**>(&this->val_));
      other.val_ = nullptr;
    }
  }
  
  template <class T>
  template <class S>
  TracedGlobal<T>& TracedGlobal<T>::operator=(TracedGlobal<S>&& rhs) {
    TYPE_CHECK(T, S);
    if (this != &rhs) {
      this->Reset();
      if (rhs.val_ != nullptr) {
        this->val_ = rhs.val_;
        V8::MoveTracedGlobalReference(
            reinterpret_cast<internal::Address**>(&rhs.val_),
            reinterpret_cast<internal::Address**>(&this->val_));
        rhs.val_ = nullptr;
      }
    }
    return *this;
  }
  
  template <class T>
  void TracedGlobal<T>::SetWrapperClassId(uint16_t class_id) {
    typedef internal::Internals I;
    if (IsEmpty()) return;
    internal::Address* obj = reinterpret_cast<internal::Address*>(this->val_);
    uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + I::kNodeClassIdOffset;
    *reinterpret_cast<uint16_t*>(addr) = class_id;
  }
  
  template <class T>
  uint16_t TracedGlobal<T>::WrapperClassId() const {
    typedef internal::Internals I;
    if (IsEmpty()) return 0;
    internal::Address* obj = reinterpret_cast<internal::Address*>(this->val_);
    uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + I::kNodeClassIdOffset;
    return *reinterpret_cast<uint16_t*>(addr);
  }
  
  template <class T>
  void TracedGlobal<T>::SetFinalizationCallback(
      void* parameter, typename WeakCallbackInfo<void>::Callback callback) {
    V8::SetFinalizationCallbackTraced(
        reinterpret_cast<internal::Address*>(this->val_), parameter, callback);
  }
  
  template <typename T>
  ReturnValue<T>::ReturnValue(internal::Address* slot) : value_(slot) {}
  
  template <typename T>
  template <typename S>
  void ReturnValue<T>::Set(const Global<S>& handle) {
    TYPE_CHECK(T, S);
    if (V8_UNLIKELY(handle.IsEmpty())) {
      *value_ = GetDefaultValue();
    } else {
      *value_ = *reinterpret_cast<internal::Address*>(*handle);
    }
  }
  
  template <typename T>
  template <typename S>
  void ReturnValue<T>::Set(const TracedGlobal<S>& handle) {
    TYPE_CHECK(T, S);
    if (V8_UNLIKELY(handle.IsEmpty())) {
      *value_ = GetDefaultValue();
    } else {
      *value_ = *reinterpret_cast<internal::Address*>(*handle);
    }
  }
  
  template <typename T>
  template <typename S>
  void ReturnValue<T>::Set(const Local<S> handle) {
    TYPE_CHECK(T, S);
    if (V8_UNLIKELY(handle.IsEmpty())) {
      *value_ = GetDefaultValue();
    } else {
      *value_ = *reinterpret_cast<internal::Address*>(*handle);
    }
  }
  
  template<typename T>
  void ReturnValue<T>::Set(double i) {
    TYPE_CHECK(T, Number);
    Set(Number::New(GetIsolate(), i));
  }
  
  template<typename T>
  void ReturnValue<T>::Set(int32_t i) {
    TYPE_CHECK(T, Integer);
    typedef internal::Internals I;
    if (V8_LIKELY(I::IsValidSmi(i))) {
      *value_ = I::IntToSmi(i);
      return;
    }
    Set(Integer::New(GetIsolate(), i));
  }
  
  template<typename T>
  void ReturnValue<T>::Set(uint32_t i) {
    TYPE_CHECK(T, Integer);
    // Can't simply use INT32_MAX here for whatever reason.
    bool fits_into_int32_t = (i & (1U << 31)) == 0;
    if (V8_LIKELY(fits_into_int32_t)) {
      Set(static_cast<int32_t>(i));
      return;
    }
    Set(Integer::NewFromUnsigned(GetIsolate(), i));
  }
  
  template<typename T>
  void ReturnValue<T>::Set(bool value) {
    TYPE_CHECK(T, Boolean);
    typedef internal::Internals I;
    int root_index;
    if (value) {
      root_index = I::kTrueValueRootIndex;
    } else {
      root_index = I::kFalseValueRootIndex;
    }
    *value_ = *I::GetRoot(GetIsolate(), root_index);
  }
  
  template<typename T>
  void ReturnValue<T>::SetNull() {
    TYPE_CHECK(T, Primitive);
    typedef internal::Internals I;
    *value_ = *I::GetRoot(GetIsolate(), I::kNullValueRootIndex);
  }
  
  template<typename T>
  void ReturnValue<T>::SetUndefined() {
    TYPE_CHECK(T, Primitive);
    typedef internal::Internals I;
    *value_ = *I::GetRoot(GetIsolate(), I::kUndefinedValueRootIndex);
  }
  
  template<typename T>
  void ReturnValue<T>::SetEmptyString() {
    TYPE_CHECK(T, String);
    typedef internal::Internals I;
    *value_ = *I::GetRoot(GetIsolate(), I::kEmptyStringRootIndex);
  }
  
  template <typename T>
  Isolate* ReturnValue<T>::GetIsolate() const {
    // Isolate is always the pointer below the default value on the stack.
    return *reinterpret_cast<Isolate**>(&value_[-2]);
  }
  
  template <typename T>
  Local<Value> ReturnValue<T>::Get() const {
    typedef internal::Internals I;
    if (*value_ == *I::GetRoot(GetIsolate(), I::kTheHoleValueRootIndex))
      return Local<Value>(*Undefined(GetIsolate()));
    return Local<Value>::New(GetIsolate(), reinterpret_cast<Value*>(value_));
  }
  
  template <typename T>
  template <typename S>
  void ReturnValue<T>::Set(S* whatever) {
    // Uncompilable to prevent inadvertent misuse.
    TYPE_CHECK(S*, Primitive);
  }
  
  template <typename T>
  internal::Address ReturnValue<T>::GetDefaultValue() {
    // Default value is always the pointer below value_ on the stack.
    return value_[-1];
  }
  
  template <typename T>
  FunctionCallbackInfo<T>::FunctionCallbackInfo(internal::Address* implicit_args,
                                                internal::Address* values,
                                                int length)
      : implicit_args_(implicit_args), values_(values), length_(length) {}
  
  template<typename T>
  Local<Value> FunctionCallbackInfo<T>::operator[](int i) const {
    if (i < 0 || length_ <= i) return Local<Value>(*Undefined(GetIsolate()));
    return Local<Value>(reinterpret_cast<Value*>(values_ - i));
  }
  
  
  template<typename T>
  Local<Object> FunctionCallbackInfo<T>::This() const {
    return Local<Object>(reinterpret_cast<Object*>(values_ + 1));
  }
  
  
  template<typename T>
  Local<Object> FunctionCallbackInfo<T>::Holder() const {
    return Local<Object>(reinterpret_cast<Object*>(
        &implicit_args_[kHolderIndex]));
  }
  
  template <typename T>
  Local<Value> FunctionCallbackInfo<T>::NewTarget() const {
    return Local<Value>(
        reinterpret_cast<Value*>(&implicit_args_[kNewTargetIndex]));
  }
  
  template <typename T>
  Local<Value> FunctionCallbackInfo<T>::Data() const {
    return Local<Value>(reinterpret_cast<Value*>(&implicit_args_[kDataIndex]));
  }
  
  
  template<typename T>
  Isolate* FunctionCallbackInfo<T>::GetIsolate() const {
    return *reinterpret_cast<Isolate**>(&implicit_args_[kIsolateIndex]);
  }
  
  
  template<typename T>
  ReturnValue<T> FunctionCallbackInfo<T>::GetReturnValue() const {
    return ReturnValue<T>(&implicit_args_[kReturnValueIndex]);
  }
  
  
  template<typename T>
  bool FunctionCallbackInfo<T>::IsConstructCall() const {
    return !NewTarget()->IsUndefined();
  }
  
  
  template<typename T>
  int FunctionCallbackInfo<T>::Length() const {
    return length_;
  }
  
  ScriptOrigin::ScriptOrigin(Local<Value> resource_name,
                             Local<Integer> resource_line_offset,
                             Local<Integer> resource_column_offset,
                             Local<Boolean> resource_is_shared_cross_origin,
                             Local<Integer> script_id,
                             Local<Value> source_map_url,
                             Local<Boolean> resource_is_opaque,
                             Local<Boolean> is_wasm, Local<Boolean> is_module,
                             Local<PrimitiveArray> host_defined_options)
      : resource_name_(resource_name),
        resource_line_offset_(resource_line_offset),
        resource_column_offset_(resource_column_offset),
        options_(!resource_is_shared_cross_origin.IsEmpty() &&
                     resource_is_shared_cross_origin->IsTrue(),
                 !resource_is_opaque.IsEmpty() && resource_is_opaque->IsTrue(),
                 !is_wasm.IsEmpty() && is_wasm->IsTrue(),
                 !is_module.IsEmpty() && is_module->IsTrue()),
        script_id_(script_id),
        source_map_url_(source_map_url),
        host_defined_options_(host_defined_options) {}
  
  Local<Value> ScriptOrigin::ResourceName() const { return resource_name_; }
  
  Local<PrimitiveArray> ScriptOrigin::HostDefinedOptions() const {
    return host_defined_options_;
  }
  
  Local<Integer> ScriptOrigin::ResourceLineOffset() const {
    return resource_line_offset_;
  }
  
  
  Local<Integer> ScriptOrigin::ResourceColumnOffset() const {
    return resource_column_offset_;
  }
  
  
  Local<Integer> ScriptOrigin::ScriptID() const { return script_id_; }
  
  
  Local<Value> ScriptOrigin::SourceMapUrl() const { return source_map_url_; }
  
  ScriptCompiler::Source::Source(Local<String> string, const ScriptOrigin& origin,
                                 CachedData* data)
      : source_string(string),
        resource_name(origin.ResourceName()),
        resource_line_offset(origin.ResourceLineOffset()),
        resource_column_offset(origin.ResourceColumnOffset()),
        resource_options(origin.Options()),
        source_map_url(origin.SourceMapUrl()),
        host_defined_options(origin.HostDefinedOptions()),
        cached_data(data) {}
  
  ScriptCompiler::Source::Source(Local<String> string,
                                 CachedData* data)
      : source_string(string), cached_data(data) {}
  
  
  ScriptCompiler::Source::~Source() {
    delete cached_data;
  }
  
  
  const ScriptCompiler::CachedData* ScriptCompiler::Source::GetCachedData()
      const {
    return cached_data;
  }
  
  const ScriptOriginOptions& ScriptCompiler::Source::GetResourceOptions() const {
    return resource_options;
  }
  
  Local<Boolean> Boolean::New(Isolate* isolate, bool value) {
    return value ? True(isolate) : False(isolate);
  }
  
  void Template::Set(Isolate* isolate, const char* name, Local<Data> value) {
    Set(String::NewFromUtf8(isolate, name, NewStringType::kInternalized)
            .ToLocalChecked(),
        value);
  }
  
  FunctionTemplate* FunctionTemplate::Cast(Data* data) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(data);
  #endif
    return reinterpret_cast<FunctionTemplate*>(data);
  }
  
  ObjectTemplate* ObjectTemplate::Cast(Data* data) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(data);
  #endif
    return reinterpret_cast<ObjectTemplate*>(data);
  }
  
  Signature* Signature::Cast(Data* data) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(data);
  #endif
    return reinterpret_cast<Signature*>(data);
  }
  
  AccessorSignature* AccessorSignature::Cast(Data* data) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(data);
  #endif
    return reinterpret_cast<AccessorSignature*>(data);
  }
  
  Local<Value> Object::GetInternalField(int index) {
  #ifndef V8_ENABLE_CHECKS
    typedef internal::Address A;
    typedef internal::Internals I;
    A obj = *reinterpret_cast<A*>(this);
    // Fast path: If the object is a plain JSObject, which is the common case, we
    // know where to find the internal fields and can return the value directly.
    auto instance_type = I::GetInstanceType(obj);
    if (instance_type == I::kJSObjectType ||
        instance_type == I::kJSApiObjectType ||
        instance_type == I::kJSSpecialApiObjectType) {
      int offset = I::kJSObjectHeaderSize + (I::kEmbedderDataSlotSize * index);
      A value = I::ReadRawField<A>(obj, offset);
  #ifdef V8_COMPRESS_POINTERS
      // We read the full pointer value and then decompress it in order to avoid
      // dealing with potential endiannes issues.
      value = I::DecompressTaggedAnyField(obj, static_cast<int32_t>(value));
  #endif
      internal::Isolate* isolate =
          internal::IsolateFromNeverReadOnlySpaceObject(obj);
      A* result = HandleScope::CreateHandle(isolate, value);
      return Local<Value>(reinterpret_cast<Value*>(result));
    }
  #endif
    return SlowGetInternalField(index);
  }
  
  
  void* Object::GetAlignedPointerFromInternalField(int index) {
  #ifndef V8_ENABLE_CHECKS
    typedef internal::Address A;
    typedef internal::Internals I;
    A obj = *reinterpret_cast<A*>(this);
    // Fast path: If the object is a plain JSObject, which is the common case, we
    // know where to find the internal fields and can return the value directly.
    auto instance_type = I::GetInstanceType(obj);
    if (V8_LIKELY(instance_type == I::kJSObjectType ||
                  instance_type == I::kJSApiObjectType ||
                  instance_type == I::kJSSpecialApiObjectType)) {
      int offset = I::kJSObjectHeaderSize + (I::kEmbedderDataSlotSize * index);
      return I::ReadRawField<void*>(obj, offset);
    }
  #endif
    return SlowGetAlignedPointerFromInternalField(index);
  }
  
  String* String::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<String*>(value);
  }
  
  
  Local<String> String::Empty(Isolate* isolate) {
    typedef internal::Address S;
    typedef internal::Internals I;
    I::CheckInitialized(isolate);
    S* slot = I::GetRoot(isolate, I::kEmptyStringRootIndex);
    return Local<String>(reinterpret_cast<String*>(slot));
  }
  
  
  String::ExternalStringResource* String::GetExternalStringResource() const {
    typedef internal::Address A;
    typedef internal::Internals I;
    A obj = *reinterpret_cast<const A*>(this);
  
    ExternalStringResource* result;
    if (I::IsExternalTwoByteString(I::GetInstanceType(obj))) {
      void* value = I::ReadRawField<void*>(obj, I::kStringResourceOffset);
      result = reinterpret_cast<String::ExternalStringResource*>(value);
    } else {
      result = GetExternalStringResourceSlow();
    }
  #ifdef V8_ENABLE_CHECKS
    VerifyExternalStringResource(result);
  #endif
    return result;
  }
  
  
  String::ExternalStringResourceBase* String::GetExternalStringResourceBase(
      String::Encoding* encoding_out) const {
    typedef internal::Address A;
    typedef internal::Internals I;
    A obj = *reinterpret_cast<const A*>(this);
    int type = I::GetInstanceType(obj) & I::kFullStringRepresentationMask;
    *encoding_out = static_cast<Encoding>(type & I::kStringEncodingMask);
    ExternalStringResourceBase* resource;
    if (type == I::kExternalOneByteRepresentationTag ||
        type == I::kExternalTwoByteRepresentationTag) {
      void* value = I::ReadRawField<void*>(obj, I::kStringResourceOffset);
      resource = static_cast<ExternalStringResourceBase*>(value);
    } else {
      resource = GetExternalStringResourceBaseSlow(encoding_out);
    }
  #ifdef V8_ENABLE_CHECKS
    VerifyExternalStringResourceBase(resource, *encoding_out);
  #endif
    return resource;
  }
  
  
  bool Value::IsUndefined() const {
  #ifdef V8_ENABLE_CHECKS
    return FullIsUndefined();
  #else
    return QuickIsUndefined();
  #endif
  }
  
  bool Value::QuickIsUndefined() const {
    typedef internal::Address A;
    typedef internal::Internals I;
    A obj = *reinterpret_cast<const A*>(this);
    if (!I::HasHeapObjectTag(obj)) return false;
    if (I::GetInstanceType(obj) != I::kOddballType) return false;
    return (I::GetOddballKind(obj) == I::kUndefinedOddballKind);
  }
  
  
  bool Value::IsNull() const {
  #ifdef V8_ENABLE_CHECKS
    return FullIsNull();
  #else
    return QuickIsNull();
  #endif
  }
  
  bool Value::QuickIsNull() const {
    typedef internal::Address A;
    typedef internal::Internals I;
    A obj = *reinterpret_cast<const A*>(this);
    if (!I::HasHeapObjectTag(obj)) return false;
    if (I::GetInstanceType(obj) != I::kOddballType) return false;
    return (I::GetOddballKind(obj) == I::kNullOddballKind);
  }
  
  bool Value::IsNullOrUndefined() const {
  #ifdef V8_ENABLE_CHECKS
    return FullIsNull() || FullIsUndefined();
  #else
    return QuickIsNullOrUndefined();
  #endif
  }
  
  bool Value::QuickIsNullOrUndefined() const {
    typedef internal::Address A;
    typedef internal::Internals I;
    A obj = *reinterpret_cast<const A*>(this);
    if (!I::HasHeapObjectTag(obj)) return false;
    if (I::GetInstanceType(obj) != I::kOddballType) return false;
    int kind = I::GetOddballKind(obj);
    return kind == I::kNullOddballKind || kind == I::kUndefinedOddballKind;
  }
  
  bool Value::IsString() const {
  #ifdef V8_ENABLE_CHECKS
    return FullIsString();
  #else
    return QuickIsString();
  #endif
  }
  
  bool Value::QuickIsString() const {
    typedef internal::Address A;
    typedef internal::Internals I;
    A obj = *reinterpret_cast<const A*>(this);
    if (!I::HasHeapObjectTag(obj)) return false;
    return (I::GetInstanceType(obj) < I::kFirstNonstringType);
  }
  
  
  template <class T> Value* Value::Cast(T* value) {
    return static_cast<Value*>(value);
  }
  
  
  Boolean* Boolean::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Boolean*>(value);
  }
  
  
  Name* Name::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Name*>(value);
  }
  
  
  Symbol* Symbol::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Symbol*>(value);
  }
  
  
  Private* Private::Cast(Data* data) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(data);
  #endif
    return reinterpret_cast<Private*>(data);
  }
  
  
  Number* Number::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Number*>(value);
  }
  
  
  Integer* Integer::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Integer*>(value);
  }
  
  
  Int32* Int32::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Int32*>(value);
  }
  
  
  Uint32* Uint32::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Uint32*>(value);
  }
  
  BigInt* BigInt::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<BigInt*>(value);
  }
  
  Date* Date::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Date*>(value);
  }
  
  
  StringObject* StringObject::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<StringObject*>(value);
  }
  
  
  SymbolObject* SymbolObject::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<SymbolObject*>(value);
  }
  
  
  NumberObject* NumberObject::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<NumberObject*>(value);
  }
  
  BigIntObject* BigIntObject::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<BigIntObject*>(value);
  }
  
  BooleanObject* BooleanObject::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<BooleanObject*>(value);
  }
  
  
  RegExp* RegExp::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<RegExp*>(value);
  }
  
  
  Object* Object::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Object*>(value);
  }
  
  
  Array* Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Array*>(value);
  }
  
  
  Map* Map::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Map*>(value);
  }
  
  
  Set* Set::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Set*>(value);
  }
  
  
  Promise* Promise::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Promise*>(value);
  }
  
  
  Proxy* Proxy::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Proxy*>(value);
  }
  
  WasmModuleObject* WasmModuleObject::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<WasmModuleObject*>(value);
  }
  
  Promise::Resolver* Promise::Resolver::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Promise::Resolver*>(value);
  }
  
  
  ArrayBuffer* ArrayBuffer::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<ArrayBuffer*>(value);
  }
  
  
  ArrayBufferView* ArrayBufferView::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<ArrayBufferView*>(value);
  }
  
  
  TypedArray* TypedArray::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<TypedArray*>(value);
  }
  
  
  Uint8Array* Uint8Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Uint8Array*>(value);
  }
  
  
  Int8Array* Int8Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Int8Array*>(value);
  }
  
  
  Uint16Array* Uint16Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Uint16Array*>(value);
  }
  
  
  Int16Array* Int16Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Int16Array*>(value);
  }
  
  
  Uint32Array* Uint32Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Uint32Array*>(value);
  }
  
  
  Int32Array* Int32Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Int32Array*>(value);
  }
  
  
  Float32Array* Float32Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Float32Array*>(value);
  }
  
  
  Float64Array* Float64Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Float64Array*>(value);
  }
  
  BigInt64Array* BigInt64Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<BigInt64Array*>(value);
  }
  
  BigUint64Array* BigUint64Array::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<BigUint64Array*>(value);
  }
  
  Uint8ClampedArray* Uint8ClampedArray::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Uint8ClampedArray*>(value);
  }
  
  
  DataView* DataView::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<DataView*>(value);
  }
  
  
  SharedArrayBuffer* SharedArrayBuffer::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<SharedArrayBuffer*>(value);
  }
  
  
  Function* Function::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<Function*>(value);
  }
  
  
  External* External::Cast(v8::Value* value) {
  #ifdef V8_ENABLE_CHECKS
    CheckCast(value);
  #endif
    return static_cast<External*>(value);
  }
  
  
  template<typename T>
  Isolate* PropertyCallbackInfo<T>::GetIsolate() const {
    return *reinterpret_cast<Isolate**>(&args_[kIsolateIndex]);
  }
  
  
  template<typename T>
  Local<Value> PropertyCallbackInfo<T>::Data() const {
    return Local<Value>(reinterpret_cast<Value*>(&args_[kDataIndex]));
  }
  
  
  template<typename T>
  Local<Object> PropertyCallbackInfo<T>::This() const {
    return Local<Object>(reinterpret_cast<Object*>(&args_[kThisIndex]));
  }
  
  
  template<typename T>
  Local<Object> PropertyCallbackInfo<T>::Holder() const {
    return Local<Object>(reinterpret_cast<Object*>(&args_[kHolderIndex]));
  }
  
  
  template<typename T>
  ReturnValue<T> PropertyCallbackInfo<T>::GetReturnValue() const {
    return ReturnValue<T>(&args_[kReturnValueIndex]);
  }
  
  template <typename T>
  bool PropertyCallbackInfo<T>::ShouldThrowOnError() const {
    typedef internal::Internals I;
    if (args_[kShouldThrowOnErrorIndex] !=
        I::IntToSmi(I::kInferShouldThrowMode)) {
      return args_[kShouldThrowOnErrorIndex] != I::IntToSmi(I::kDontThrow);
    }
    return v8::internal::ShouldThrowOnError(
        reinterpret_cast<v8::internal::Isolate*>(GetIsolate()));
  }
  
  Local<Primitive> Undefined(Isolate* isolate) {
    typedef internal::Address S;
    typedef internal::Internals I;
    I::CheckInitialized(isolate);
    S* slot = I::GetRoot(isolate, I::kUndefinedValueRootIndex);
    return Local<Primitive>(reinterpret_cast<Primitive*>(slot));
  }
  
  
  Local<Primitive> Null(Isolate* isolate) {
    typedef internal::Address S;
    typedef internal::Internals I;
    I::CheckInitialized(isolate);
    S* slot = I::GetRoot(isolate, I::kNullValueRootIndex);
    return Local<Primitive>(reinterpret_cast<Primitive*>(slot));
  }
  
  
  Local<Boolean> True(Isolate* isolate) {
    typedef internal::Address S;
    typedef internal::Internals I;
    I::CheckInitialized(isolate);
    S* slot = I::GetRoot(isolate, I::kTrueValueRootIndex);
    return Local<Boolean>(reinterpret_cast<Boolean*>(slot));
  }
  
  
  Local<Boolean> False(Isolate* isolate) {
    typedef internal::Address S;
    typedef internal::Internals I;
    I::CheckInitialized(isolate);
    S* slot = I::GetRoot(isolate, I::kFalseValueRootIndex);
    return Local<Boolean>(reinterpret_cast<Boolean*>(slot));
  }
  
  
  void Isolate::SetData(uint32_t slot, void* data) {
    typedef internal::Internals I;
    I::SetEmbedderData(this, slot, data);
  }
  
  
  void* Isolate::GetData(uint32_t slot) {
    typedef internal::Internals I;
    return I::GetEmbedderData(this, slot);
  }
  
  
  uint32_t Isolate::GetNumberOfDataSlots() {
    typedef internal::Internals I;
    return I::kNumIsolateDataSlots;
  }
  
  template <class T>
  MaybeLocal<T> Isolate::GetDataFromSnapshotOnce(size_t index) {
    T* data = reinterpret_cast<T*>(GetDataFromSnapshotOnce(index));
    if (data) internal::PerformCastCheck(data);
    return Local<T>(data);
  }
  
  int64_t Isolate::AdjustAmountOfExternalAllocatedMemory(
      int64_t change_in_bytes) {
    typedef internal::Internals I;
    constexpr int64_t kMemoryReducerActivationLimit = 32 * 1024 * 1024;
    int64_t* external_memory = reinterpret_cast<int64_t*>(
        reinterpret_cast<uint8_t*>(this) + I::kExternalMemoryOffset);
    int64_t* external_memory_limit = reinterpret_cast<int64_t*>(
        reinterpret_cast<uint8_t*>(this) + I::kExternalMemoryLimitOffset);
    int64_t* external_memory_at_last_mc =
        reinterpret_cast<int64_t*>(reinterpret_cast<uint8_t*>(this) +
                                   I::kExternalMemoryAtLastMarkCompactOffset);
  
    // Embedders are weird: we see both over- and underflows here. Perform the
    // addition with unsigned types to avoid undefined behavior.
    const int64_t amount =
        static_cast<int64_t>(static_cast<uint64_t>(change_in_bytes) +
                             static_cast<uint64_t>(*external_memory));
    *external_memory = amount;
  
    int64_t allocation_diff_since_last_mc =
        static_cast<int64_t>(static_cast<uint64_t>(*external_memory) -
                             static_cast<uint64_t>(*external_memory_at_last_mc));
    // Only check memory pressure and potentially trigger GC if the amount of
    // external memory increased.
    if (allocation_diff_since_last_mc > kMemoryReducerActivationLimit) {
      CheckMemoryPressure();
    }
  
    if (change_in_bytes < 0) {
      const int64_t lower_limit = *external_memory_limit + change_in_bytes;
      if (lower_limit > I::kExternalAllocationSoftLimit)
        *external_memory_limit = lower_limit;
    } else if (change_in_bytes > 0 && amount > *external_memory_limit) {
      ReportExternalAllocationLimitReached();
    }
    return *external_memory;
  }
  
  Local<Value> Context::GetEmbedderData(int index) {
  #ifndef V8_ENABLE_CHECKS
    typedef internal::Address A;
    typedef internal::Internals I;
    A ctx = *reinterpret_cast<const A*>(this);
    A embedder_data =
        I::ReadTaggedPointerField(ctx, I::kNativeContextEmbedderDataOffset);
    int value_offset =
        I::kEmbedderDataArrayHeaderSize + (I::kEmbedderDataSlotSize * index);
    A value = I::ReadRawField<A>(embedder_data, value_offset);
  #ifdef V8_COMPRESS_POINTERS
    // We read the full pointer value and then decompress it in order to avoid
    // dealing with potential endiannes issues.
    value =
        I::DecompressTaggedAnyField(embedder_data, static_cast<int32_t>(value));
  #endif
    internal::Isolate* isolate = internal::IsolateFromNeverReadOnlySpaceObject(
        *reinterpret_cast<A*>(this));
    A* result = HandleScope::CreateHandle(isolate, value);
    return Local<Value>(reinterpret_cast<Value*>(result));
  #else
    return SlowGetEmbedderData(index);
  #endif
  }
  
  
  void* Context::GetAlignedPointerFromEmbedderData(int index) {
  #ifndef V8_ENABLE_CHECKS
    typedef internal::Address A;
    typedef internal::Internals I;
    A ctx = *reinterpret_cast<const A*>(this);
    A embedder_data =
        I::ReadTaggedPointerField(ctx, I::kNativeContextEmbedderDataOffset);
    int value_offset =
        I::kEmbedderDataArrayHeaderSize + (I::kEmbedderDataSlotSize * index);
    return I::ReadRawField<void*>(embedder_data, value_offset);
  #else
    return SlowGetAlignedPointerFromEmbedderData(index);
  #endif
  }
  
  template <class T>
  MaybeLocal<T> Context::GetDataFromSnapshotOnce(size_t index) {
    T* data = reinterpret_cast<T*>(GetDataFromSnapshotOnce(index));
    if (data) internal::PerformCastCheck(data);
    return Local<T>(data);
  }
  
  template <class T>
  size_t SnapshotCreator::AddData(Local<Context> context, Local<T> object) {
    T* object_ptr = *object;
    internal::Address* p = reinterpret_cast<internal::Address*>(object_ptr);
    return AddData(context, *p);
  }
  
  template <class T>
  size_t SnapshotCreator::AddData(Local<T> object) {
    T* object_ptr = *object;
    internal::Address* p = reinterpret_cast<internal::Address*>(object_ptr);
    return AddData(*p);
  }
  
  /**
   * \example shell.cc
   * A simple shell that takes a list of expressions on the
   * command-line and executes them.
   */
  
  
  /**
   * \example process.cc
   */
  
  
  }  // namespace v8
  
  
  #undef TYPE_CHECK
  
  
  #endif  // INCLUDE_V8_H_
  