text: // Copyright (c) 2012 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // Scopers help you manage ownership of a pointer, helping you easily manage the
  // a pointer within a scope, and automatically destroying the pointer at the
  // end of a scope.  There are two main classes you will use, which correspond
  // to the operators new/delete and new[]/delete[].
  //
  // Example usage (scoped_ptr):
  //   {
  //     scoped_ptr<Foo> foo(new Foo("wee"));
  //   }  // foo goes out of scope, releasing the pointer with it.
  //
  //   {
  //     scoped_ptr<Foo> foo;          // No pointer managed.
  //     foo.reset(new Foo("wee"));    // Now a pointer is managed.
  //     foo.reset(new Foo("wee2"));   // Foo("wee") was destroyed.
  //     foo.reset(new Foo("wee3"));   // Foo("wee2") was destroyed.
  //     foo->Method();                // Foo::Method() called.
  //     foo.get()->Method();          // Foo::Method() called.
  //     SomeFunc(foo.release());      // SomeFunc takes ownership, foo no longer
  //                                   // manages a pointer.
  //     foo.reset(new Foo("wee4"));   // foo manages a pointer again.
  //     foo.reset();                  // Foo("wee4") destroyed, foo no longer
  //                                   // manages a pointer.
  //   }  // foo wasn't managing a pointer, so nothing was destroyed.
  //
  // Example usage (scoped_array):
  //   {
  //     scoped_array<Foo> foo(new Foo[100]);
  //     foo.get()->Method();  // Foo::Method on the 0th element.
  //     foo[10].Method();     // Foo::Method on the 10th element.
  //   }
  //
  // These scopers also implement part of the functionality of C++11 unique_ptr
  // in that they are "movable but not copyable."  You can use the scopers in
  // the parameter and return types of functions to signify ownership transfer
  // in to and out of a function.  When calling a function that has a scoper
  // as the argument type, it must be called with the result of an analogous
  // scoper's Pass() function or another function that generates a temporary;
  // passing by copy will NOT work.  Here is an example using scoped_ptr:
  //
  //   void TakesOwnership(scoped_ptr<Foo> arg) {
  //     // Do something with arg
  //   }
  //   scoped_ptr<Foo> CreateFoo() {
  //     // No need for calling Pass() because we are constructing a temporary
  //     // for the return value.
  //     return scoped_ptr<Foo>(new Foo("new"));
  //   }
  //   scoped_ptr<Foo> PassThru(scoped_ptr<Foo> arg) {
  //     return arg.Pass();
  //   }
  //
  //   {
  //     scoped_ptr<Foo> ptr(new Foo("yay"));  // ptr manages Foo("yay").
  //     TakesOwnership(ptr.Pass());           // ptr no longer owns Foo("yay").
  //     scoped_ptr<Foo> ptr2 = CreateFoo();   // ptr2 owns the return Foo.
  //     scoped_ptr<Foo> ptr3 =                // ptr3 now owns what was in ptr2.
  //         PassThru(ptr2.Pass());            // ptr2 is correspondingly NULL.
  //   }
  //
  // Notice that if you do not call Pass() when returning from PassThru(), or
  // when invoking TakesOwnership(), the code will not compile because scopers
  // are not copyable; they only implement move semantics which require calling
  // the Pass() function to signify a destructive transfer of state. CreateFoo()
  // is different though because we are constructing a temporary on the return
  // line and thus can avoid needing to call Pass().
  //
  // Pass() properly handles upcast in assignment, i.e. you can assign
  // scoped_ptr<Child> to scoped_ptr<Parent>:
  //
  //   scoped_ptr<Foo> foo(new Foo());
  //   scoped_ptr<FooParent> parent = foo.Pass();
  //
  // PassAs<>() should be used to upcast return value in return statement:
  //
  //   scoped_ptr<Foo> CreateFoo() {
  //     scoped_ptr<FooChild> result(new FooChild());
  //     return result.PassAs<Foo>();
  //   }
  //
  // Note that PassAs<>() is implemented only for scoped_ptr, but not for
  // scoped_array. This is because casting array pointers may not be safe.
  
  #ifndef BASE_MEMORY_SCOPED_PTR_H_
  #define BASE_MEMORY_SCOPED_PTR_H_
  
  // This is an implementation designed to match the anticipated future TR2
  // implementation of the scoped_ptr class, and its closely-related brethren,
  // scoped_array, scoped_ptr_malloc.
  
  #include <assert.h>
  #include <stddef.h>
  #include <stdlib.h>
  
  #include "base/basictypes.h"
  #include "base/compiler_specific.h"
  #include "base/move.h"
  #include "base/template_util.h"
  
  namespace base {
  
  namespace subtle {
  class RefCountedBase;
  class RefCountedThreadSafeBase;
  }  // namespace subtle
  
  namespace internal {
  
  template <typename T> struct IsNotRefCounted {
    enum {
      value = !base::is_convertible<T*, base::subtle::RefCountedBase*>::value &&
          !base::is_convertible<T*, base::subtle::RefCountedThreadSafeBase*>::
              value
    };
  };
  
  }  // namespace internal
  }  // namespace base
  
  // A scoped_ptr<T> is like a T*, except that the destructor of scoped_ptr<T>
  // automatically deletes the pointer it holds (if any).
  // That is, scoped_ptr<T> owns the T object that it points to.
  // Like a T*, a scoped_ptr<T> may hold either NULL or a pointer to a T object.
  // Also like T*, scoped_ptr<T> is thread-compatible, and once you
  // dereference it, you get the thread safety guarantees of T.
  //
  // The size of a scoped_ptr is small:
  // sizeof(scoped_ptr<C>) == sizeof(C*)
  template <class C>
  class scoped_ptr {
    MOVE_ONLY_TYPE_FOR_CPP_03(scoped_ptr, RValue)
  
    COMPILE_ASSERT(base::internal::IsNotRefCounted<C>::value,
                   C_is_refcounted_type_and_needs_scoped_refptr);
  
   public:
  
    // The element type
    typedef C element_type;
  
    // Constructor.  Defaults to initializing with NULL.
    // There is no way to create an uninitialized scoped_ptr.
    // The input parameter must be allocated with new.
    explicit scoped_ptr(C* p = NULL) : ptr_(p) { }
  
    // Constructor.  Allows construction from a scoped_ptr rvalue for a
    // convertible type.
    template <typename U>
    scoped_ptr(scoped_ptr<U> other) : ptr_(other.release()) { }
  
    // Constructor.  Move constructor for C++03 move emulation of this type.
    scoped_ptr(RValue rvalue)
        : ptr_(rvalue.object->release()) {
    }
  
    // Destructor.  If there is a C object, delete it.
    // We don't need to test ptr_ == NULL because C++ does that for us.
    ~scoped_ptr() {
      enum { type_must_be_complete = sizeof(C) };
      delete ptr_;
    }
  
    // operator=.  Allows assignment from a scoped_ptr rvalue for a convertible
    // type.
    template <typename U>
    scoped_ptr& operator=(scoped_ptr<U> rhs) {
      reset(rhs.release());
      return *this;
    }
  
    // operator=.  Move operator= for C++03 move emulation of this type.
    scoped_ptr& operator=(RValue rhs) {
      swap(*rhs->object);
      return *this;
    }
  
    // Reset.  Deletes the current owned object, if any.
    // Then takes ownership of a new object, if given.
    // this->reset(this->get()) works.
    void reset(C* p = NULL) {
      if (p != ptr_) {
        enum { type_must_be_complete = sizeof(C) };
        delete ptr_;
        ptr_ = p;
      }
    }
  
    // Accessors to get the owned object.
    // operator* and operator-> will assert() if there is no current object.
    C& operator*() const {
      assert(ptr_ != NULL);
      return *ptr_;
    }
    C* operator->() const  {
      assert(ptr_ != NULL);
      return ptr_;
    }
    C* get() const { return ptr_; }
  
    // Allow scoped_ptr<C> to be used in boolean expressions, but not
    // implicitly convertible to a real bool (which is dangerous).
    typedef C* scoped_ptr::*Testable;
    operator Testable() const { return ptr_ ? &scoped_ptr::ptr_ : NULL; }
  
    // Comparison operators.
    // These return whether two scoped_ptr refer to the same object, not just to
    // two different but equal objects.
    bool operator==(C* p) const { return ptr_ == p; }
    bool operator!=(C* p) const { return ptr_ != p; }
  
    // Swap two scoped pointers.
    void swap(scoped_ptr& p2) {
      C* tmp = ptr_;
      ptr_ = p2.ptr_;
      p2.ptr_ = tmp;
    }
  
    // Release a pointer.
    // The return value is the current pointer held by this object.
    // If this object holds a NULL pointer, the return value is NULL.
    // After this operation, this object will hold a NULL pointer,
    // and will not own the object any more.
    C* release() WARN_UNUSED_RESULT {
      C* retVal = ptr_;
      ptr_ = NULL;
      return retVal;
    }
  
    template <typename PassAsType>
    scoped_ptr<PassAsType> PassAs() {
      return scoped_ptr<PassAsType>(release());
    }
  
   private:
    C* ptr_;
  
    // Forbid comparison of scoped_ptr types.  If C2 != C, it totally doesn't
    // make sense, and if C2 == C, it still doesn't make sense because you should
    // never have the same object owned by two different scoped_ptrs.
    template <class C2> bool operator==(scoped_ptr<C2> const& p2) const;
    template <class C2> bool operator!=(scoped_ptr<C2> const& p2) const;
  
  };
  
  // Free functions
  template <class C>
  void swap(scoped_ptr<C>& p1, scoped_ptr<C>& p2) {
    p1.swap(p2);
  }
  
  template <class C>
  bool operator==(C* p1, const scoped_ptr<C>& p2) {
    return p1 == p2.get();
  }
  
  template <class C>
  bool operator!=(C* p1, const scoped_ptr<C>& p2) {
    return p1 != p2.get();
  }
  
  // scoped_array<C> is like scoped_ptr<C>, except that the caller must allocate
  // with new [] and the destructor deletes objects with delete [].
  //
  // As with scoped_ptr<C>, a scoped_array<C> either points to an object
  // or is NULL.  A scoped_array<C> owns the object that it points to.
  // scoped_array<T> is thread-compatible, and once you index into it,
  // the returned objects have only the thread safety guarantees of T.
  //
  // Size: sizeof(scoped_array<C>) == sizeof(C*)
  template <class C>
  class scoped_array {
    MOVE_ONLY_TYPE_FOR_CPP_03(scoped_array, RValue)
  
   public:
  
    // The element type
    typedef C element_type;
  
    // Constructor.  Defaults to initializing with NULL.
    // There is no way to create an uninitialized scoped_array.
    // The input parameter must be allocated with new [].
    explicit scoped_array(C* p = NULL) : array_(p) { }
  
    // Constructor.  Move constructor for C++03 move emulation of this type.
    scoped_array(RValue rvalue)
        : array_(rvalue.object->release()) {
    }
  
    // Destructor.  If there is a C object, delete it.
    // We don't need to test ptr_ == NULL because C++ does that for us.
    ~scoped_array() {
      enum { type_must_be_complete = sizeof(C) };
      delete[] array_;
    }
  
    // operator=.  Move operator= for C++03 move emulation of this type.
    scoped_array& operator=(RValue rhs) {
      swap(*rhs.object);
      return *this;
    }
  
    // Reset.  Deletes the current owned object, if any.
    // Then takes ownership of a new object, if given.
    // this->reset(this->get()) works.
    void reset(C* p = NULL) {
      if (p != array_) {
        enum { type_must_be_complete = sizeof(C) };
        delete[] array_;
        array_ = p;
      }
    }
  
    // Get one element of the current object.
    // Will assert() if there is no current object, or index i is negative.
    C& operator[](ptrdiff_t i) const {
      assert(i >= 0);
      assert(array_ != NULL);
      return array_[i];
    }
  
    // Get a pointer to the zeroth element of the current object.
    // If there is no current object, return NULL.
    C* get() const {
      return array_;
    }
  
    // Allow scoped_array<C> to be used in boolean expressions, but not
    // implicitly convertible to a real bool (which is dangerous).
    typedef C* scoped_array::*Testable;
    operator Testable() const { return array_ ? &scoped_array::array_ : NULL; }
  
    // Comparison operators.
    // These return whether two scoped_array refer to the same object, not just to
    // two different but equal objects.
    bool operator==(C* p) const { return array_ == p; }
    bool operator!=(C* p) const { return array_ != p; }
  
    // Swap two scoped arrays.
    void swap(scoped_array& p2) {
      C* tmp = array_;
      array_ = p2.array_;
      p2.array_ = tmp;
    }
  
    // Release an array.
    // The return value is the current pointer held by this object.
    // If this object holds a NULL pointer, the return value is NULL.
    // After this operation, this object will hold a NULL pointer,
    // and will not own the object any more.
    C* release() WARN_UNUSED_RESULT {
      C* retVal = array_;
      array_ = NULL;
      return retVal;
    }
  
   private:
    C* array_;
  
    // Forbid comparison of different scoped_array types.
    template <class C2> bool operator==(scoped_array<C2> const& p2) const;
    template <class C2> bool operator!=(scoped_array<C2> const& p2) const;
  };
  
  // Free functions
  template <class C>
  void swap(scoped_array<C>& p1, scoped_array<C>& p2) {
    p1.swap(p2);
  }
  
  template <class C>
  bool operator==(C* p1, const scoped_array<C>& p2) {
    return p1 == p2.get();
  }
  
  template <class C>
  bool operator!=(C* p1, const scoped_array<C>& p2) {
    return p1 != p2.get();
  }
  
  // This class wraps the c library function free() in a class that can be
  // passed as a template argument to scoped_ptr_malloc below.
  class ScopedPtrMallocFree {
   public:
    inline void operator()(void* x) const {
      free(x);
    }
  };
  
  // scoped_ptr_malloc<> is similar to scoped_ptr<>, but it accepts a
  // second template argument, the functor used to free the object.
  
  template<class C, class FreeProc = ScopedPtrMallocFree>
  class scoped_ptr_malloc {
    MOVE_ONLY_TYPE_FOR_CPP_03(scoped_ptr_malloc, RValue)
  
   public:
  
    // The element type
    typedef C element_type;
  
    // Constructor.  Defaults to initializing with NULL.
    // There is no way to create an uninitialized scoped_ptr.
    // The input parameter must be allocated with an allocator that matches the
    // Free functor.  For the default Free functor, this is malloc, calloc, or
    // realloc.
    explicit scoped_ptr_malloc(C* p = NULL): ptr_(p) {}
  
    // Constructor.  Move constructor for C++03 move emulation of this type.
    scoped_ptr_malloc(RValue rvalue)
        : ptr_(rvalue.object->release()) {
    }
  
    // Destructor.  If there is a C object, call the Free functor.
    ~scoped_ptr_malloc() {
      reset();
    }
  
    // operator=.  Move operator= for C++03 move emulation of this type.
    scoped_ptr_malloc& operator=(RValue rhs) {
      swap(*rhs.object);
      return *this;
    }
  
    // Reset.  Calls the Free functor on the current owned object, if any.
    // Then takes ownership of a new object, if given.
    // this->reset(this->get()) works.
    void reset(C* p = NULL) {
      if (ptr_ != p) {
        FreeProc free_proc;
        free_proc(ptr_);
        ptr_ = p;
      }
    }
  
    // Get the current object.
    // operator* and operator-> will cause an assert() failure if there is
    // no current object.
    C& operator*() const {
      assert(ptr_ != NULL);
      return *ptr_;
    }
  
    C* operator->() const {
      assert(ptr_ != NULL);
      return ptr_;
    }
  
    C* get() const {
      return ptr_;
    }
  
    // Allow scoped_ptr_malloc<C> to be used in boolean expressions, but not
    // implicitly convertible to a real bool (which is dangerous).
    typedef C* scoped_ptr_malloc::*Testable;
    operator Testable() const { return ptr_ ? &scoped_ptr_malloc::ptr_ : NULL; }
  
    // Comparison operators.
    // These return whether a scoped_ptr_malloc and a plain pointer refer
    // to the same object, not just to two different but equal objects.
    // For compatibility with the boost-derived implementation, these
    // take non-const arguments.
    bool operator==(C* p) const {
      return ptr_ == p;
    }
  
    bool operator!=(C* p) const {
      return ptr_ != p;
    }
  
    // Swap two scoped pointers.
    void swap(scoped_ptr_malloc & b) {
      C* tmp = b.ptr_;
      b.ptr_ = ptr_;
      ptr_ = tmp;
    }
  
    // Release a pointer.
    // The return value is the current pointer held by this object.
    // If this object holds a NULL pointer, the return value is NULL.
    // After this operation, this object will hold a NULL pointer,
    // and will not own the object any more.
    C* release() WARN_UNUSED_RESULT {
      C* tmp = ptr_;
      ptr_ = NULL;
      return tmp;
    }
  
   private:
    C* ptr_;
  
    // no reason to use these: each scoped_ptr_malloc should have its own object
    template <class C2, class GP>
    bool operator==(scoped_ptr_malloc<C2, GP> const& p) const;
    template <class C2, class GP>
    bool operator!=(scoped_ptr_malloc<C2, GP> const& p) const;
  };
  
  template<class C, class FP> inline
  void swap(scoped_ptr_malloc<C, FP>& a, scoped_ptr_malloc<C, FP>& b) {
    a.swap(b);
  }
  
  template<class C, class FP> inline
  bool operator==(C* p, const scoped_ptr_malloc<C, FP>& b) {
    return p == b.get();
  }
  
  template<class C, class FP> inline
  bool operator!=(C* p, const scoped_ptr_malloc<C, FP>& b) {
    return p != b.get();
  }
  
  // A function to convert T* into scoped_ptr<T>
  // Doing e.g. make_scoped_ptr(new FooBarBaz<type>(arg)) is a shorter notation
  // for scoped_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
  template <typename T>
  scoped_ptr<T> make_scoped_ptr(T* ptr) {
    return scoped_ptr<T>(ptr);
  }
  
  #endif  // BASE_MEMORY_SCOPED_PTR_H_
  