text: /*
   * Copyright 2014 Facebook, Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #ifndef FOLLY_DYNAMIC_INL_H_
  #define FOLLY_DYNAMIC_INL_H_
  
  #include <functional>
  #include <boost/iterator/iterator_adaptor.hpp>
  #include <boost/iterator/iterator_facade.hpp>
  #include <folly/Likely.h>
  #include <folly/Conv.h>
  #include <folly/Format.h>
  
  //////////////////////////////////////////////////////////////////////
  
  namespace std {
  
  template<>
  struct hash< ::folly::dynamic> {
    size_t operator()(::folly::dynamic const& d) const {
      return d.hash();
    }
  };
  
  }
  
  //////////////////////////////////////////////////////////////////////
  
  // This is a higher-order preprocessor macro to aid going from runtime
  // types to the compile time type system.
  #define FB_DYNAMIC_APPLY(type, apply) do {         \
    switch ((type)) {                             \
    case NULLT:   apply(void*);          break;   \
    case ARRAY:   apply(Array);          break;   \
    case BOOL:    apply(bool);           break;   \
    case DOUBLE:  apply(double);         break;   \
    case INT64:   apply(int64_t);        break;   \
    case OBJECT:  apply(ObjectImpl);     break;   \
    case STRING:  apply(fbstring);       break;   \
    default:      CHECK(0); abort();              \
    }                                             \
  } while (0)
  
  //////////////////////////////////////////////////////////////////////
  
  namespace folly {
  
  struct TypeError : std::runtime_error {
    explicit TypeError(const std::string& expected, dynamic::Type actual)
      : std::runtime_error(to<std::string>("TypeError: expected dynamic "
          "type `", expected, '\'', ", but had type `",
          dynamic::typeName(actual), '\''))
    {}
    explicit TypeError(const std::string& expected,
        dynamic::Type actual1, dynamic::Type actual2)
      : std::runtime_error(to<std::string>("TypeError: expected dynamic "
          "types `", expected, '\'', ", but had types `",
          dynamic::typeName(actual1), "' and `", dynamic::typeName(actual2),
          '\''))
    {}
  };
  
  
  //////////////////////////////////////////////////////////////////////
  
  namespace detail {
  
    // This helper is used in destroy() to be able to run destructors on
    // types like "int64_t" without a compiler error.
    struct Destroy {
      template<class T> static void destroy(T* t) { t->~T(); }
    };
  
    /*
     * The enable_if junk here is necessary to avoid ambiguous
     * conversions relating to bool and double when you implicitly
     * convert an int or long to a dynamic.
     */
    template<class T, class Enable = void> struct ConversionHelper;
    template<class T>
    struct ConversionHelper<
      T,
      typename std::enable_if<
        std::is_integral<T>::value && !std::is_same<T,bool>::value
      >::type
    > {
      typedef int64_t type;
    };
    template<class T>
    struct ConversionHelper<
      T,
      typename std::enable_if<
        (!std::is_integral<T>::value || std::is_same<T,bool>::value) &&
        !std::is_same<T,std::nullptr_t>::value
      >::type
    > {
      typedef T type;
    };
    template<class T>
    struct ConversionHelper<
      T,
      typename std::enable_if<
        std::is_same<T,std::nullptr_t>::value
      >::type
    > {
      typedef void* type;
    };
  
    /*
     * Helper for implementing numeric conversions in operators on
     * numbers.  Just promotes to double when one of the arguments is
     * double, or throws if either is not a numeric type.
     */
    template<template<class> class Op>
    dynamic numericOp(dynamic const& a, dynamic const& b) {
      if (!a.isNumber() || !b.isNumber()) {
        throw TypeError("numeric", a.type(), b.type());
      }
      if (a.type() != b.type()) {
        auto& integ  = a.isInt() ? a : b;
        auto& nonint = a.isInt() ? b : a;
        return Op<double>()(to<double>(integ.asInt()), nonint.asDouble());
      }
      if (a.isDouble()) {
        return Op<double>()(a.asDouble(), b.asDouble());
      }
      return Op<int64_t>()(a.asInt(), b.asInt());
    }
  
  }
  
  //////////////////////////////////////////////////////////////////////
  
  /*
   * We're doing this instead of a simple member typedef to avoid the
   * undefined behavior of parameterizing std::unordered_map<> with an
   * incomplete type.
   *
   * Note: Later we may add separate order tracking here (a multi-index
   * type of thing.)
   */
  struct dynamic::ObjectImpl : std::unordered_map<dynamic, dynamic> {};
  
  //////////////////////////////////////////////////////////////////////
  
  // Helper object for creating objects conveniently.  See object and
  // the dynamic::dynamic(ObjectMaker&&) ctor.
  struct dynamic::ObjectMaker {
    friend struct dynamic;
  
    explicit ObjectMaker() : val_(dynamic::object) {}
    explicit ObjectMaker(dynamic const& key, dynamic val)
      : val_(dynamic::object)
    {
      val_.insert(key, std::move(val));
    }
    explicit ObjectMaker(dynamic&& key, dynamic val)
      : val_(dynamic::object)
    {
      val_.insert(std::move(key), std::move(val));
    }
  
    // Make sure no one tries to save one of these into an lvalue with
    // auto or anything like that.
    ObjectMaker(ObjectMaker&&) = default;
    ObjectMaker(ObjectMaker const&) = delete;
    ObjectMaker& operator=(ObjectMaker const&) = delete;
    ObjectMaker& operator=(ObjectMaker&&) = delete;
  
    // These return rvalue-references instead of lvalue-references to allow
    // constructs like this to moved instead of copied:
    //  dynamic a = dynamic::object("a", "b")("c", "d")
    ObjectMaker&& operator()(dynamic const& key, dynamic val) {
      val_.insert(key, std::move(val));
      return std::move(*this);
    }
  
    ObjectMaker&& operator()(dynamic&& key, dynamic val) {
      val_.insert(std::move(key), std::move(val));
      return std::move(*this);
    }
  
  private:
    dynamic val_;
  };
  
  // This looks like a case for perfect forwarding, but our use of
  // std::initializer_list for constructing dynamic arrays makes it less
  // functional than doing this manually.
  inline dynamic::ObjectMaker dynamic::object() { return ObjectMaker(); }
  inline dynamic::ObjectMaker dynamic::object(dynamic&& a, dynamic&& b) {
    return ObjectMaker(std::move(a), std::move(b));
  }
  inline dynamic::ObjectMaker dynamic::object(dynamic const& a, dynamic&& b) {
    return ObjectMaker(a, std::move(b));
  }
  inline dynamic::ObjectMaker dynamic::object(dynamic&& a, dynamic const& b) {
    return ObjectMaker(std::move(a), b);
  }
  inline dynamic::ObjectMaker
  dynamic::object(dynamic const& a, dynamic const& b) {
    return ObjectMaker(a, b);
  }
  
  //////////////////////////////////////////////////////////////////////
  
  struct dynamic::const_item_iterator
    : boost::iterator_adaptor<dynamic::const_item_iterator,
                              dynamic::ObjectImpl::const_iterator> {
    /* implicit */ const_item_iterator(base_type b) : iterator_adaptor_(b) { }
  
   private:
    friend class boost::iterator_core_access;
  };
  
  struct dynamic::const_key_iterator
    : boost::iterator_adaptor<dynamic::const_key_iterator,
                              dynamic::ObjectImpl::const_iterator,
                              dynamic const> {
    /* implicit */ const_key_iterator(base_type b) : iterator_adaptor_(b) { }
  
   private:
    dynamic const& dereference() const {
      return base_reference()->first;
    }
    friend class boost::iterator_core_access;
  };
  
  struct dynamic::const_value_iterator
    : boost::iterator_adaptor<dynamic::const_value_iterator,
                              dynamic::ObjectImpl::const_iterator,
                              dynamic const> {
    /* implicit */ const_value_iterator(base_type b) : iterator_adaptor_(b) { }
  
   private:
    dynamic const& dereference() const {
      return base_reference()->second;
    }
    friend class boost::iterator_core_access;
  };
  
  //////////////////////////////////////////////////////////////////////
  
  inline dynamic::dynamic(ObjectMaker (*)())
    : type_(OBJECT)
  {
    new (getAddress<ObjectImpl>()) ObjectImpl();
  }
  
  inline dynamic::dynamic(StringPiece s)
    : type_(STRING)
  {
    new (&u_.string) fbstring(s.data(), s.size());
  }
  
  inline dynamic::dynamic(char const* s)
    : type_(STRING)
  {
    new (&u_.string) fbstring(s);
  }
  
  inline dynamic::dynamic(std::string const& s)
    : type_(STRING)
  {
    new (&u_.string) fbstring(s);
  }
  
  inline dynamic::dynamic(fbstring const& s)
    : type_(STRING)
  {
    new (&u_.string) fbstring(s);
  }
  
  inline dynamic::dynamic(fbstring&& s)
    : type_(STRING)
  {
    new (&u_.string) fbstring(std::move(s));
  }
  
  inline dynamic::dynamic(std::initializer_list<dynamic> il)
    : type_(ARRAY)
  {
    new (&u_.array) Array(il.begin(), il.end());
  }
  
  inline dynamic::dynamic(ObjectMaker&& maker)
    : type_(OBJECT)
  {
    new (getAddress<ObjectImpl>())
      ObjectImpl(std::move(*maker.val_.getAddress<ObjectImpl>()));
  }
  
  inline dynamic::dynamic(dynamic const& o)
    : type_(NULLT)
  {
    *this = o;
  }
  
  inline dynamic::dynamic(dynamic&& o)
    : type_(NULLT)
  {
    *this = std::move(o);
  }
  
  inline dynamic::~dynamic() { destroy(); }
  
  template<class T>
  dynamic::dynamic(T t) {
    typedef typename detail::ConversionHelper<T>::type U;
    type_ = TypeInfo<U>::type;
    new (getAddress<U>()) U(std::move(t));
  }
  
  template<class Iterator>
  dynamic::dynamic(Iterator first, Iterator last)
    : type_(ARRAY)
  {
    new (&u_.array) Array(first, last);
  }
  
  //////////////////////////////////////////////////////////////////////
  
  inline dynamic::const_iterator dynamic::begin() const {
    return get<Array>().begin();
  }
  inline dynamic::const_iterator dynamic::end() const {
    return get<Array>().end();
  }
  
  template <class It>
  struct dynamic::IterableProxy {
    typedef It const_iterator;
    typedef typename It::value_type value_type;
  
    /* implicit */ IterableProxy(const dynamic::ObjectImpl* o) : o_(o) { }
  
    It begin() const {
      return o_->begin();
    }
  
    It end() const {
      return o_->end();
    }
  
   private:
    const dynamic::ObjectImpl* o_;
  };
  
  inline dynamic::IterableProxy<dynamic::const_key_iterator> dynamic::keys()
    const {
    return &(get<ObjectImpl>());
  }
  
  inline dynamic::IterableProxy<dynamic::const_value_iterator> dynamic::values()
    const {
    return &(get<ObjectImpl>());
  }
  
  inline dynamic::IterableProxy<dynamic::const_item_iterator> dynamic::items()
    const {
    return &(get<ObjectImpl>());
  }
  
  inline bool dynamic::isString() const { return get_nothrow<fbstring>(); }
  inline bool dynamic::isObject() const { return get_nothrow<ObjectImpl>(); }
  inline bool dynamic::isBool()   const { return get_nothrow<bool>(); }
  inline bool dynamic::isArray()  const { return get_nothrow<Array>(); }
  inline bool dynamic::isDouble() const { return get_nothrow<double>(); }
  inline bool dynamic::isInt()    const { return get_nothrow<int64_t>(); }
  inline bool dynamic::isNull()   const { return get_nothrow<void*>(); }
  inline bool dynamic::isNumber() const { return isInt() || isDouble(); }
  
  inline dynamic::Type dynamic::type() const {
    return type_;
  }
  
  inline fbstring dynamic::asString() const { return asImpl<fbstring>(); }
  inline double   dynamic::asDouble() const { return asImpl<double>(); }
  inline int64_t  dynamic::asInt()    const { return asImpl<int64_t>(); }
  inline bool     dynamic::asBool()   const { return asImpl<bool>(); }
  
  inline const char* dynamic::data()  const { return get<fbstring>().data();  }
  inline const char* dynamic::c_str() const { return get<fbstring>().c_str(); }
  
  template<class T>
  struct dynamic::CompareOp {
    static bool comp(T const& a, T const& b) { return a < b; }
  };
  template<>
  struct dynamic::CompareOp<dynamic::ObjectImpl> {
    static bool comp(ObjectImpl const& a, ObjectImpl const& b) {
      // This code never executes; it is just here for the compiler.
      return false;
    }
  };
  
  inline bool dynamic::operator<(dynamic const& o) const {
    if (UNLIKELY(type_ == OBJECT || o.type_ == OBJECT)) {
      throw TypeError("object", type_);
    }
    if (type_ != o.type_) {
      return type_ < o.type_;
    }
  
  #define FB_X(T) return CompareOp<T>::comp(*getAddress<T>(),   \
                                            *o.getAddress<T>())
    FB_DYNAMIC_APPLY(type_, FB_X);
  #undef FB_X
  }
  
  inline bool dynamic::operator==(dynamic const& o) const {
    if (type() != o.type()) {
      if (isNumber() && o.isNumber()) {
        auto& integ = isInt() ? *this : o;
        auto& doubl = isInt() ? o     : *this;
        return integ.asInt() == doubl.asDouble();
      }
      return false;
    }
  
  #define FB_X(T) return *getAddress<T>() == *o.getAddress<T>();
    FB_DYNAMIC_APPLY(type_, FB_X);
  #undef FB_X
  }
  
  inline dynamic& dynamic::operator+=(dynamic const& o) {
    if (type() == STRING && o.type() == STRING) {
      *getAddress<fbstring>() += *o.getAddress<fbstring>();
      return *this;
    }
    *this = detail::numericOp<std::plus>(*this, o);
    return *this;
  }
  
  inline dynamic& dynamic::operator-=(dynamic const& o) {
    *this = detail::numericOp<std::minus>(*this, o);
    return *this;
  }
  
  inline dynamic& dynamic::operator*=(dynamic const& o) {
    *this = detail::numericOp<std::multiplies>(*this, o);
    return *this;
  }
  
  inline dynamic& dynamic::operator/=(dynamic const& o) {
    *this = detail::numericOp<std::divides>(*this, o);
    return *this;
  }
  
  #define FB_DYNAMIC_INTEGER_OP(op)                           \
    inline dynamic& dynamic::operator op(dynamic const& o) {  \
      if (!isInt() || !o.isInt()) {                           \
        throw TypeError("int64", type(), o.type());           \
      }                                                       \
      *getAddress<int64_t>() op o.asInt();                    \
      return *this;                                           \
    }
  
  FB_DYNAMIC_INTEGER_OP(%=)
  FB_DYNAMIC_INTEGER_OP(|=)
  FB_DYNAMIC_INTEGER_OP(&=)
  FB_DYNAMIC_INTEGER_OP(^=)
  
  #undef FB_DYNAMIC_INTEGER_OP
  
  inline dynamic& dynamic::operator++() {
    ++get<int64_t>();
    return *this;
  }
  
  inline dynamic& dynamic::operator--() {
    --get<int64_t>();
    return *this;
  }
  
  inline dynamic& dynamic::operator=(dynamic const& o) {
    if (&o != this) {
      destroy();
  #define FB_X(T) new (getAddress<T>()) T(*o.getAddress<T>())
      FB_DYNAMIC_APPLY(o.type_, FB_X);
  #undef FB_X
      type_ = o.type_;
    }
    return *this;
  }
  
  inline dynamic& dynamic::operator=(dynamic&& o) {
    if (&o != this) {
      destroy();
  #define FB_X(T) new (getAddress<T>()) T(std::move(*o.getAddress<T>()))
      FB_DYNAMIC_APPLY(o.type_, FB_X);
  #undef FB_X
      type_ = o.type_;
    }
    return *this;
  }
  
  inline dynamic& dynamic::operator[](dynamic const& k) {
    if (!isObject() && !isArray()) {
      throw TypeError("object/array", type());
    }
    if (isArray()) {
      return at(k);
    }
    auto& obj = get<ObjectImpl>();
    auto ret = obj.insert({k, nullptr});
    return ret.first->second;
  }
  
  inline dynamic const& dynamic::operator[](dynamic const& idx) const {
    return at(idx);
  }
  
  inline dynamic dynamic::getDefault(const dynamic& k, const dynamic& v) const {
    auto& obj = get<ObjectImpl>();
    auto it = obj.find(k);
    return it == obj.end() ? v : it->second;
  }
  
  inline dynamic&& dynamic::getDefault(const dynamic& k, dynamic&& v) const {
    auto& obj = get<ObjectImpl>();
    auto it = obj.find(k);
    if (it != obj.end()) {
      v = it->second;
    }
  
    return std::move(v);
  }
  
  template<class K, class V> inline dynamic& dynamic::setDefault(K&& k, V&& v) {
    auto& obj = get<ObjectImpl>();
    return obj.insert(std::make_pair(std::forward<K>(k),
                                     std::forward<V>(v))).first->second;
  }
  
  inline dynamic* dynamic::get_ptr(dynamic const& idx) {
    return const_cast<dynamic*>(const_cast<dynamic const*>(this)->get_ptr(idx));
  }
  
  inline const dynamic* dynamic::get_ptr(dynamic const& idx) const {
    if (auto* parray = get_nothrow<Array>()) {
      if (!idx.isInt()) {
        throw TypeError("int64", idx.type());
      }
      if (idx >= parray->size()) {
        return nullptr;
      }
      return &(*parray)[idx.asInt()];
    } else if (auto* pobject = get_nothrow<ObjectImpl>()) {
      auto it = pobject->find(idx);
      if (it == pobject->end()) {
        return nullptr;
      }
      return &it->second;
    } else {
      throw TypeError("object/array", type());
    }
  }
  
  inline dynamic& dynamic::at(dynamic const& idx) {
    return const_cast<dynamic&>(const_cast<dynamic const*>(this)->at(idx));
  }
  
  inline dynamic const& dynamic::at(dynamic const& idx) const {
    if (auto* parray = get_nothrow<Array>()) {
      if (!idx.isInt()) {
        throw TypeError("int64", idx.type());
      }
      if (idx >= parray->size()) {
        throw std::out_of_range("out of range in dynamic array");
      }
      return (*parray)[idx.asInt()];
    } else if (auto* pobject = get_nothrow<ObjectImpl>()) {
      auto it = pobject->find(idx);
      if (it == pobject->end()) {
        throw std::out_of_range(to<std::string>(
            "couldn't find key ", idx.asString(), " in dynamic object"));
      }
      return it->second;
    } else {
      throw TypeError("object/array", type());
    }
  }
  
  inline bool dynamic::empty() const {
    if (isNull()) {
      return true;
    }
    return !size();
  }
  
  inline std::size_t dynamic::size() const {
    if (auto* ar = get_nothrow<Array>()) {
      return ar->size();
    }
    if (auto* obj = get_nothrow<ObjectImpl>()) {
      return obj->size();
    }
    if (auto* str = get_nothrow<fbstring>()) {
      return str->size();
    }
    throw TypeError("array/object", type());
  }
  
  inline std::size_t dynamic::count(dynamic const& key) const {
    return find(key) != items().end();
  }
  
  inline dynamic::const_item_iterator dynamic::find(dynamic const& key) const {
    return get<ObjectImpl>().find(key);
  }
  
  template<class K, class V> inline void dynamic::insert(K&& key, V&& val) {
    auto& obj = get<ObjectImpl>();
    auto rv = obj.insert(std::make_pair(std::forward<K>(key),
                                        std::forward<V>(val)));
    if (!rv.second) {
      // note, the second use of std:forward<V>(val) is only correct
      // if the first one did not result in a move. obj[key] = val
      // would be preferrable but doesn't compile because dynamic
      // is (intentionally) not default constructable
      rv.first->second = std::forward<V>(val);
    }
  }
  
  inline std::size_t dynamic::erase(dynamic const& key) {
    auto& obj = get<ObjectImpl>();
    return obj.erase(key);
  }
  
  inline dynamic::const_iterator dynamic::erase(const_iterator it) {
    auto& arr = get<Array>();
    // std::vector doesn't have an erase method that works on const iterators,
    // even though the standard says it should, so this hack converts to a
    // non-const iterator before calling erase.
    return get<Array>().erase(arr.begin() + (it - arr.begin()));
  }
  
  inline dynamic::const_iterator
  dynamic::erase(const_iterator first, const_iterator last) {
    auto& arr = get<Array>();
    return get<Array>().erase(
      arr.begin() + (first - arr.begin()),
      arr.begin() + (last - arr.begin()));
  }
  
  inline dynamic::const_key_iterator dynamic::erase(const_key_iterator it) {
    return const_key_iterator(get<ObjectImpl>().erase(it.base()));
  }
  
  inline dynamic::const_key_iterator dynamic::erase(const_key_iterator first,
                                                    const_key_iterator last) {
    return const_key_iterator(get<ObjectImpl>().erase(first.base(),
                                                      last.base()));
  }
  
  inline dynamic::const_value_iterator dynamic::erase(const_value_iterator it) {
    return const_value_iterator(get<ObjectImpl>().erase(it.base()));
  }
  
  inline dynamic::const_value_iterator dynamic::erase(const_value_iterator first,
                                                      const_value_iterator last) {
    return const_value_iterator(get<ObjectImpl>().erase(first.base(),
                                                        last.base()));
  }
  
  inline dynamic::const_item_iterator dynamic::erase(const_item_iterator it) {
    return const_item_iterator(get<ObjectImpl>().erase(it.base()));
  }
  
  inline dynamic::const_item_iterator dynamic::erase(const_item_iterator first,
                                                     const_item_iterator last) {
    return const_item_iterator(get<ObjectImpl>().erase(first.base(),
                                                       last.base()));
  }
  
  inline void dynamic::resize(std::size_t sz, dynamic const& c) {
    auto& array = get<Array>();
    array.resize(sz, c);
  }
  
  inline void dynamic::push_back(dynamic const& v) {
    auto& array = get<Array>();
    array.push_back(v);
  }
  
  inline void dynamic::push_back(dynamic&& v) {
    auto& array = get<Array>();
    array.push_back(std::move(v));
  }
  
  inline void dynamic::pop_back() {
    auto& array = get<Array>();
    array.pop_back();
  }
  
  inline std::size_t dynamic::hash() const {
    switch (type()) {
    case OBJECT:
    case ARRAY:
    case NULLT:
      throw TypeError("not null/object/array", type());
    case INT64:
      return std::hash<int64_t>()(asInt());
    case DOUBLE:
      return std::hash<double>()(asDouble());
    case BOOL:
      return std::hash<bool>()(asBool());
    case STRING:
      return std::hash<fbstring>()(asString());
    default:
      CHECK(0); abort();
    }
  }
  
  //////////////////////////////////////////////////////////////////////
  
  template<class T> struct dynamic::TypeInfo {
    static char const name[];
    static Type const type;
  };
  
  #define FB_DEC_TYPE(T)                                      \
    template<> char const dynamic::TypeInfo<T>::name[];       \
    template<> dynamic::Type const dynamic::TypeInfo<T>::type
  
  FB_DEC_TYPE(void*);
  FB_DEC_TYPE(bool);
  FB_DEC_TYPE(fbstring);
  FB_DEC_TYPE(dynamic::Array);
  FB_DEC_TYPE(double);
  FB_DEC_TYPE(int64_t);
  FB_DEC_TYPE(dynamic::ObjectImpl);
  
  #undef FB_DEC_TYPE
  
  template<class T>
  T dynamic::asImpl() const {
    switch (type()) {
    case INT64:    return to<T>(*get_nothrow<int64_t>());
    case DOUBLE:   return to<T>(*get_nothrow<double>());
    case BOOL:     return to<T>(*get_nothrow<bool>());
    case STRING:   return to<T>(*get_nothrow<fbstring>());
    default:
      throw TypeError("int/double/bool/string", type());
    }
  }
  
  // Return a T* to our type, or null if we're not that type.
  template<class T>
  T* dynamic::get_nothrow() {
    if (type_ != TypeInfo<T>::type) {
      return nullptr;
    }
    return getAddress<T>();
  }
  
  template<class T>
  T const* dynamic::get_nothrow() const {
    return const_cast<dynamic*>(this)->get_nothrow<T>();
  }
  
  // Return T* for where we can put a T, without type checking.  (Memory
  // might be uninitialized, even.)
  template<class T>
  T* dynamic::getAddress() {
    return GetAddrImpl<T>::get(u_);
  }
  
  template<class T>
  T const* dynamic::getAddress() const {
    return const_cast<dynamic*>(this)->getAddress<T>();
  }
  
  template<class T> struct dynamic::GetAddrImpl {};
  template<> struct dynamic::GetAddrImpl<void*> {
    static void** get(Data& d) { return &d.nul; }
  };
  template<> struct dynamic::GetAddrImpl<dynamic::Array> {
    static Array* get(Data& d) { return &d.array; }
  };
  template<> struct dynamic::GetAddrImpl<bool> {
    static bool* get(Data& d) { return &d.boolean; }
  };
  template<> struct dynamic::GetAddrImpl<int64_t> {
    static int64_t* get(Data& d) { return &d.integer; }
  };
  template<> struct dynamic::GetAddrImpl<double> {
    static double* get(Data& d) { return &d.doubl; }
  };
  template<> struct dynamic::GetAddrImpl<fbstring> {
    static fbstring* get(Data& d) { return &d.string; }
  };
  template<> struct dynamic::GetAddrImpl<dynamic::ObjectImpl> {
    static_assert(sizeof(ObjectImpl) <= sizeof(Data::objectBuffer),
      "In your implementation, std::unordered_map<> apparently takes different"
      " amount of space depending on its template parameters.  This is "
      "weird.  Make objectBuffer bigger if you want to compile dynamic.");
  
    static ObjectImpl* get(Data& d) {
      void* data = &d.objectBuffer;
      return static_cast<ObjectImpl*>(data);
    }
  };
  
  template<class T>
  T& dynamic::get() {
    if (auto* p = get_nothrow<T>()) {
      return *p;
    }
    throw TypeError(TypeInfo<T>::name, type());
  }
  
  template<class T>
  T const& dynamic::get() const {
    return const_cast<dynamic*>(this)->get<T>();
  }
  
  inline char const* dynamic::typeName(Type t) {
  #define FB_X(T) return TypeInfo<T>::name
    FB_DYNAMIC_APPLY(t, FB_X);
  #undef FB_X
  }
  
  inline void dynamic::destroy() {
    // This short-circuit speeds up some microbenchmarks.
    if (type_ == NULLT) return;
  
  #define FB_X(T) detail::Destroy::destroy(getAddress<T>())
    FB_DYNAMIC_APPLY(type_, FB_X);
  #undef FB_X
    type_ = NULLT;
    u_.nul = nullptr;
  }
  
  //////////////////////////////////////////////////////////////////////
  
  /*
   * Helper for implementing operator<<.  Throws if the type shouldn't
   * support it.
   */
  template<class T>
  struct dynamic::PrintImpl {
    static void print(dynamic const&, std::ostream& out, T const& t) {
      out << t;
    }
  };
  template<>
  struct dynamic::PrintImpl<dynamic::ObjectImpl> {
    static void print(dynamic const& d,
                      std::ostream& out,
                      dynamic::ObjectImpl const&) {
      d.print_as_pseudo_json(out);
    }
  };
  template<>
  struct dynamic::PrintImpl<dynamic::Array> {
    static void print(dynamic const& d,
                      std::ostream& out,
                      dynamic::Array const&) {
      d.print_as_pseudo_json(out);
    }
  };
  
  inline void dynamic::print(std::ostream& out) const {
  #define FB_X(T) PrintImpl<T>::print(*this, out, *getAddress<T>())
    FB_DYNAMIC_APPLY(type_, FB_X);
  #undef FB_X
  }
  
  inline std::ostream& operator<<(std::ostream& out, dynamic const& d) {
    d.print(out);
    return out;
  }
  
  //////////////////////////////////////////////////////////////////////
  
  // Secialization of FormatValue so dynamic objects can be formatted
  template <>
  class FormatValue<dynamic> {
   public:
    explicit FormatValue(const dynamic& val) : val_(val) { }
  
    template <class FormatCallback>
    void format(FormatArg& arg, FormatCallback& cb) const {
      switch (val_.type()) {
      case dynamic::NULLT:
        FormatValue<std::nullptr_t>(nullptr).format(arg, cb);
        break;
      case dynamic::BOOL:
        FormatValue<bool>(val_.asBool()).format(arg, cb);
        break;
      case dynamic::INT64:
        FormatValue<int64_t>(val_.asInt()).format(arg, cb);
        break;
      case dynamic::STRING:
        FormatValue<fbstring>(val_.asString()).format(arg, cb);
        break;
      case dynamic::DOUBLE:
        FormatValue<double>(val_.asDouble()).format(arg, cb);
        break;
      case dynamic::ARRAY:
        FormatValue(val_.at(arg.splitIntKey())).format(arg, cb);
        break;
      case dynamic::OBJECT:
        FormatValue(val_.at(arg.splitKey().toFbstring())).format(arg, cb);
        break;
      }
    }
  
   private:
    const dynamic& val_;
  };
  
  template <class V>
  class FormatValue<detail::DefaultValueWrapper<dynamic, V>> {
   public:
    explicit FormatValue(
        const detail::DefaultValueWrapper<dynamic, V>& val)
      : val_(val) { }
  
    template <class FormatCallback>
    void format(FormatArg& arg, FormatCallback& cb) const {
      auto& c = val_.container;
      switch (c.type()) {
      case dynamic::NULLT:
      case dynamic::BOOL:
      case dynamic::INT64:
      case dynamic::STRING:
      case dynamic::DOUBLE:
        FormatValue<dynamic>(c).format(arg, cb);
        break;
      case dynamic::ARRAY:
        {
          int key = arg.splitIntKey();
          if (key >= 0 && key < c.size()) {
            FormatValue<dynamic>(c.at(key)).format(arg, cb);
          } else{
            FormatValue<V>(val_.defaultValue).format(arg, cb);
          }
        }
        break;
      case dynamic::OBJECT:
        {
          auto pos = c.find(arg.splitKey());
          if (pos != c.items().end()) {
            FormatValue<dynamic>(pos->second).format(arg, cb);
          } else {
            FormatValue<V>(val_.defaultValue).format(arg, cb);
          }
        }
        break;
      }
    }
  
   private:
    const detail::DefaultValueWrapper<dynamic, V>& val_;
  };
  
  }  // namespaces
  
  #undef FB_DYNAMIC_APPLY
  
  #endif
  