include/v8.h

// 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 V8_H_
#define V8_H_

#include <stddef.h>
#include <stdint.h>
#include <stdio.h>

#include "v8-version.h"
#include "v8config.h"

// We reserve the V8_* prefix for macros defined in V8 public API and
// assume there are no name conflicts with the embedder's code.

#ifdef V8_OS_WIN

// Setup for Windows DLL export/import. When building the V8 DLL the
// BUILDING_V8_SHARED needs to be defined. When building a program which uses
// the V8 DLL USING_V8_SHARED needs to be defined. When either building the V8
// static library or building a program which uses the V8 static library neither
// BUILDING_V8_SHARED nor USING_V8_SHARED should be defined.
#if defined(BUILDING_V8_SHARED) && defined(USING_V8_SHARED)
#error both BUILDING_V8_SHARED and USING_V8_SHARED are set - please check the\
  build configuration to ensure that at most one of these is set
#endif

#ifdef BUILDING_V8_SHARED
# define V8_EXPORT __declspec(dllexport)
#elif USING_V8_SHARED
# define V8_EXPORT __declspec(dllimport)
#else
# define V8_EXPORT
#endif  // BUILDING_V8_SHARED

#else  // V8_OS_WIN

// Setup for Linux shared library export.
#if V8_HAS_ATTRIBUTE_VISIBILITY && defined(V8_SHARED)
# ifdef BUILDING_V8_SHARED
#  define V8_EXPORT __attribute__ ((visibility("default")))
# else
#  define V8_EXPORT
# endif
#else
# define V8_EXPORT
#endif

#endif  // V8_OS_WIN

/**
 * The v8 JavaScript engine.
 */
namespace v8 {

class AccessorSignature;
class Array;
class Boolean;
class BooleanObject;
class Context;
class CpuProfiler;
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 Name;
class Number;
class NumberObject;
class Object;
class ObjectOperationDescriptor;
class ObjectTemplate;
class Platform;
class Primitive;
class Promise;
class RawOperationDescriptor;
class Script;
class SharedArrayBuffer;
class Signature;
class StartupData;
class StackFrame;
class StackTrace;
class String;
class StringObject;
class Symbol;
class SymbolObject;
class Uint32;
class Utils;
class Value;
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 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;
class Data;
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 Heap;
class HeapObject;
class Isolate;
class Object;
struct StreamedSource;
template<typename T> class CustomArguments;
class PropertyCallbackArguments;
class FunctionCallbackArguments;
class GlobalHandles;
}


/**
 * General purpose unique identifier.
 */
class UniqueId {
 public:
  explicit UniqueId(intptr_t data)
      : data_(data) {}

  bool operator==(const UniqueId& other) const {
    return data_ == other.data_;
  }

  bool operator!=(const UniqueId& other) const {
    return data_ != other.data_;
  }

  bool operator<(const UniqueId& other) const {
    return data_ < other.data_;
  }

 private:
  intptr_t data_;
};

// --- 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.  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_(0) {}
  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 Handle<String> to a
     * Handle<Number>.
     */
    TYPE_CHECK(T, S);
  }

  /**
   * Returns true if the handle is empty.
   */
  V8_INLINE bool IsEmpty() const { return val_ == 0; }

  /**
   * Sets the handle to be empty. IsEmpty() will then return true.
   */
  V8_INLINE void Clear() { val_ = 0; }

  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::Object** a = reinterpret_cast<internal::Object**>(this->val_);
    internal::Object** b = reinterpret_cast<internal::Object**>(that.val_);
    if (a == 0) return b == 0;
    if (b == 0) return false;
    return *a == *b;
  }

  template <class S> V8_INLINE bool operator==(
      const PersistentBase<S>& that) const {
    internal::Object** a = reinterpret_cast<internal::Object**>(this->val_);
    internal::Object** b = reinterpret_cast<internal::Object**>(that.val_);
    if (a == 0) return b == 0;
    if (b == 0) 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);
  }

  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));
  }


  template <class S> V8_INLINE Local<S> As() {
    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);

 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;
  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 S>
  V8_INLINE Local(S* that)
      : val_(that) {}
  V8_INLINE static Local<T> New(Isolate* isolate, T* that);
  T* val_;
};


// Handle is an alias for Local for historical reasons.
template <class T>
using Handle = Local<T>;


/**
 * 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; }

  template <class S>
  V8_WARN_UNUSED_RESULT V8_INLINE bool ToLocal(Local<S>* out) const {
    out->val_ = IsEmpty() ? nullptr : this->val_;
    return !IsEmpty();
  }

  // Will crash if the MaybeLocal<> is empty.
  V8_INLINE Local<T> ToLocalChecked();

  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 life of the isolate.
template <class T> class Eternal {
 public:
  V8_INLINE Eternal() : index_(kInitialValue) { }
  template<class S>
  V8_INLINE Eternal(Isolate* isolate, Local<S> handle) : index_(kInitialValue) {
    Set(isolate, handle);
  }
  // Can only be safely called if already set.
  V8_INLINE Local<T> Get(Isolate* isolate);
  V8_INLINE bool IsEmpty() { return index_ == kInitialValue; }
  template<class S> V8_INLINE void Set(Isolate* isolate, Local<S> handle);

 private:
  static const int kInitialValue = -1;
  int index_;
};


static const int kInternalFieldsInWeakCallback = 2;


template <typename T>
class WeakCallbackInfo {
 public:
  typedef void (*Callback)(const WeakCallbackInfo<T>& data);

  WeakCallbackInfo(Isolate* isolate, T* parameter,
                   void* internal_fields[kInternalFieldsInWeakCallback],
                   Callback* callback)
      : isolate_(isolate), parameter_(parameter), callback_(callback) {
    for (int i = 0; i < kInternalFieldsInWeakCallback; ++i) {
      internal_fields_[i] = internal_fields[i];
    }
  }

  V8_INLINE Isolate* GetIsolate() const { return isolate_; }
  V8_INLINE T* GetParameter() const { return parameter_; }
  V8_INLINE void* GetInternalField(int index) const;

  V8_INLINE V8_DEPRECATE_SOON("use indexed version",
                              void* GetInternalField1() const) {
    return internal_fields_[0];
  }
  V8_INLINE V8_DEPRECATE_SOON("use indexed version",
                              void* GetInternalField2() const) {
    return internal_fields_[1];
  }

  bool IsFirstPass() const { return callback_ != nullptr; }

  // 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* internal_fields_[kInternalFieldsInWeakCallback];
};


template <class T, class P>
class WeakCallbackData {
 public:
  typedef void (*Callback)(const WeakCallbackData<T, P>& data);

  WeakCallbackData(Isolate* isolate, P* parameter, Local<T> handle)
      : isolate_(isolate), parameter_(parameter), handle_(handle) {}

  V8_INLINE Isolate* GetIsolate() const { return isolate_; }
  V8_INLINE P* GetParameter() const { return parameter_; }
  V8_INLINE Local<T> GetValue() const { return handle_; }

 private:
  Isolate* isolate_;
  P* parameter_;
  Local<T> handle_;
};


// TODO(dcarney): delete this with WeakCallbackData
template <class T>
using PhantomCallbackData = WeakCallbackInfo<T>;


enum class WeakCallbackType { kParameter, kInternalFields };


/**
 * 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.
 *
 * 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 Handle<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_ == NULL; }
  V8_INLINE void Empty() { val_ = 0; }

  template <class S>
  V8_INLINE bool operator==(const PersistentBase<S>& that) const {
    internal::Object** a = reinterpret_cast<internal::Object**>(this->val_);
    internal::Object** b = reinterpret_cast<internal::Object**>(that.val_);
    if (a == NULL) return b == NULL;
    if (b == NULL) return false;
    return *a == *b;
  }

  template <class S> V8_INLINE bool operator==(const Handle<S>& that) const {
    internal::Object** a = reinterpret_cast<internal::Object**>(this->val_);
    internal::Object** b = reinterpret_cast<internal::Object**>(that.val_);
    if (a == NULL) return b == NULL;
    if (b == NULL) 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 Handle<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 V8_DEPRECATE_SOON(
      "use WeakCallbackInfo version",
      void SetWeak(P* parameter,
                   typename WeakCallbackData<T, P>::Callback callback));

  template <typename S, typename P>
  V8_INLINE V8_DEPRECATE_SOON(
      "use WeakCallbackInfo version",
      void SetWeak(P* parameter,
                   typename WeakCallbackData<S, P>::Callback callback));

  // Phantom persistents work like weak persistents, except that the pointer to
  // the object being collected is not available in the finalization callback.
  // This enables the garbage collector to collect the object and any objects
  // it references transitively in one GC cycle. At the moment you can either
  // specify a parameter for the callback or the location of two internal
  // fields in the dying object.
  template <typename P>
  V8_INLINE V8_DEPRECATE_SOON(
      "use SetWeak",
      void SetPhantom(P* parameter,
                      typename WeakCallbackInfo<P>::Callback callback,
                      int internal_field_index1 = -1,
                      int internal_field_index2 = -1));

  template <typename P>
  V8_INLINE void SetWeak(P* parameter,
                         typename WeakCallbackInfo<P>::Callback callback,
                         WeakCallbackType type);

  template<typename P>
  V8_INLINE P* ClearWeak();

  // TODO(dcarney): remove this.
  V8_INLINE void ClearWeak() { ClearWeak<void>(); }

  /**
   * Marks the reference to this object independent. Garbage collector is free
   * to ignore any object groups containing this object. Weak callback for an
   * independent handle should not assume that it will be preceded by a global
   * GC prologue callback or followed by a global GC epilogue callback.
   */
  V8_INLINE void MarkIndependent();

  /**
   * Marks the reference to this object partially dependent. Partially dependent
   * handles only depend on other partially dependent handles and these
   * dependencies are provided through object groups. It provides a way to build
   * smaller object groups for young objects that represent only a subset of all
   * external dependencies. This mark is automatically cleared after each
   * garbage collection.
   */
  V8_INLINE void MarkPartiallyDependent();

  V8_INLINE bool IsIndependent() const;

  /** Checks if the handle holds the only reference to an object. */
  V8_INLINE bool IsNearDeath() const;

  /** Returns true if the handle's reference is weak.  */
  V8_INLINE bool IsWeak() const;

  /**
   * Assigns a wrapper class ID to the handle. See RetainedObjectInfo interface
   * description in v8-profiler.h for details.
   */
  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;

 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) {}
  PersistentBase(PersistentBase& other) = delete;  // NOLINT
  void operator=(PersistentBase&) = delete;
  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 bevavior 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>(0) { }
  /**
   * Construct a Persistent from a Handle.
   * When the Handle 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, Handle<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>(0) {
    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) { // NOLINT
    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(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>&>(that);
  }

  // TODO(dcarney): this is pretty useless, fix or remove
  template <class S> V8_INLINE Persistent<S>& As() { // 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;

  template <class S> V8_INLINE Persistent(S* 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 Handle.
   * When the Handle 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, Handle<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) : PersistentBase<T>(other.val_) {
    other.val_ = nullptr;
  }
  V8_INLINE ~Global() { this->Reset(); }
  /**
   * Move via assignment.
   */
  template <class S>
  V8_INLINE Global& operator=(Global<S>&& rhs) {
    TYPE_CHECK(T, S);
    if (this != &rhs) {
      this->Reset();
      this->val_ = rhs.val_;
      rhs.val_ = nullptr;
    }
    return *this;
  }
  /**
   * Pass allows returning uniques from functions, etc.
   */
  Global Pass() { return static_cast<Global&&>(*this); }

  /*
   * For compatibility with Chromium's base::Bind (base::Passed).
   */
  typedef void MoveOnlyTypeForCPP03;

 private:
  template <class F>
  friend class ReturnValue;
  Global(Global&) = delete;
  void operator=(Global&) = delete;
  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 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:
  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_);
  }

 protected:
  V8_INLINE HandleScope() {}

  void Initialize(Isolate* isolate);

  static internal::Object** CreateHandle(internal::Isolate* isolate,
                                         internal::Object* value);

 private:
  // Uses heap_object to obtain the current Isolate.
  static internal::Object** CreateHandle(internal::HeapObject* heap_object,
                                         internal::Object* value);

  // Make it hard to create heap-allocated or illegal handle scopes by
  // disallowing certain operations.
  HandleScope(const HandleScope&);
  void operator=(const HandleScope&);
  void* operator new(size_t size);
  void operator delete(void*, size_t);

  internal::Isolate* isolate_;
  internal::Object** prev_next_;
  internal::Object** 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:
  EscapableHandleScope(Isolate* isolate);
  V8_INLINE ~EscapableHandleScope() {}

  /**
   * 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::Object** slot =
        Escape(reinterpret_cast<internal::Object**>(*value));
    return Local<T>(reinterpret_cast<T*>(slot));
  }

 private:
  internal::Object** Escape(internal::Object** escape_value);

  // Make it hard to create heap-allocated or illegal handle scopes by
  // disallowing certain operations.
  EscapableHandleScope(const EscapableHandleScope&);
  void operator=(const EscapableHandleScope&);
  void* operator new(size_t size);
  void operator delete(void*, size_t);

  internal::Object** escape_slot_;
};

class V8_EXPORT SealHandleScope {
 public:
  SealHandleScope(Isolate* isolate);
  ~SealHandleScope();

 private:
  // Make it hard to create heap-allocated or illegal handle scopes by
  // disallowing certain operations.
  SealHandleScope(const SealHandleScope&);
  void operator=(const SealHandleScope&);
  void* operator new(size_t size);
  void operator delete(void*, size_t);

  internal::Isolate* isolate_;
  int prev_level_;
  internal::Object** prev_limit_;
};


// --- Special objects ---


/**
 * The superclass of values and API object templates.
 */
class V8_EXPORT Data {
 private:
  Data();
};


/**
 * The optional attributes of ScriptOrigin.
 */
class ScriptOriginOptions {
 public:
  V8_INLINE ScriptOriginOptions(bool is_embedder_debug_script = false,
                                bool is_shared_cross_origin = false,
                                bool is_opaque = false)
      : flags_((is_embedder_debug_script ? kIsEmbedderDebugScript : 0) |
               (is_shared_cross_origin ? kIsSharedCrossOrigin : 0) |
               (is_opaque ? kIsOpaque : 0)) {}
  V8_INLINE ScriptOriginOptions(int flags)
      : flags_(flags &
               (kIsEmbedderDebugScript | kIsSharedCrossOrigin | kIsOpaque)) {}
  bool IsEmbedderDebugScript() const {
    return (flags_ & kIsEmbedderDebugScript) != 0;
  }
  bool IsSharedCrossOrigin() const {
    return (flags_ & kIsSharedCrossOrigin) != 0;
  }
  bool IsOpaque() const { return (flags_ & kIsOpaque) != 0; }
  int Flags() const { return flags_; }

 private:
  enum {
    kIsEmbedderDebugScript = 1,
    kIsSharedCrossOrigin = 1 << 1,
    kIsOpaque = 1 << 2
  };
  const int flags_;
};

/**
 * The origin, within a file, of a script.
 */
class ScriptOrigin {
 public:
  V8_INLINE ScriptOrigin(
      Handle<Value> resource_name,
      Handle<Integer> resource_line_offset = Handle<Integer>(),
      Handle<Integer> resource_column_offset = Handle<Integer>(),
      Handle<Boolean> resource_is_shared_cross_origin = Handle<Boolean>(),
      Handle<Integer> script_id = Handle<Integer>(),
      Handle<Boolean> resource_is_embedder_debug_script = Handle<Boolean>(),
      Handle<Value> source_map_url = Handle<Value>(),
      Handle<Boolean> resource_is_opaque = Handle<Boolean>());
  V8_INLINE Handle<Value> ResourceName() const;
  V8_INLINE Handle<Integer> ResourceLineOffset() const;
  V8_INLINE Handle<Integer> ResourceColumnOffset() const;
  /**
    * Returns true for embedder's debugger scripts
    */
  V8_INLINE Handle<Integer> ScriptID() const;
  V8_INLINE Handle<Value> SourceMapUrl() const;
  V8_INLINE ScriptOriginOptions Options() const { return options_; }

 private:
  Handle<Value> resource_name_;
  Handle<Integer> resource_line_offset_;
  Handle<Integer> resource_column_offset_;
  ScriptOriginOptions options_;
  Handle<Integer> script_id_;
  Handle<Value> source_map_url_;
};


/**
 * 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();
  Handle<Value> GetScriptName();

  /**
   * Data read from magic sourceURL comments.
   */
  Handle<Value> GetSourceURL();
  /**
   * Data read from magic sourceMappingURL comments.
   */
  Handle<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 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_DEPRECATE_SOON(
      "Use maybe version",
      Local<Script> Compile(Handle<String> source,
                            ScriptOrigin* origin = nullptr));
  static V8_WARN_UNUSED_RESULT MaybeLocal<Script> Compile(
      Local<Context> context, Handle<String> source,
      ScriptOrigin* origin = nullptr);

  static Local<Script> V8_DEPRECATE_SOON("Use maybe version",
                                         Compile(Handle<String> source,
                                                 Handle<String> file_name));

  /**
   * 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_DEPRECATE_SOON("Use maybe version", Local<Value> Run());
  V8_WARN_UNUSED_RESULT MaybeLocal<Value> Run(Local<Context> context);

  /**
   * Returns the corresponding context-unbound script.
   */
  Local<UnboundScript> GetUnboundScript();

  V8_DEPRECATED("Use GetUnboundScript()->GetId()",
                int GetId()) {
    return GetUnboundScript()->GetId();
  }
};


/**
 * 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(NULL),
          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;

   private:
    // Prevent copying. Not implemented.
    CachedData(const CachedData&);
    CachedData& operator=(const CachedData&);
  };

  /**
   * 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 = NULL);
    V8_INLINE Source(Local<String> source_string,
                     CachedData* cached_data = NULL);
    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;

   private:
    friend class ScriptCompiler;
    // Prevent copying. Not implemented.
    Source(const Source&);
    Source& operator=(const Source&);

    Local<String> source_string;

    // Origin information
    Handle<Value> resource_name;
    Handle<Integer> resource_line_offset;
    Handle<Integer> resource_column_offset;
    ScriptOriginOptions resource_options;
    Handle<Value> source_map_url;

    // 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() {}

    /**
     * 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.
     *
     * 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. It can be compiled after the streaming is complete.
   * StreamedSource must be kept alive while the streaming task is ran (see
   * ScriptStreamingTask below).
   */
  class V8_EXPORT StreamedSource {
   public:
    enum Encoding { ONE_BYTE, TWO_BYTE, UTF8 };

    StreamedSource(ExternalSourceStream* source_stream, Encoding encoding);
    ~StreamedSource();

    // Ownership of the CachedData or its buffers is *not* transferred to the
    // caller. The CachedData object is alive as long as the StreamedSource
    // object is alive.
    const CachedData* GetCachedData() const;

    internal::StreamedSource* impl() const { return impl_; }

   private:
    // Prevent copying. Not implemented.
    StreamedSource(const StreamedSource&);
    StreamedSource& operator=(const StreamedSource&);

    internal::StreamedSource* impl_;
  };

  /**
   * A streaming task which the embedder must run on a background thread to
   * stream scripts into V8. Returned by ScriptCompiler::StartStreamingScript.
   */
  class ScriptStreamingTask {
   public:
    virtual ~ScriptStreamingTask() {}
    virtual void Run() = 0;
  };

  enum CompileOptions {
    kNoCompileOptions = 0,
    kProduceParserCache,
    kConsumeParserCache,
    kProduceCodeCache,
    kConsumeCodeCache,

    // Support the previous API for a transition period.
    kProduceDataToCache
  };

  /**
   * 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_DEPRECATE_SOON("Use maybe version",
                           Local<UnboundScript> CompileUnbound(
                               Isolate* isolate, Source* source,
                               CompileOptions options = kNoCompileOptions));
  static V8_WARN_UNUSED_RESULT MaybeLocal<UnboundScript> CompileUnboundScript(
      Isolate* isolate, Source* source,
      CompileOptions options = kNoCompileOptions);

  /**
   * 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_DEPRECATE_SOON(
      "Use maybe version",
      Local<Script> Compile(Isolate* isolate, Source* source,
                            CompileOptions options = kNoCompileOptions));
  static V8_WARN_UNUSED_RESULT MaybeLocal<Script> Compile(
      Local<Context> context, Source* source,
      CompileOptions options = kNoCompileOptions);

  /**
   * 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_DEPRECATE_SOON(
      "Use maybe version",
      Local<Script> Compile(Isolate* isolate, StreamedSource* source,
                            Handle<String> full_source_string,
                            const ScriptOrigin& origin));
  static V8_WARN_UNUSED_RESULT MaybeLocal<Script> Compile(
      Local<Context> context, StreamedSource* source,
      Handle<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 currently compiler flags. This means 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 ES6 module.
   *
   * This is an experimental feature.
   *
   * TODO(adamk): Script is likely the wrong return value for this;
   * should return some new Module type.
   */
  static V8_DEPRECATE_SOON(
      "Use maybe version",
      Local<Script> CompileModule(Isolate* isolate, Source* source,
                                  CompileOptions options = kNoCompileOptions));
  static V8_WARN_UNUSED_RESULT MaybeLocal<Script> CompileModule(
      Local<Context> context, Source* source,
      CompileOptions options = kNoCompileOptions);

  /**
   * 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_DEPRECATE_SOON("Use maybe version",
                           Local<Function> CompileFunctionInContext(
                               Isolate* isolate, Source* source,
                               Local<Context> context, size_t arguments_count,
                               Local<String> arguments[],
                               size_t context_extension_count,
                               Local<Object> context_extensions[]));
  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[]);

 private:
  static V8_WARN_UNUSED_RESULT MaybeLocal<UnboundScript> CompileUnboundInternal(
      Isolate* isolate, Source* source, CompileOptions options, bool is_module);
};


/**
 * An error message.
 */
class V8_EXPORT Message {
 public:
  Local<String> Get() const;

  V8_DEPRECATE_SOON("Use maybe version", Local<String> GetSourceLine() 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.
   */
  Handle<Value> GetScriptResourceName() const;

  /**
   * Exception stack trace. By default stack traces are not captured for
   * uncaught exceptions. SetCaptureStackTraceForUncaughtExceptions allows
   * to change this option.
   */
  Handle<StackTrace> GetStackTrace() const;

  /**
   * Returns the number, 1-based, of the line where the error occurred.
   */
  V8_DEPRECATE_SOON("Use maybe version", int GetLineNumber() const);
  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 index within the line of the first character where
   * the error occurred.
   */
  V8_DEPRECATE_SOON("Use maybe version", 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.
   */
  V8_DEPRECATE_SOON("Use maybe version", 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.
   */
  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(uint32_t index) const;

  /**
   * Returns the number of StackFrames.
   */
  int GetFrameCount() const;

  /**
   * Returns StackTrace as a v8::Array that contains StackFrame objects.
   */
  Local<Array> AsArray();

  /**
   * 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 = kOverview);
};


/**
 * 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;
};


// A StateTag represents a possible state of the VM.
enum StateTag { JS, GC, COMPILER, OTHER, EXTERNAL, IDLE };


// A RegisterState represents the current state of registers used
// by the sampling profiler API.
struct RegisterState {
  RegisterState() : pc(NULL), sp(NULL), fp(NULL) {}
  void* pc;  // Instruction pointer.
  void* sp;  // Stack pointer.
  void* fp;  // Frame pointer.
};


// The output structure filled up by GetStackSample API function.
struct SampleInfo {
  size_t frames_count;
  StateTag vm_state;
};


/**
 * A JSON Parser.
 */
class V8_EXPORT JSON {
 public:
  /**
   * Tries to parse the string |json_string| and returns it as value if
   * successful.
   *
   * \param json_string The string to parse.
   * \return The corresponding value if successfully parsed.
   */
  static V8_DEPRECATE_SOON("Use maybe version",
                           Local<Value> Parse(Local<String> json_string));
  static V8_WARN_UNUSED_RESULT MaybeLocal<Value> Parse(
      Isolate* isolate, Local<String> json_string);
};


/**
 * A map whose keys are referenced weakly. It is similar to JavaScript WeakMap
 * but can be created without entering a v8::Context and hence shouldn't
 * escape to JavaScript.
 */
class V8_EXPORT NativeWeakMap : public Data {
 public:
  static Local<NativeWeakMap> New(Isolate* isolate);
  void Set(Handle<Value> key, Handle<Value> value);
  Local<Value> Get(Handle<Value> key);
  bool Has(Handle<Value> key);
  bool Delete(Handle<Value> key);
};


// --- 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 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.
   * This is an experimental feature.
   */
  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.
   * This is an experimental feature.
   */
  bool IsSymbol() const;

  /**
   * Returns true if this value is a function.
   */
  bool IsFunction() const;

  /**
   * Returns true if this value is an array.
   */
  bool IsArray() const;

  /**
   * Returns true if this value is an object.
   */
  bool IsObject() 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 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.
   * This is an experimental feature.
   */
  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 a Generator function.
   * This is an experimental feature.
   */
  bool IsGeneratorFunction() const;

  /**
   * Returns true if this value is a Generator object (iterator).
   * This is an experimental feature.
   */
  bool IsGeneratorObject() const;

  /**
   * Returns true if this value is a Promise.
   * This is an experimental feature.
   */
  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.
   * This is an experimental feature.
   */
  bool IsArrayBuffer() const;

  /**
   * Returns true if this value is an ArrayBufferView.
   * This is an experimental feature.
   */
  bool IsArrayBufferView() const;

  /**
   * Returns true if this value is one of TypedArrays.
   * This is an experimental feature.
   */
  bool IsTypedArray() const;

  /**
   * Returns true if this value is an Uint8Array.
   * This is an experimental feature.
   */
  bool IsUint8Array() const;

  /**
   * Returns true if this value is an Uint8ClampedArray.
   * This is an experimental feature.
   */
  bool IsUint8ClampedArray() const;

  /**
   * Returns true if this value is an Int8Array.
   * This is an experimental feature.
   */
  bool IsInt8Array() const;

  /**
   * Returns true if this value is an Uint16Array.
   * This is an experimental feature.
   */
  bool IsUint16Array() const;

  /**
   * Returns true if this value is an Int16Array.
   * This is an experimental feature.
   */
  bool IsInt16Array() const;

  /**
   * Returns true if this value is an Uint32Array.
   * This is an experimental feature.
   */
  bool IsUint32Array() const;

  /**
   * Returns true if this value is an Int32Array.
   * This is an experimental feature.
   */
  bool IsInt32Array() const;

  /**
   * Returns true if this value is a Float32Array.
   * This is an experimental feature.
   */
  bool IsFloat32Array() const;

  /**
   * Returns true if this value is a Float64Array.
   * This is an experimental feature.
   */
  bool IsFloat64Array() const;

  /**
   * Returns true if this value is a SIMD Float32x4.
   * This is an experimental feature.
   */
  bool IsFloat32x4() const;

  /**
   * Returns true if this value is a DataView.
   * This is an experimental feature.
   */
  bool IsDataView() const;

  /**
   * Returns true if this value is a SharedArrayBuffer.
   * This is an experimental feature.
   */
  bool IsSharedArrayBuffer() const;


  V8_WARN_UNUSED_RESULT MaybeLocal<Boolean> ToBoolean(
      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;

  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Boolean> ToBoolean(Isolate* isolate) const);
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Number> ToNumber(Isolate* isolate) const);
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<String> ToString(Isolate* isolate) const);
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<String> ToDetailString(Isolate* isolate) const);
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Object> ToObject(Isolate* isolate) const);
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Integer> ToInteger(Isolate* isolate) const);
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Uint32> ToUint32(Isolate* isolate) const);
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Int32> ToInt32(Isolate* isolate) const);

  inline V8_DEPRECATE_SOON("Use maybe version",
                           Local<Boolean> ToBoolean() const);
  inline V8_DEPRECATE_SOON("Use maybe version", Local<Number> ToNumber() const);
  inline V8_DEPRECATE_SOON("Use maybe version", Local<String> ToString() const);
  inline V8_DEPRECATE_SOON("Use maybe version",
                           Local<String> ToDetailString() const);
  inline V8_DEPRECATE_SOON("Use maybe version", Local<Object> ToObject() const);
  inline V8_DEPRECATE_SOON("Use maybe version",
                           Local<Integer> ToInteger() const);
  inline V8_DEPRECATE_SOON("Use maybe version", Local<Uint32> ToUint32() const);
  inline V8_DEPRECATE_SOON("Use maybe version", Local<Int32> ToInt32() const);

  /**
   * Attempts to convert a string to an array index.
   * Returns an empty handle if the conversion fails.
   */
  V8_DEPRECATE_SOON("Use maybe version", Local<Uint32> ToArrayIndex() const);
  V8_WARN_UNUSED_RESULT MaybeLocal<Uint32> ToArrayIndex(
      Local<Context> context) const;

  V8_WARN_UNUSED_RESULT Maybe<bool> BooleanValue(Local<Context> context) 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;

  V8_DEPRECATE_SOON("Use maybe version", bool BooleanValue() const);
  V8_DEPRECATE_SOON("Use maybe version", double NumberValue() const);
  V8_DEPRECATE_SOON("Use maybe version", int64_t IntegerValue() const);
  V8_DEPRECATE_SOON("Use maybe version", uint32_t Uint32Value() const);
  V8_DEPRECATE_SOON("Use maybe version", int32_t Int32Value() const);

  /** JS == */
  V8_DEPRECATE_SOON("Use maybe version", bool Equals(Handle<Value> that) const);
  V8_WARN_UNUSED_RESULT Maybe<bool> Equals(Local<Context> context,
                                           Handle<Value> that) const;
  bool StrictEquals(Handle<Value> that) const;
  bool SameValue(Handle<Value> that) const;

  template <class T> V8_INLINE static Value* Cast(T* value);

 private:
  V8_INLINE bool QuickIsUndefined() const;
  V8_INLINE bool QuickIsNull() 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 Handle<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(v8::Value* obj);
 private:
  static void CheckCast(v8::Value* obj);
};


enum class NewStringType { kNormal, kInternalized };


/**
 * A JavaScript string value (ECMA-262, 4.3.17).
 */
class V8_EXPORT String : public Name {
 public:
  static const int kMaxLength = (1 << 28) - 16;

  enum Encoding {
    UNKNOWN_ENCODING = 0x1,
    TWO_BYTE_ENCODING = 0x0,
    ONE_BYTE_ENCODING = 0x4
  };
  /**
   * Returns the number of characters in this string.
   */
  int Length() const;

  /**
   * Returns the number of bytes in the UTF-8 encoded
   * representation of this string.
   */
  int Utf8Length() const;

  /**
   * Returns whether this string is known to contain only one byte data.
   * Does not read the string.
   * False negatives are possible.
   */
  bool IsOneByte() const;

  /**
   * Returns whether this string contain only one byte data.
   * 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(uint16_t* buffer,
            int start = 0,
            int length = -1,
            int options = NO_OPTIONS) const;
  // One byte characters.
  int WriteOneByte(uint8_t* buffer,
                   int start = 0,
                   int length = -1,
                   int options = NO_OPTIONS) const;
  // UTF-8 encoded characters.
  int WriteUtf8(char* buffer,
                int length = -1,
                int* nchars_ref = NULL,
                int options = NO_OPTIONS) const;

  /**
   * A zero length string.
   */
  V8_INLINE static v8::Local<v8::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() {}

   protected:
    ExternalStringResourceBase() {}

    /**
     * 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; }

   private:
    // Disallow copying and assigning.
    ExternalStringResourceBase(const ExternalStringResourceBase&);
    void operator=(const ExternalStringResourceBase&);

    friend class v8::internal::Heap;
  };

  /**
   * 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.
     */
    virtual ~ExternalStringResource() {}

    /**
     * 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() {}
  };

  /**
   * 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.
     */
    virtual ~ExternalOneByteStringResource() {}
    /** 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() {}
  };

  /**
   * 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);

  // TODO(dcarney): remove with deprecation of New functions.
  enum NewStringType {
    kNormalString = static_cast<int>(v8::NewStringType::kNormal),
    kInternalizedString = static_cast<int>(v8::NewStringType::kInternalized)
  };

  /** Allocates a new string from UTF-8 data.*/
  static V8_DEPRECATE_SOON(
      "Use maybe version",
      Local<String> NewFromUtf8(Isolate* isolate, const char* data,
                                NewStringType type = kNormalString,
                                int length = -1));

  /** 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, v8::NewStringType type,
      int length = -1);

  /** Allocates a new string from Latin-1 data.*/
  static V8_DEPRECATE_SOON(
      "Use maybe version",
      Local<String> NewFromOneByte(Isolate* isolate, const uint8_t* data,
                                   NewStringType type = kNormalString,
                                   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, v8::NewStringType type,
      int length = -1);

  /** Allocates a new string from UTF-16 data.*/
  static V8_DEPRECATE_SOON(
      "Use maybe version",
      Local<String> NewFromTwoByte(Isolate* isolate, const uint16_t* data,
                                   NewStringType type = kNormalString,
                                   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, v8::NewStringType type,
      int length = -1);

  /**
   * Creates a new string by concatenating the left and the right strings
   * passed in as parameters.
   */
  static Local<String> Concat(Handle<String> left, Handle<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_DEPRECATE_SOON(
      "Use maybe version",
      Local<String> NewExternal(Isolate* isolate,
                                ExternalStringResource* 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_DEPRECATE_SOON(
      "Use maybe version",
      Local<String> NewExternal(Isolate* isolate,
                                ExternalOneByteStringResource* 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();

  /**
   * 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:
    explicit Utf8Value(Handle<v8::Value> obj);
    ~Utf8Value();
    char* operator*() { return str_; }
    const char* operator*() const { return str_; }
    int length() const { return length_; }
   private:
    char* str_;
    int length_;

    // Disallow copying and assigning.
    Utf8Value(const Utf8Value&);
    void operator=(const Utf8Value&);
  };

  /**
   * Converts an object to a two-byte 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:
    explicit Value(Handle<v8::Value> obj);
    ~Value();
    uint16_t* operator*() { return str_; }
    const uint16_t* operator*() const { return str_; }
    int length() const { return length_; }
   private:
    uint16_t* str_;
    int length_;

    // Disallow copying and assigning.
    Value(const Value&);
    void operator=(const Value&);
  };

 private:
  void VerifyExternalStringResourceBase(ExternalStringResourceBase* v,
                                        Encoding encoding) const;
  void VerifyExternalStringResource(ExternalStringResource* val) const;
  static void CheckCast(v8::Value* obj);
};


/**
 * A JavaScript symbol (ECMA-262 edition 6)
 *
 * This is an experimental feature. Use at your own risk.
 */
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> GetIterator(Isolate* isolate);
  static Local<Symbol> GetUnscopables(Isolate* isolate);
  static Local<Symbol> GetToStringTag(Isolate* isolate);

  V8_INLINE static Symbol* Cast(v8::Value* obj);

 private:
  Symbol();
  static void CheckCast(v8::Value* obj);
};


/**
 * 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);
};


enum PropertyAttribute {
  None       = 0,
  ReadOnly   = 1 << 0,
  DontEnum   = 1 << 1,
  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
};


/**
 * A JavaScript object (ECMA-262, 4.3.3)
 */
class V8_EXPORT Object : public Value {
 public:
  V8_DEPRECATE_SOON("Use maybe version",
                    bool Set(Handle<Value> key, Handle<Value> value));
  V8_WARN_UNUSED_RESULT Maybe<bool> Set(Local<Context> context,
                                        Local<Value> key, Local<Value> value);

  V8_DEPRECATE_SOON("Use maybe version",
                    bool Set(uint32_t index, Handle<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);

  // Sets an own property on this object bypassing interceptors and
  // overriding accessors or read-only properties.
  //
  // Note that if the object has an interceptor the property will be set
  // locally, but since the interceptor takes precedence the local property
  // will only be returned if the interceptor doesn't return a value.
  //
  // Note also that this only works for named properties.
  V8_DEPRECATE_SOON("Use CreateDataProperty",
                    bool ForceSet(Handle<Value> key, Handle<Value> value,
                                  PropertyAttribute attribs = None));
  V8_DEPRECATE_SOON("Use CreateDataProperty",
                    Maybe<bool> ForceSet(Local<Context> context,
                                         Local<Value> key, Local<Value> value,
                                         PropertyAttribute attribs = None));

  V8_DEPRECATE_SOON("Use maybe version", Local<Value> Get(Handle<Value> key));
  V8_WARN_UNUSED_RESULT MaybeLocal<Value> Get(Local<Context> context,
                                              Local<Value> key);

  V8_DEPRECATE_SOON("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_DEPRECATE_SOON("Use maybe version",
                    PropertyAttribute GetPropertyAttributes(Handle<Value> key));
  V8_WARN_UNUSED_RESULT Maybe<PropertyAttribute> GetPropertyAttributes(
      Local<Context> context, Local<Value> key);

  /**
   * Returns Object.getOwnPropertyDescriptor as per ES5 section 15.2.3.3.
   */
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Value> GetOwnPropertyDescriptor(Local<String> key));
  V8_WARN_UNUSED_RESULT MaybeLocal<Value> GetOwnPropertyDescriptor(
      Local<Context> context, Local<String> key);

  V8_DEPRECATE_SOON("Use maybe version", bool Has(Handle<Value> key));
  V8_WARN_UNUSED_RESULT Maybe<bool> Has(Local<Context> context,
                                        Local<Value> key);

  V8_DEPRECATE_SOON("Use maybe version", bool Delete(Handle<Value> key));
  // TODO(dcarney): mark V8_WARN_UNUSED_RESULT
  Maybe<bool> Delete(Local<Context> context, Local<Value> key);

  V8_DEPRECATE_SOON("Use maybe version", bool Has(uint32_t index));
  V8_WARN_UNUSED_RESULT Maybe<bool> Has(Local<Context> context, uint32_t index);

  V8_DEPRECATE_SOON("Use maybe version", bool Delete(uint32_t index));
  // TODO(dcarney): mark V8_WARN_UNUSED_RESULT
  Maybe<bool> Delete(Local<Context> context, uint32_t index);

  V8_DEPRECATE_SOON("Use maybe version",
                    bool SetAccessor(Handle<String> name,
                                     AccessorGetterCallback getter,
                                     AccessorSetterCallback setter = 0,
                                     Handle<Value> data = Handle<Value>(),
                                     AccessControl settings = DEFAULT,
                                     PropertyAttribute attribute = None));
  V8_DEPRECATE_SOON("Use maybe version",
                    bool SetAccessor(Handle<Name> name,
                                     AccessorNameGetterCallback getter,
                                     AccessorNameSetterCallback setter = 0,
                                     Handle<Value> data = Handle<Value>(),
                                     AccessControl settings = DEFAULT,
                                     PropertyAttribute attribute = None));
  // TODO(dcarney): mark V8_WARN_UNUSED_RESULT
  Maybe<bool> SetAccessor(Local<Context> context, Local<Name> name,
                          AccessorNameGetterCallback getter,
                          AccessorNameSetterCallback setter = 0,
                          MaybeLocal<Value> data = MaybeLocal<Value>(),
                          AccessControl settings = DEFAULT,
                          PropertyAttribute attribute = None);

  void SetAccessorProperty(Local<Name> name,
                           Local<Function> getter,
                           Handle<Function> setter = Handle<Function>(),
                           PropertyAttribute attribute = None,
                           AccessControl settings = DEFAULT);

  /**
   * 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_DEPRECATE_SOON("Use maybe version", Local<Array> GetPropertyNames());
  V8_WARN_UNUSED_RESULT MaybeLocal<Array> GetPropertyNames(
      Local<Context> context);

  /**
   * This function has the same functionality as GetPropertyNames but
   * the returned array doesn't contain the names of properties from
   * prototype objects.
   */
  V8_DEPRECATE_SOON("Use maybe version", Local<Array> GetOwnPropertyNames());
  V8_WARN_UNUSED_RESULT MaybeLocal<Array> GetOwnPropertyNames(
      Local<Context> context);

  /**
   * 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_DEPRECATE_SOON("Use maybe version",
                    bool SetPrototype(Handle<Value> prototype));
  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(Handle<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_DEPRECATE_SOON("Use maybe version", Local<String> ObjectProtoToString());
  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();

  /** Gets the number of internal fields for this Object. */
  int InternalFieldCount();

  /** Same as above, but works for Persistents */
  V8_INLINE static int InternalFieldCount(
      const PersistentBase<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, Handle<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 Persistents */
  V8_INLINE static void* GetAlignedPointerFromInternalField(
      const PersistentBase<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);

  // Testers for local properties.
  V8_DEPRECATE_SOON("Use maybe version",
                    bool HasOwnProperty(Handle<String> key));
  V8_WARN_UNUSED_RESULT Maybe<bool> HasOwnProperty(Local<Context> context,
                                                   Local<Name> key);
  V8_DEPRECATE_SOON("Use maybe version",
                    bool HasRealNamedProperty(Handle<String> key));
  V8_WARN_UNUSED_RESULT Maybe<bool> HasRealNamedProperty(Local<Context> context,
                                                         Local<Name> key);
  V8_DEPRECATE_SOON("Use maybe version",
                    bool HasRealIndexedProperty(uint32_t index));
  V8_WARN_UNUSED_RESULT Maybe<bool> HasRealIndexedProperty(
      Local<Context> context, uint32_t index);
  V8_DEPRECATE_SOON("Use maybe version",
                    bool HasRealNamedCallbackProperty(Handle<String> key));
  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_DEPRECATE_SOON(
      "Use maybe version",
      Local<Value> GetRealNamedPropertyInPrototypeChain(Handle<String> key));
  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_DEPRECATE_SOON(
      "Use maybe version",
      Maybe<PropertyAttribute> GetRealNamedPropertyAttributesInPrototypeChain(
          Handle<String> key));
  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_DEPRECATE_SOON("Use maybe version",
                    Local<Value> GetRealNamedProperty(Handle<String> key));
  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_DEPRECATE_SOON("Use maybe version",
                    Maybe<PropertyAttribute> GetRealNamedPropertyAttributes(
                        Handle<String> key));
  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();

  /**
   * Turns on access check on the object if the object is an instance of
   * a template that has access check callbacks. If an object has no
   * access check info, the object cannot be accessed by anyone.
   */
  V8_DEPRECATE_SOON("No alternative", void TurnOnAccessCheck());

  /**
   * 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();

  /**
   * Access hidden properties on JavaScript objects. These properties are
   * hidden from the executing JavaScript and only accessible through the V8
   * C++ API. Hidden properties introduced by V8 internally (for example the
   * identity hash) are prefixed with "v8::".
   */
  // TODO(dcarney): convert these to take a isolate and optionally bailout?
  bool SetHiddenValue(Handle<String> key, Handle<Value> value);
  Local<Value> GetHiddenValue(Handle<String> key);
  bool DeleteHiddenValue(Handle<String> key);

  /**
   * 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();

  /**
   * Checks whether a callback is set by the
   * ObjectTemplate::SetCallAsFunctionHandler method.
   * When an Object is callable this method returns true.
   */
  bool IsCallable();

  /**
   * Call an Object as a function if a callback is set by the
   * ObjectTemplate::SetCallAsFunctionHandler method.
   */
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Value> CallAsFunction(Handle<Value> recv, int argc,
                                                Handle<Value> argv[]));
  V8_WARN_UNUSED_RESULT MaybeLocal<Value> CallAsFunction(Local<Context> context,
                                                         Handle<Value> recv,
                                                         int argc,
                                                         Handle<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_DEPRECATE_SOON("Use maybe version",
                    Local<Value> CallAsConstructor(int argc,
                                                   Handle<Value> argv[]));
  V8_WARN_UNUSED_RESULT MaybeLocal<Value> CallAsConstructor(
      Local<Context> context, int argc, Local<Value> argv[]);

  /**
   * Return the isolate to which the Object belongs to.
   */
  V8_DEPRECATE_SOON("Keep track of isolate correctly", Isolate* GetIsolate());

  static Local<Object> New(Isolate* isolate);

  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;

  /**
   * Clones an element at index |index|.  Returns an empty
   * handle if cloning fails (for any reason).
   */
  V8_DEPRECATE_SOON("Use maybe version",
                    Local<Object> CloneElementAt(uint32_t index));
  V8_WARN_UNUSED_RESULT MaybeLocal<Object> CloneElementAt(
      Local<Context> context, uint32_t index);

  /**
   * 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);

  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;

  /**
   * 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);

  /**
   * Creates a new Map containing the elements of array, which must be formatted
   * in the same manner as the array returned from AsArray().
   * Guaranteed to be side-effect free if the array contains no holes.
   */
  static V8_WARN_UNUSED_RESULT MaybeLocal<Map> FromArray(Local<Context> context,
                                                         Local<Array> array);

  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;

  /**
   * Returns an array of the keys in this Set.
   */
  Local<Array> AsArray() const;

  /**
   * Creates a new empty Set.
   */
  static Local<Set> New(Isolate* isolate);

  /**
   * Creates a new Set containing the items in array.
   * Guaranteed to be side-effect free if the array contains no holes.
   */
  static V8_WARN_UNUSED_RESULT MaybeLocal<Set> FromArray(Local<Context> context,
                                                         Local<Array> array);

  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);
  }
  // Handle setters
  template <typename S>
  V8_INLINE V8_DEPRECATE_SOON("Use Global<> instead",
                              void Set(const Persistent<S>& handle));
  template <typename S>
  V8_INLINE void Set(const Global<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();

  // Pointer setter: Uncompilable to prevent inadvertent misuse.
  template <typename S>
  V8_INLINE void Set(S* whatever);

 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::Object* value) { *value_ = value; }
  V8_INLINE internal::Object* GetDefaultValue();
  V8_INLINE explicit ReturnValue(internal::Object** slot);
  internal::Object** 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:
  V8_INLINE int Length() const;
  V8_INLINE Local<Value> operator[](int i) const;
  V8_INLINE Local<Function> Callee() const;
  V8_INLINE Local<Object> This() const;
  V8_INLINE Local<Object> Holder() const;
  V8_INLINE bool IsConstructCall() const;
  V8_INLINE Local<Value> Data() const;
  V8_INLINE Isolate* GetIsolate() const;
  V8_INLINE ReturnValue<T> GetReturnValue() const;
  // This shouldn't be public, but the arm compiler needs it.
  static const int kArgsLength = 7;

 protected:
  friend class internal::FunctionCallbackArguments;
  friend class internal::CustomArguments<FunctionCallbackInfo>;
  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 kCalleeIndex = 5;
  static const int kContextSaveIndex = 6;

  V8_INLINE FunctionCallbackInfo(internal::Object** implicit_args,
                   internal::Object** values,
                   int length,
                   bool is_construct_call);
  internal::Object** implicit_args_;
  internal::Object** values_;
  int length_;
  int is_construct_call_;
};


/**
 * The information passed to a property callback about the context
 * of the property access.
 */
template<typename T>
class PropertyCallbackInfo {
 public:
  V8_INLINE Isolate* GetIsolate() const;
  V8_INLINE Local<Value> Data() const;
  V8_INLINE Local<Object> This() const;
  V8_INLINE Local<Object> Holder() const;
  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 MacroAssembler;
  friend class internal::PropertyCallbackArguments;
  friend class internal::CustomArguments<PropertyCallbackInfo>;
  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