✏ EDIT: node_object_wrap.h

// Copyright Joyent, Inc. and other Node contributors.
//
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// following conditions:
//
// The above copyright notice and this permission notice shall be included
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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#ifndef SRC_NODE_OBJECT_WRAP_H_
#define SRC_NODE_OBJECT_WRAP_H_

#include "v8.h"
#include <assert.h>

namespace node {

class ObjectWrap {
 public:
  ObjectWrap() {
    refs_ = 0;
  }

virtual ~ObjectWrap() {
    if (persistent().IsEmpty())
      return;
    persistent().ClearWeak();
    persistent().Reset();
  }

template <class T>
  static inline T* Unwrap(v8::Local<v8::Object> handle) {
    assert(!handle.IsEmpty());
    assert(handle->InternalFieldCount() > 0);
    // Cast to ObjectWrap before casting to T.  A direct cast from void
    // to T won't work right when T has more than one base class.
    void* ptr = handle->GetAlignedPointerFromInternalField(0);
    ObjectWrap* wrap = static_cast<ObjectWrap*>(ptr);
    return static_cast<T*>(wrap);
  }

inline v8::Local<v8::Object> handle() {
    return handle(v8::Isolate::GetCurrent());
  }

inline v8::Local<v8::Object> handle(v8::Isolate* isolate) {
    return v8::Local<v8::Object>::New(isolate, persistent());
  }

inline v8::Persistent<v8::Object>& persistent() {
    return handle_;
  }

protected:
  inline void Wrap(v8::Local<v8::Object> handle) {
    assert(persistent().IsEmpty());
    assert(handle->InternalFieldCount() > 0);
    handle->SetAlignedPointerInInternalField(0, this);
    persistent().Reset(v8::Isolate::GetCurrent(), handle);
    MakeWeak();
  }

inline void MakeWeak(void) {
    persistent().SetWeak(this, WeakCallback, v8::WeakCallbackType::kParameter);
  }

/* Ref() marks the object as being attached to an event loop.
   * Refed objects will not be garbage collected, even if
   * all references are lost.
   */
  virtual void Ref() {
    assert(!persistent().IsEmpty());
    persistent().ClearWeak();
    refs_++;
  }

/* Unref() marks an object as detached from the event loop.  This is its
   * default state.  When an object with a "weak" reference changes from
   * attached to detached state it will be freed. Be careful not to access
   * the object after making this call as it might be gone!
   * (A "weak reference" means an object that only has a
   * persistent handle.)
   *
   * DO NOT CALL THIS FROM DESTRUCTOR
   */
  virtual void Unref() {
    assert(!persistent().IsEmpty());
    assert(!persistent().IsWeak());
    assert(refs_ > 0);
    if (--refs_ == 0)
      MakeWeak();
  }

int refs_;  // ro

private:
  static void WeakCallback(
      const v8::WeakCallbackInfo<ObjectWrap>& data) {
    ObjectWrap* wrap = data.GetParameter();
    assert(wrap->refs_ == 0);
    wrap->handle_.Reset();
    delete wrap;
  }

v8::Persistent<v8::Object> handle_;
};

}  // namespace node

#endif  // SRC_NODE_OBJECT_WRAP_H_

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