add a default value for return value

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2834 matching lines @@
   // Fast JS primitive setters
   V8_INLINE(void SetNull());
   V8_INLINE(void SetUndefined());
   // Convenience getter for Isolate
   V8_INLINE(Isolate* GetIsolate());
 
  private:
   template<class F> friend class ReturnValue;
   template<class F> friend class FunctionCallbackInfo;
   template<class F> friend class PropertyCallbackInfo;
+  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 = 5;
+  static const int kArgsLength = 6;
 
  protected:
   friend class internal::FunctionCallbackArguments;
   friend class internal::CustomArguments<FunctionCallbackInfo>;
   static const int kReturnValueIndex = 0;
-  static const int kIsolateIndex = -1;
-  static const int kDataIndex = -2;
-  static const int kCalleeIndex = -3;
-  static const int kHolderIndex = -4;
+  static const int kReturnValueDefaultValueIndex = -1;
+  static const int kIsolateIndex = -2;
+  static const int kDataIndex = -3;
+  static const int kCalleeIndex = -4;
+  static const int kHolderIndex = -5;
 
   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_;
   bool is_construct_call_;
 };
@@ skipping 14 matching lines @@
  */
 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 = 5;
+  static const int kArgsLength = 6;
 
  protected:
   friend class MacroAssembler;
   friend class internal::PropertyCallbackArguments;
   friend class internal::CustomArguments<PropertyCallbackInfo>;
   static const int kThisIndex = 0;
   static const int kHolderIndex = -1;
   static const int kDataIndex = -2;
   static const int kReturnValueIndex = -3;
-  static const int kIsolateIndex = -4;
+  static const int kReturnValueDefaultValueIndex = -4;
+  static const int kIsolateIndex = -5;
 
   V8_INLINE(PropertyCallbackInfo(internal::Object** args))
       : args_(args) { }
   internal::Object** args_;
 };
 
 
 class V8EXPORT AccessorInfo : public PropertyCallbackInfo<Value> {
  private:
   friend class internal::PropertyCallbackArguments;
@@ skipping 2707 matching lines @@
 
 
 template<typename T>
 ReturnValue<T>::ReturnValue(internal::Object** slot) : value_(slot) {}
 
 template<typename T>
 template<typename S>
 void ReturnValue<T>::Set(const Persistent<S>& handle) {
   TYPE_CHECK(T, S);
   if (V8_UNLIKELY(handle.IsEmpty())) {
-    SetUndefined();
+    *value_ = GetDefaultValue();
   } else {
     *value_ = *reinterpret_cast<internal::Object**>(*handle);
   }
 }
 
 template<typename T>
 template<typename S>
 void ReturnValue<T>::Set(const Handle<S> handle) {
   TYPE_CHECK(T, S);
   if (V8_UNLIKELY(handle.IsEmpty())) {
-    SetUndefined();
+    *value_ = GetDefaultValue();
   } else {
     *value_ = *reinterpret_cast<internal::Object**>(*handle);
   }
 }
 
 template<typename T>
 void ReturnValue<T>::Set(double i) {
   Set(Number::New(GetIsolate(), i));
 }
 
@@ skipping 38 matching lines @@
 }
 
 template<typename T>
 void ReturnValue<T>::SetUndefined() {
   typedef internal::Internals I;
   *value_ = *I::GetRoot(GetIsolate(), I::kUndefinedValueRootIndex);
 }
 
 template<typename T>
 Isolate* ReturnValue<T>::GetIsolate() {
-  // Isolate is always the pointer below value_ on the stack.
-  return *reinterpret_cast<Isolate**>(&value_[-1]);
+  // Isolate is always the pointer below the default value on the stack.
+  return *reinterpret_cast<Isolate**>(&value_[-2]);
+}
+
+template<typename T>
+internal::Object* ReturnValue<T>::GetDefaultValue() {
+  // Default value is always the pointer below value_ on the stack.
+  return value_[-1];
 }
 
 
 template<typename T>
 FunctionCallbackInfo<T>::FunctionCallbackInfo(internal::Object** implicit_args,
                                               internal::Object** values,
                                               int length,
                                               bool is_construct_call)
     : implicit_args_(implicit_args),
       values_(values),
@@ skipping 575 matching lines @@
 
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_