v8/src/arguments.h

// Copyright 2006-2008 the V8 project authors. All rights reserved.
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#ifndef V8_ARGUMENTS_H_
#define V8_ARGUMENTS_H_

namespace v8 {
namespace internal {

// Arguments provides access to runtime call parameters.
//
// It uses the fact that the instance fields of Arguments
// (length_, arguments_) are "overlayed" with the parameters
// (no. of parameters, and the parameter pointer) passed so
// that inside the C++ function, the parameters passed can
// be accessed conveniently:
//
//   Object* Runtime_function(Arguments args) {
//     ... use args[i] here ...
//   }

class Arguments BASE_EMBEDDED {
 public:
  Arguments(int length, Object** arguments)
      : length_(length), arguments_(arguments) { }

  Object*& operator[] (int index) {
    ASSERT(0 <= index && index < length_);
    return arguments_[-index];
  }

  template <class S> Handle<S> at(int index) {
    Object** value = &((*this)[index]);
    // This cast checks that the object we're accessing does indeed have the
    // expected type.
    S::cast(*value);
    return Handle<S>(reinterpret_cast<S**>(value));
  }

  // Get the total number of arguments including the receiver.
  int length() const { return length_; }

  Object** arguments() { return arguments_; }

 private:
  int length_;
  Object** arguments_;
};


// Custom arguments replicate a small segment of stack that can be
// accessed through an Arguments object the same way the actual stack
// can.
class CustomArguments : public Relocatable {
 public:
  inline CustomArguments(Object* data,
                         JSObject* self,
                         JSObject* holder) {
    values_[2] = self;
    values_[1] = holder;
    values_[0] = data;
  }

  inline CustomArguments() {
#ifdef DEBUG
    for (size_t i = 0; i < ARRAY_SIZE(values_); i++) {
      values_[i] = reinterpret_cast<Object*>(kZapValue);
    }
#endif
  }

  void IterateInstance(ObjectVisitor* v);
  Object** end() { return values_ + ARRAY_SIZE(values_) - 1; }
 private:
  Object* values_[3];
};


} }  // namespace v8::internal

#endif  // V8_ARGUMENTS_H_