prototype.h

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// Copyright 2014 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.
 
#ifndef V8_PROTOTYPE_H_
#define V8_PROTOTYPE_H_
 
#include "src/isolate.h"
#include "src/objects.h"
 
namespace v8 {
namespace internal {
 
/**
 * A class to uniformly access the prototype of any Object and walk its
 * prototype chain.
 *
 * The PrototypeIterator can either start at the prototype (default), or
 * include the receiver itself. If a PrototypeIterator is constructed for a
 * Map, it will always start at the prototype.
 *
 * The PrototypeIterator can either run to the null_value(), the first
 * non-hidden prototype, or a given object.
 */
class PrototypeIterator {
 public:
  enum WhereToStart { START_AT_RECEIVER, START_AT_PROTOTYPE };
 
  enum WhereToEnd { END_AT_NULL, END_AT_NON_HIDDEN };
 
  PrototypeIterator(Isolate* isolate, Handle<Object> receiver,
                    WhereToStart where_to_start = START_AT_PROTOTYPE)
      : did_jump_to_prototype_chain_(false),
        object_(NULL),
        handle_(receiver),
        isolate_(isolate) {
    CHECK(!handle_.is_null());
    if (where_to_start == START_AT_PROTOTYPE) {
      Advance();
    }
  }
  PrototypeIterator(Isolate* isolate, Object* receiver,
                    WhereToStart where_to_start = START_AT_PROTOTYPE)
      : did_jump_to_prototype_chain_(false),
        object_(receiver),
        isolate_(isolate) {
    if (where_to_start == START_AT_PROTOTYPE) {
      Advance();
    }
  }
  explicit PrototypeIterator(Map* receiver_map)
      : did_jump_to_prototype_chain_(true),
        object_(receiver_map->prototype()),
        isolate_(receiver_map->GetIsolate()) {}
  explicit PrototypeIterator(Handle<Map> receiver_map)
      : did_jump_to_prototype_chain_(true),
        object_(NULL),
        handle_(handle(receiver_map->prototype(), receiver_map->GetIsolate())),
        isolate_(receiver_map->GetIsolate()) {}
  ~PrototypeIterator() {}
 
  Object* GetCurrent() const {
    DCHECK(handle_.is_null());
    return object_;
  }
  static Handle<Object> GetCurrent(const PrototypeIterator& iterator) {
    DCHECK(!iterator.handle_.is_null());
    return iterator.handle_;
  }
  void Advance() {
    if (handle_.is_null() && object_->IsJSProxy()) {
      did_jump_to_prototype_chain_ = true;
      object_ = isolate_->heap()->null_value();
      return;
    } else if (!handle_.is_null() && handle_->IsJSProxy()) {
      did_jump_to_prototype_chain_ = true;
      handle_ = handle(isolate_->heap()->null_value(), isolate_);
      return;
    }
    AdvanceIgnoringProxies();
  }
  void AdvanceIgnoringProxies() {
    if (!did_jump_to_prototype_chain_) {
      did_jump_to_prototype_chain_ = true;
      if (handle_.is_null()) {
        object_ = object_->GetRootMap(isolate_)->prototype();
      } else {
        handle_ = handle(handle_->GetRootMap(isolate_)->prototype(), isolate_);
      }
    } else {
      if (handle_.is_null()) {
        object_ = HeapObject::cast(object_)->map()->prototype();
      } else {
        handle_ =
            handle(HeapObject::cast(*handle_)->map()->prototype(), isolate_);
      }
    }
  }
  bool IsAtEnd(WhereToEnd where_to_end = END_AT_NULL) const {
    if (handle_.is_null()) {
      return object_->IsNull() ||
             (did_jump_to_prototype_chain_ &&
              where_to_end == END_AT_NON_HIDDEN &&
              !HeapObject::cast(object_)->map()->is_hidden_prototype());
    } else {
      return handle_->IsNull() ||
             (did_jump_to_prototype_chain_ &&
              where_to_end == END_AT_NON_HIDDEN &&
              !Handle<HeapObject>::cast(handle_)->map()->is_hidden_prototype());
    }
  }
  bool IsAtEnd(Object* final_object) {
    DCHECK(handle_.is_null());
    return object_->IsNull() || object_ == final_object;
  }
  bool IsAtEnd(Handle<Object> final_object) {
    DCHECK(!handle_.is_null());
    return handle_->IsNull() || *handle_ == *final_object;
  }
 
 private:
  bool did_jump_to_prototype_chain_;
  Object* object_;
  Handle<Object> handle_;
  Isolate* isolate_;
 
  DISALLOW_COPY_AND_ASSIGN(PrototypeIterator);
};
 
 
}  // namespace internal
 
}  // namespace v8
 
#endif  // V8_PROTOTYPE_H_