v8/src/elements.h

// Copyright 2011 the V8 project authors. All rights reserved.
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#ifndef V8_ELEMENTS_H_
#define V8_ELEMENTS_H_

#include "objects.h"

namespace v8 {
namespace internal {

// Abstract base class for handles that can operate on objects with differing
// ElementsKinds.
class ElementsAccessor {
 public:
  ElementsAccessor() { }
  virtual ~ElementsAccessor() { }
  virtual MaybeObject* Get(FixedArrayBase* backing_store,
                           uint32_t key,
                           JSObject* holder,
                           Object* receiver) = 0;

  // Modifies the length data property as specified for JSArrays and resizes the
  // underlying backing store accordingly. The method honors the semantics of
  // changing array sizes as defined in EcmaScript 5.1 15.4.5.2, i.e. array that
  // have non-deletable elements can only be shrunk to the size of highest
  // element that is non-deletable.
  virtual MaybeObject* SetLength(JSObject* holder,
                                 Object* new_length) = 0;

  // Modifies both the length and capacity of a JSArray, resizing the underlying
  // backing store as necessary. This method does NOT honor the semantics of
  // EcmaScript 5.1 15.4.5.2, arrays can be shrunk beyond non-deletable
  // elements. This method should only be called for array expansion OR by
  // runtime JavaScript code that use InternalArrays and don't care about
  // EcmaScript 5.1 semantics.
  virtual MaybeObject* SetCapacityAndLength(JSArray* array,
                                            int capacity,
                                            int length) = 0;

  virtual MaybeObject* Delete(JSObject* holder,
                              uint32_t key,
                              JSReceiver::DeleteMode mode) = 0;

  virtual MaybeObject* AddElementsToFixedArray(FixedArrayBase* from,
                                               FixedArray* to,
                                               JSObject* holder,
                                               Object* receiver) = 0;

  // Returns a shared ElementsAccessor for the specified ElementsKind.
  static ElementsAccessor* ForKind(ElementsKind elements_kind) {
    ASSERT(elements_kind < kElementsKindCount);
    return elements_accessors_[elements_kind];
  }

  static ElementsAccessor* ForArray(FixedArrayBase* array);

  static void InitializeOncePerProcess();

 protected:
  friend class NonStrictArgumentsElementsAccessor;

  virtual uint32_t GetCapacity(FixedArrayBase* backing_store) = 0;

  virtual bool HasElementAtIndex(FixedArrayBase* backing_store,
                                 uint32_t index,
                                 JSObject* holder,
                                 Object* receiver) = 0;

  // Element handlers distinguish between indexes and keys when the manipulate
  // elements.  Indexes refer to elements in terms of their location in the
  // underlying storage's backing store representation, and are between 0
  // GetCapacity.  Keys refer to elements in terms of the value that would be
  // specific in JavaScript to access the element. In most implementations, keys
  // are equivalent to indexes, and GetKeyForIndex returns the same value it is
  // passed. In the NumberDictionary ElementsAccessor, GetKeyForIndex maps the
  // index to a key using the KeyAt method on the NumberDictionary.
  virtual uint32_t GetKeyForIndex(FixedArrayBase* backing_store,
                                  uint32_t index) = 0;

 private:
  static ElementsAccessor** elements_accessors_;

  DISALLOW_COPY_AND_ASSIGN(ElementsAccessor);
};

} }  // namespace v8::internal

#endif  // V8_ELEMENTS_H_