src/elements.h

// Copyright 2012 the V8 project authors. All rights reserved.
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#ifndef V8_ELEMENTS_H_
#define V8_ELEMENTS_H_

#include "objects.h"
#include "heap.h"
#include "isolate.h"

namespace v8 {
namespace internal {

// Abstract base class for handles that can operate on objects with differing
// ElementsKinds.
class ElementsAccessor {
 public:
  explicit ElementsAccessor(const char* name) : name_(name) { }
  virtual ~ElementsAccessor() { }

  virtual ElementsKind kind() const = 0;
  const char* name() const { return name_; }

  // Returns true if a holder contains an element with the specified key
  // without iterating up the prototype chain.  The caller can optionally pass
  // in the backing store to use for the check, which must be compatible with
  // the ElementsKind of the ElementsAccessor. If backing_store is NULL, the
  // holder->elements() is used as the backing store.
  virtual bool HasElement(Object* receiver,
                          JSObject* holder,
                          uint32_t key,
                          FixedArrayBase* backing_store = NULL) = 0;

  // Returns the element with the specified key or undefined if there is no such
  // element. This method doesn't iterate up the prototype chain.  The caller
  // can optionally pass in the backing store to use for the check, which must
  // be compatible with the ElementsKind of the ElementsAccessor. If
  // backing_store is NULL, the holder->elements() is used as the backing store.
  virtual MaybeObject* Get(Object* receiver,
                           JSObject* holder,
                           uint32_t key,
                           FixedArrayBase* backing_store = NULL) = 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(JSArray* 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;

  // Deletes an element in an object, returning a new elements backing store.
  virtual MaybeObject* Delete(JSObject* holder,
                              uint32_t key,
                              JSReceiver::DeleteMode mode) = 0;

  // If kCopyToEnd is specified as the copy_size to CopyElements, it copies all
  // of elements from source after source_start to the destination array.
  static const int kCopyToEnd = -1;
  // If kCopyToEndAndInitializeToHole is specified as the copy_size to
  // CopyElements, it copies all of elements from source after source_start to
  // destination array, padding any remaining uninitialized elements in the
  // destination array with the hole.
  static const int kCopyToEndAndInitializeToHole = -2;

  // Copy elements from one backing store to another. Typically, callers specify
  // the source JSObject or JSArray in source_holder. If the holder's backing
  // store is available, it can be passed in source and source_holder is
  // ignored.
  virtual MaybeObject* CopyElements(JSObject* source_holder,
                                    uint32_t source_start,
                                    FixedArrayBase* destination,
                                    ElementsKind destination_kind,
                                    uint32_t destination_start,
                                    int copy_size,
                                    FixedArrayBase* source = NULL) = 0;

  MaybeObject* CopyElements(JSObject* from_holder,
                            FixedArrayBase* to,
                            ElementsKind to_kind,
                            FixedArrayBase* from = NULL) {
    return CopyElements(from_holder, 0, to, to_kind, 0,
                        kCopyToEndAndInitializeToHole, from);
  }

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

  // Element handlers distinguish between indexes and keys when they manipulate
  // elements.  Indexes refer to elements in terms of their location in the
  // underlying storage's backing store representation, and are between 0 and
  // GetCapacity.  Keys refer to elements in terms of the value that would be
  // specified 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_;
  const char* name_;

  DISALLOW_COPY_AND_ASSIGN(ElementsAccessor);
};


void CopyObjectToObjectElements(FixedArray* from_obj,
                                ElementsKind from_kind,
                                uint32_t from_start,
                                FixedArray* to_obj,
                                ElementsKind to_kind,
                                uint32_t to_start,
                                int copy_size);


} }  // namespace v8::internal

#endif  // V8_ELEMENTS_H_