Encapsulate element handling into a class keyed on ElementsKind

src/elements.h

+// Copyright 2011 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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_ELEMENTS_H_
+#define V8_ELEMENTS_H_
+
+#include "objects.h"
+
+namespace v8 {
+namespace internal {
+
+// Abstract base class for handles that can operate on object with differing

[Rico, 2011/08/01 07:33:27]

on object -> an object or objects

[danno, 2011/08/02 13:37:46]

Done.

+// ElementsKinds.
+class ElementsHandler {

[Lasse Reichstein, 2011/08/01 09:35:54]

What does "Handler" mean. Seems too generic to be meaningful.

[danno, 2011/08/02 13:37:46]

My plan is to have this class house all of the element-related operations, so I
changed the name to Accessor. 

On 2011/08/01 09:35:54, Lasse Reichstein wrote:

+ public:
+  ElementsHandler() { }
+  virtual ~ElementsHandler() { }
+  virtual bool GetWithReceiver(JSObject* obj,
+                               Object* receiver,
+                               uint32_t index,
+                               MaybeObject** result) = 0;
+
+  // Returns a shared ElementsHandler for the specified ElementsKind.
+  inline static ElementsHandler* ForKind(JSObject::ElementsKind elements_kind) {

[Kevin Millikin (Chromium), 2011/08/01 10:18:23]

No need for 'inline'.  Maybe the function name/signature should be something
like SingletonFor(JSObject::ElementsKind).

[Lasse Reichstein, 2011/08/01 10:47:13]

We should probably not call it anything with "Singleton", since that's a less
general (anti-)pattern (and we don't implement each class as a Singleton class -
which is a good thing!).
This is more like an object-based enum (q.v. the Java enums, where,
incidentally, "enum Foo" is implemented internally as "class Foo extends
Enum<Foo>" :)

[danno, 2011/08/02 13:37:46]

Done.

[danno, 2011/08/02 13:37:46]

singleton is not quite right, and I actually like the current naming. in the
code you get something like this:

ElementsAccessor::ForKind(...)

I am not sure that adding Singleton, or ObjectEnum or something of the like will
improve readability. But I'm happy to change it if you feel strongly.

On 2011/08/01 10:47:13, Lasse Reichstein wrote:

+    ASSERT(elements_kind < JSObject::kElementsKindCount);
+    return elements_handler_table_[elements_kind];
+  }
+
+ private:
+  static ElementsHandler* elements_handler_table_[];
+
+  DISALLOW_COPY_AND_ASSIGN(ElementsHandler);
+};
+
+} }  // namespace v8::internal
+
+#endif  // V8_ELEMENTS_H_