Make all global private symbols own symbols.

src/string-iterator.js

 // 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.
 
 'use strict';
 
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $String = global.String;
 
 
 var stringIteratorIteratedStringSymbol =
-    GLOBAL_PRIVATE("StringIterator#iteratedString");
-var stringIteratorNextIndexSymbol = GLOBAL_PRIVATE("StringIterator#next");
+    GLOBAL_PRIVATE_OWN("StringIterator#iteratedString");
+var stringIteratorNextIndexSymbol = GLOBAL_PRIVATE_OWN("StringIterator#next");
+
+var stringEndOfIterationMarker = new $Object();
 
 
 function StringIterator() {}
 
 
 // 21.1.5.1 CreateStringIterator Abstract Operation
 function CreateStringIterator(string) {
   var s = TO_STRING_INLINE(string);
   var iterator = new StringIterator;
   SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol, s);
   SET_PRIVATE(iterator, stringIteratorNextIndexSymbol, 0);
   return iterator;
 }
 
 
 // 21.1.5.2.2 %StringIteratorPrototype%[@@iterator]
 function StringIteratorIterator() {
   return this;
 }
 
 
 // 21.1.5.2.1 %StringIteratorPrototype%.next( )
 function StringIteratorNext() {
   var iterator = ToObject(this);
 
-  if (!HAS_PRIVATE(iterator, stringIteratorIteratedStringSymbol)) {
+  if (!HAS_DEFINED_PRIVATE(iterator, stringIteratorIteratedStringSymbol)) {
     throw MakeTypeError('incompatible_method_receiver',
                         ['String Iterator.prototype.next']);
   }
 
   var s = GET_PRIVATE(iterator, stringIteratorIteratedStringSymbol);
-  if (IS_UNDEFINED(s)) {
+  if (s === stringEndOfIterationMarker) {

[wingo, 2014/08/20 15:32:53]

Wouldn't stringEndOfIterationMarker be per-realm?  I always get this stuff
wrong.

[arv (Not doing code reviews), 2014/08/20 15:39:26]

You are right. This is not going to work.

I don't see why we cannot continue to use undefined here?

[Dmitry Lomov (no reviews), 2014/08/20 17:01:37]

Thanks, good catch, I haven't thought of that.
It's because I have changed the HAS_PRIVATE above to essentially
  iterator[stringIteratorIteratedStringSymbol] === undefined
There are two things I could do:
1) Either keep using %HasOwnProperty above (runtime call)
2) Or use a different symbol for branding (string iterators bigger by 1 field)

Opinions? 

[arv (Not doing code reviews), 2014/08/20 18:07:07]

In this case and for the ArrayIterator we can check
stringIteratorNextIndexSymbol instead. We set this to 0 in CreateStringIterator
so the "brand" check can be changed to !IS_UNDEFINED(GET_PRIVATE(iterator,
stringIteratorNextIndexSymbol)), which I goes is what HAS_DEFINED_PRIVATE does.

     return CreateIteratorResultObject(UNDEFINED, true);
   }
 
   var position = GET_PRIVATE(iterator, stringIteratorNextIndexSymbol);
   var length = TO_UINT32(s.length);
 
   if (position >= length) {
-    SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol, UNDEFINED);
+    SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol,
+                stringEndOfIterationMarker);
     return CreateIteratorResultObject(UNDEFINED, true);
   }
 
   var first = %_StringCharCodeAt(s, position);
   var resultString = %_StringCharFromCode(first);
   position++;
 
   if (first >= 0xD800 && first <= 0xDBFF && position < length) {
     var second = %_StringCharCodeAt(s, position);
     if (second >= 0xDC00 && second <= 0xDFFF) {
@@ skipping 31 matching lines @@
 
 
 function ExtendStringPrototypeWithIterator() {
   %CheckIsBootstrapping();
 
   %FunctionSetName(StringPrototypeIterator, '[Symbol.iterator]');
   %AddNamedProperty($String.prototype, symbolIterator,
                     StringPrototypeIterator, DONT_ENUM);
 }
 ExtendStringPrototypeWithIterator();