Add @@iterator support for strings

src/string-iterator.js

Index: src/string-iterator.js
diff --git a/src/string-iterator.js b/src/string-iterator.js
new file mode 100644
index 0000000000000000000000000000000000000000..210f36e5d897af441098edf6a1942a16228c87f2
--- /dev/null
+++ b/src/string-iterator.js
@@ -0,0 +1,106 @@
+// 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");
+
+
+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;

[arv (Not doing code reviews), 2014/06/17 15:33:19]

wrong indentation

[wingo, 2014/06/18 08:34:07]

Done.

+}
+
+
+// 21.1.5.2.1 %StringIteratorPrototype%.next( )
+function StringIteratorNext() {
+  var iterator = ToObject(this);
+
+  if (!HAS_PRIVATE(iterator, stringIteratorIteratedStringSymbol)) {
+    throw MakeTypeError('incompatible_method_receiver',
+                        ['String Iterator.prototype.next']);
+  }
+
+  var s = GET_PRIVATE(iterator, stringIteratorIteratedStringSymbol);
+  if (IS_UNDEFINED(s)) {
+    return CreateIteratorResultObject(UNDEFINED, true);
+  }
+
+  var position = GET_PRIVATE(iterator, stringIteratorNextIndexSymbol);
+  var length = TO_UINT32(s.length);
+
+  if (position >= length) {
+    SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol, UNDEFINED);
+    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) {
+      resultString += %_StringCharFromCode(second);
+      position++;
+    }
+  }
+
+  SET_PRIVATE(iterator, stringIteratorNextIndexSymbol, position);
+
+  return CreateIteratorResultObject(resultString, false);
+}
+
+
+function SetUpStringIterator() {
+  %CheckIsBootstrapping();
+
+  %FunctionSetPrototype(StringIterator, new $Object());
+  %FunctionSetInstanceClassName(StringIterator, 'String Iterator');
+
+  InstallFunctions(StringIterator.prototype, DONT_ENUM, $Array(
+    'next', StringIteratorNext
+  ));
+  %FunctionSetName(StringIteratorIterator, '[Symbol.iterator]');
+  %SetProperty(StringIterator.prototype, symbolIterator, StringIteratorIterator,
+      DONT_ENUM | DONT_DELETE | READ_ONLY);
+}
+SetUpStringIterator();
+
+
+// 21.1.3.27 String.prototype [ @@iterator ]( )
+function StringPrototypeIterator() {
+  return CreateStringIterator(this);
+}
+
+
+function ExtendStringPrototypeWithIterator() {
+  %CheckIsBootstrapping();
+
+  %FunctionSetName(StringPrototypeIterator, '[Symbol.iterator]');
+  %SetProperty($String.prototype, symbolIterator, StringPrototypeIterator,
+      DONT_ENUM | DONT_DELETE | READ_ONLY);

[arv (Not doing code reviews), 2014/06/17 15:33:19]

Why read only and dont delete?

[wingo, 2014/06/18 08:34:06]

Copy-paste cargo culting.  Fixed.

+}
+ExtendStringPrototypeWithIterator();