Allow TypedArrays to be initialized with iterables

src/typedarray.js

 // Copyright 2013 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.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 112 matching lines @@
   }
   if (!initialized) {
     for (var i = 0; i < l; i++) {
       // It is crucial that we let any execptions from arrayLike[i]
       // propagate outside the function.
       obj[i] = arrayLike[i];
     }
   }
 }
 
+function NAMEConstructByIterable(obj, iterable) {
+  var list = new InternalArray();
+  for (var element of iterable) {
+    list.push(element);
+  }
+  return NAMEConstructByArrayLike(obj, list);
+}
+
 function NAMEConstructor(arg1, arg2, arg3) {
   if (%_IsConstructCall()) {
     if (IS_ARRAYBUFFER(arg1) || IS_SHAREDARRAYBUFFER(arg1)) {
       NAMEConstructByArrayBuffer(this, arg1, arg2, arg3);
     } else if (IS_NUMBER(arg1) || IS_STRING(arg1) ||
                IS_BOOLEAN(arg1) || IS_UNDEFINED(arg1)) {
       NAMEConstructByLength(this, arg1);
     } else {
-      NAMEConstructByArrayLike(this, arg1);
+      var iteratorFn = arg1[Symbol.iterator];
+      if (IS_UNDEFINED(iteratorFn) || iteratorFn === $arrayValues) {
+        NAMEConstructByArrayLike(this, arg1);
+      } else {
+        // TODO(littledan): The code here is lazy and looks up @@iterator
+        // twice. Currently, that's fine, but it'll be observable with proxies.

[adamk, 2015/06/12 00:57:08]

Proxies aren't required, a getter for @@iterator is sufficient to detect this.
Let's fix it now.

[caitp (gmail), 2015/06/12 01:11:33]

I think the only way to really fix that currently is to write the loop by hand
:( As is done in ArrayFrom --- Is there a better way?

[Dan Ehrenberg, 2015/06/12 02:42:22]

Well, you can use for-of on most of the builtin iterators (generators, array
iterators, etc), as the iterator defines [Symbol.iterator]() to return this, but
that's not really part of the standard iteration protocol, so I won't depend on
it here. The loop wasn't so bad.

+        NAMEConstructByIterable(this, arg1);
+      }
     }
   } else {
     throw MakeTypeError(kConstructorNotFunction, "NAME")
   }
 }
 
 function NAME_GetBuffer() {
   if (!(%_ClassOf(this) === 'NAME')) {
     throw MakeTypeError(kIncompatibleMethodReceiver, "NAME.buffer", this);
   }
@@ skipping 321 matching lines @@
   "setUint32", DataViewSetUint32JS,
 
   "getFloat32", DataViewGetFloat32JS,
   "setFloat32", DataViewSetFloat32JS,
 
   "getFloat64", DataViewGetFloat64JS,
   "setFloat64", DataViewSetFloat64JS
 ]);
 
 })