Allow TypedArrays to be initialized with iterables

src/typedarray.js

Index: src/typedarray.js
diff --git a/src/typedarray.js b/src/typedarray.js
index 65659147ee7777cf1e8bc69196d4fc09a4beee89..2f9d052fce771131e66f96853c03b7f9307cc1b2 100644
--- a/src/typedarray.js
+++ b/src/typedarray.js
@@ -130,6 +130,14 @@ function NAMEConstructByArrayLike(obj, arrayLike) {
   }
 }
 
+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)) {
@@ -138,7 +146,14 @@ function NAMEConstructor(arg1, arg2, arg3) {
                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")