Arguments object has @@iterator

test/mjsunit/harmony/arguments-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.
+
+// Flags: --harmony-iteration
+
+
+// Note in general that "arguments.foo" and "var o = arguments; o.foo"
+// are treated differently by full-codegen, and so both cases need to be
+// tested.
+
+function TestDirectArgumentsIteratorProperty() {
+  assertTrue(arguments.hasOwnProperty(Symbol.iterator));
+  assertFalse(arguments.propertyIsEnumerable(Symbol.iterator));
+  assertEquals(arguments[Symbol.iterator], [].values);
+}
+TestDirectArgumentsIteratorProperty();
+
+
+function TestIndirectArgumentsIteratorProperty() {
+  var o = arguments;
+  assertTrue(o.hasOwnProperty(Symbol.iterator));
+  assertFalse(o.propertyIsEnumerable(Symbol.iterator));
+  assertEquals(o[Symbol.iterator], [].values);
+}
+TestIndirectArgumentsIteratorProperty();
+
+
+function assertIteratorResult(value, done, result) {
+  assertEquals({value: value, done: done}, result);
+}
+
+
+function TestDirectValues1(a, b, c) {
+  var iterator = arguments[Symbol.iterator]();
+  assertIteratorResult(a, false, iterator.next());
+  assertIteratorResult(b, false, iterator.next());
+  assertIteratorResult(c, false, iterator.next());
+  assertIteratorResult(void 0, true, iterator.next());

[rossberg, 2014/06/26 15:51:53]

Nit: no reason to use void 0 instead of undefined in tests.

+}
+TestDirectValues1(1, 2, 3);
+
+
+function TestIndirectValues1(a, b, c) {
+  var args = arguments;
+  var iterator = args[Symbol.iterator]();
+  assertIteratorResult(a, false, iterator.next());
+  assertIteratorResult(b, false, iterator.next());
+  assertIteratorResult(c, false, iterator.next());
+  assertIteratorResult(void 0, true, iterator.next());
+}
+TestIndirectValues1(1, 2, 3);
+
+
+function TestDirectValues2(a, b, c) {
+  var iterator = arguments[Symbol.iterator]();
+  assertIteratorResult(a, false, iterator.next());
+  assertIteratorResult(b, false, iterator.next());
+  assertIteratorResult(c, false, iterator.next());
+  assertIteratorResult(void 0, true, iterator.next());
+
+  arguments[3] = 4;
+  arguments.length = 4;
+  assertIteratorResult(void 0, true, iterator.next());
+}
+TestDirectValues2(1, 2, 3);
+
+
+function TestIndirectValues2(a, b, c) {
+  var args = arguments;
+  var iterator = args[Symbol.iterator]();
+  assertIteratorResult(a, false, iterator.next());
+  assertIteratorResult(b, false, iterator.next());
+  assertIteratorResult(c, false, iterator.next());
+  assertIteratorResult(void 0, true, iterator.next());
+
+  arguments[3] = 4;
+  arguments.length = 4;
+  assertIteratorResult(void 0, true, iterator.next());
+}
+TestIndirectValues2(1, 2, 3);
+
+
+function TestDirectValues3(a, b, c) {
+  var iterator = arguments[Symbol.iterator]();
+  assertIteratorResult(a, false, iterator.next());
+  assertIteratorResult(b, false, iterator.next());
+
+  arguments.length = 2;
+  assertIteratorResult(void 0, true, iterator.next());
+}
+TestDirectValues3(1, 2, 3);
+
+
+function TestIndirectValues3(a, b, c) {
+  var args = arguments;
+  var iterator = args[Symbol.iterator]();
+  assertIteratorResult(a, false, iterator.next());
+  assertIteratorResult(b, false, iterator.next());
+
+  arguments.length = 2;
+  assertIteratorResult(void 0, true, iterator.next());
+}
+TestIndirectValues3(1, 2, 3);
+
+
+function TestDirectValues4(a, b, c) {
+  var iterator = arguments[Symbol.iterator]();
+  assertIteratorResult(a, false, iterator.next());
+  assertIteratorResult(b, false, iterator.next());
+  assertIteratorResult(c, false, iterator.next());
+
+  arguments.length = 4;
+  assertIteratorResult(void 0, false, iterator.next());
+  assertIteratorResult(void 0, true, iterator.next());
+}
+TestDirectValues4(1, 2, 3);
+
+
+function TestIndirectValues4(a, b, c) {

[rossberg, 2014/06/26 15:51:52]

It would be good to also test that

- changing an arguments slot is reflected in the iterator
- changing a sloppy arguments slot through an aliased parameter variable is
reflected in the iterator
- changing a parameter variable does not effect strict arguments iteration

+  var args = arguments;
+  var iterator = args[Symbol.iterator]();
+  assertIteratorResult(a, false, iterator.next());
+  assertIteratorResult(b, false, iterator.next());
+  assertIteratorResult(c, false, iterator.next());
+
+  arguments.length = 4;
+  assertIteratorResult(void 0, false, iterator.next());
+  assertIteratorResult(void 0, true, iterator.next());
+}
+TestIndirectValues4(1, 2, 3);
+
+
+function TestForOf() {
+  var i = 0;
+  for (var value of arguments) {
+    assertEquals(arguments[i++], value);
+  }
+
+  assertEquals(arguments.length, i);
+}
+TestForOf(1, 2, 3, 4, 5);
+
+
+function TestAssignmentToIterator() {
+  var i = 0;
+  arguments[Symbol.iterator] = [].entries;
+  for (var entry of arguments) {
+    assertEquals([i, arguments[i]], entry);
+    i++;
+  }
+
+  assertEquals(arguments.length, i);
+}
+TestAssignmentToIterator(1, 2, 3, 4, 5);