Add List.asMap().

tests/corelib/list_as_map_test.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+void testListMapCorrespondence(List list, Map map) {
+  Expect.equals(list.length, map.length);
+  for (int i = 0; i < list.length; i++) {
+    Expect.equals(list[i], map[i]);
+  }
+  Expect.isNull(map[list.length]);
+  Expect.isNull(map[-1]);
+
+  Iterable keys = map.keys;
+  Iterable values = map.values;
+  Expect.isFalse(keys is List);
+  Expect.isFalse(values is List);
+  Expect.equals(list.length, keys.length);
+  Expect.equals(list.length, values.length);
+  for (int i = 0; i < list.length; i++) {
+    Expect.equals(i, keys.elementAt(i));
+    Expect.equals(list[i], values.elementAt(i));
+  }
+
+  int forEachCount = 0;
+  map.forEach((key, value) {
+    Expect.equals(forEachCount, key);
+    Expect.equals(list[key], value);
+    forEachCount++;
+  });
+
+  for (int i = 0; i < list.length; i++) {
+    Expect.isTrue(map.containsKey(i));
+    Expect.isTrue(map.containsValue(list[i]));
+  }
+  Expect.isFalse(map.containsKey(-1));
+  Expect.isFalse(map.containsKey(list.length));
+
+  Expect.equals(list.length, forEachCount);
+
+  Expect.equals(list.isEmpty, map.isEmpty);
+}
+
+void testAsMap(List list, bool canBeModified, bool canGrow) {
+  Map<int, dynamic> map = list.asMap();
+
+  testListMapCorrespondence(list, map);
+
+  Expect.throws(() => map[0] = 499,
+                (e) => e is UnsupportedError);
+  Expect.throws(() => map.putIfAbsent(0, () => 499),
+                (e) => e is UnsupportedError);
+  Expect.throws(() => map.clear(),
+                (e) => e is UnsupportedError);
+
+  if (!canBeModified) return;

[Lasse Reichstein Nielsen, 2013/03/04 08:28:37]

Instead of passing anonymous booleans, you can have three functions:
testConstAsMap, testFixedAsMap, testAsMap, with that last two  calling the prior
one as well as adding its own tests.

[floitsch, 2013/03/04 16:50:20]

Done.

+
+  if (!list.isEmpty) {
+    list[0] = 499;
+    // Check again to make sure the map is backed by the list.
+    testListMapCorrespondence(list, map);
+  }
+
+  if (!canGrow) return;
+
+  Iterable keys = map.keys;
+  Iterable values = map.values;
+
+  list.add(42);
+  // Check again to make sure the map is backed by the list and that the
+  // length is not cached.
+  testListMapCorrespondence(list, map);
+  // Also check that the keys and values iterable from the map are backed by
+  // the list.
+  Expect.equals(list.length, keys.length);
+  Expect.equals(values.length, values.length);
+}
+
+main() {
+  testAsMap(const [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], false, false);
+  testAsMap([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], true, true);
+  List list = new List(10);
+  for (int i = 0; i < 10; i++) list[i] = i + 1;
+  testAsMap(list, true, false);
+
+  testAsMap(const [], false, false);
+  testAsMap([], true, true);
+  testAsMap(new List(0), true, false);
+}