Add a CanonicalizedMap class to pkg/collection.

pkg/collection/lib/src/utils.dart

+// Copyright (c) 2014, 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.
+
+library dart.pkg.collection.utils;
+
+/// A pair of values.
+class Pair<E, F> {
+  E first;
+  F last;
+
+  Pair(this.first, this.last);
+
+  String toString() => '($first, $last)';
+
+  bool operator==(other) {
+    if (other is! Pair) return false;
+    return other.first == first && other.last == last;
+  }
+
+  int get hashCode => first.hashCode ^ last.hashCode;

[Lasse Reichstein Nielsen, 2014/07/01 09:18:15]

I'd prefer some less symmetric operation, like
  => (first.hashCode * 37 + last.hashCode) & 0x3fffffff;

The plain xor gives zero if first and last are the same value, which is too
likely a case in general.
(We don't use the hashCode for anything, right? Would it be safe to remove
toString, == and hashCode until we actually need it? I'm thinking it's methods
that dart2js would not be able to tree-shake in general, so the extra code could
be (slightly) harmful).

[nweiz, 2014/07/01 21:21:44]

Removed these.

+}