Navigation extension point.

pkg/analysis_server/lib/src/collections.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 collections;
 
 /**
  * Returns the concatentation of the input iterables.
  *
  * The returned iterable is a lazily-evaluated view on the input iterables.
@@ skipping 10 matching lines @@
  */
 List nullIfEmpty(List list) {
   if (list == null) {
     return null;
   }
   if (list.isEmpty) {
     return null;
   }
   return list;
 }
+
+/// A pair of values.
+class Pair<E, F> {
+  final E first;
+  final F last;
+
+  Pair(this.first, this.last);
+
+  int get hashCode => first.hashCode ^ last.hashCode;
+
+  bool operator ==(other) {
+    if (other is! Pair) return false;
+    return other.first == first && other.last == last;
+  }
+
+  String toString() => '($first, $last)';
+}