Define equality for boolean selectors.

lib/src/union_selector.dart

 // Copyright (c) 2016, 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.
 
 import '../boolean_selector.dart';
 import 'intersection_selector.dart';
 
 /// A selector that matches inputs that either of its sub-selectors match.
 class UnionSelector implements BooleanSelector {
   final BooleanSelector _selector1;
@@ skipping 12 matching lines @@
 
   BooleanSelector union(BooleanSelector other) =>
       new UnionSelector(this, other);
 
   void validate(bool isDefined(String variable)) {
     _selector1.validate(isDefined);
     _selector2.validate(isDefined);
   }
 
   String toString() => "($_selector1) && ($_selector2)";
+
+  bool operator==(other) =>
+      other is UnionSelector &&
+      _selector1 == other._selector1 &&
+      _selector2 == other._selector2;
+
+  int get hashCode => _selector1.hashCode ^ _selector2.hashCode;
 }