a === b -> identical(a, b)

runtime/lib/immutable_map.dart

 // Copyright (c) 2012, 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.
 // Immutable map class for compiler generated map literals.
 
 class ImmutableMap<K, V> implements Map<K, V> {
   final _ImmutableArray kvPairs_;
 
   const ImmutableMap._create(_ImmutableArray keyValuePairs)
       : kvPairs_ = keyValuePairs;
 
 
   V operator [](K key) {
     // TODO(hausner): Since the keys are sorted, we could do a binary
     // search. But is it worth it?
     for (int i = 0; i < kvPairs_.length - 1; i += 2) {
       if (key == kvPairs_[i]) {
         return kvPairs_[i+1];
       }
     }
     return null;
   }
 
   bool get isEmpty {
-    return kvPairs_.length === 0;
+    return kvPairs_.length == 0;
   }
 
   int get length {
     return kvPairs_.length ~/ 2;
   }
 
   void forEach(void f(K key, V value)) {
     for (int i = 0; i < kvPairs_.length; i += 2) {
       f(kvPairs_[i], kvPairs_[i+1]);
     }
@@ skipping 49 matching lines @@
 
   V remove(K key) {
     throw new UnsupportedError("Cannot remove from unmodifiable Map");
   }
 
   String toString() {
     return Maps.mapToString(this);
   }
 }