Use an ES6 map for a linked identity hash map.

sdk/lib/_internal/compiler/js_lib/collection_patch.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.
 
 // Patch file for dart:collection classes.
 import 'dart:_foreign_helper' show JS;
 import 'dart:_js_helper' show
     fillLiteralMap, InternalMap, NoInline, NoSideEffects, NoThrows, patch,
     JsLinkedHashMap, LinkedHashMapCell, LinkedHashMapKeyIterable,
     LinkedHashMapKeyIterator;
 
+const _USE_ES6_MAPS = const bool.fromEnvironment("dart2js.use.es6.maps");
+
 @patch
 class HashMap<K, V> {
   @patch
   factory HashMap({ bool equals(K key1, K key2),
                     int hashCode(K key),
                     bool isValidKey(potentialKey) }) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
           return new _HashMap<K, V>();
@@ skipping 471 matching lines @@
                           bool isValidKey(potentialKey) }) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
           return new JsLinkedHashMap<K, V>.es6();
         }
         hashCode = _defaultHashCode;
       } else {
         if (identical(identityHashCode, hashCode) &&
             identical(identical, equals)) {
-          return new _LinkedIdentityHashMap<K, V>();
+          return new _LinkedIdentityHashMap<K, V>.es6();
         }
         if (equals == null) {
           equals = _defaultEquals;
         }
       }
     } else {
       if (hashCode == null) {
         hashCode = _defaultHashCode;
       }
       if (equals == null) {
         equals = _defaultEquals;
       }
     }
     return new _LinkedCustomHashMap<K, V>(equals, hashCode, isValidKey);
   }
 
   @patch
-  factory LinkedHashMap.identity() = _LinkedIdentityHashMap<K, V>;
+  factory LinkedHashMap.identity() = _LinkedIdentityHashMap<K, V>.es6;
 
   // Private factory constructor called by generated code for map literals.
   @NoInline()
   factory LinkedHashMap._literal(List keyValuePairs) {
     return fillLiteralMap(keyValuePairs, new JsLinkedHashMap<K, V>.es6());
   }
 
   // Private factory constructor called by generated code for map literals.
   @NoThrows() @NoInline() @NoSideEffects()
   factory LinkedHashMap._empty() {
     return new JsLinkedHashMap<K, V>.es6();
   }
 
   // Private factory static function called by generated code for map literals.
   // This version is for map literals without type parameters.
   @NoInline()
   static _makeEmpty() => new JsLinkedHashMap();
 
   // Private factory static function called by generated code for map literals.
   // This version is for map literals without type parameters.
   @NoInline()
   static _makeLiteral(keyValuePairs) =>
       fillLiteralMap(keyValuePairs, new JsLinkedHashMap());
 }
 
-// TODO(floitsch): use ES6 Maps when available.
 class _LinkedIdentityHashMap<K, V> extends JsLinkedHashMap<K, V> {
+  static bool get _supportsEs6Maps {
+    return JS('returns:bool;depends:none;effects:none;throws:never;gvn:true',
+    'typeof Map != "undefined"');

[floitsch, 2015/06/18 09:48:19]

indent.

[Harry Terkelsen, 2015/06/18 16:12:36]

Done.

+  }
+
+  factory _LinkedIdentityHashMap.es6() {
+    return (_USE_ES6_MAPS && _LinkedIdentityHashMap._supportsEs6Maps)
+      ? new _LinkedIdentityHashMap<K, V>()

[floitsch, 2015/06/18 09:48:19]

indent by 2 more.

[Harry Terkelsen, 2015/06/18 16:12:36]

Done.

+      : new _Es6LinkedIdentityHashMap<K, V>();
+  }
+
+  _LinkedIdentityHashMap();
+
   int internalComputeHashCode(var key) {
     // We force the hash codes to be unsigned 30-bit integers to avoid
     // issues with problematic keys like '__proto__'. Another option
     // would be to throw an exception if the hash code isn't a number.
     return JS('int', '# & 0x3ffffff', identityHashCode(key));
   }
 
   int internalFindBucketIndex(var bucket, var key) {
     if (bucket == null) return -1;
     int length = JS('int', '#.length', bucket);
     for (int i = 0; i < length; i++) {
       LinkedHashMapCell cell = JS('var', '#[#]', bucket, i);
       if (identical(cell.hashMapCellKey, key)) return i;
     }
     return -1;
   }
 }
 
+class _Es6LinkedIdentityHashMap<K, V>
+    implements LinkedHashMap<K, V>, InternalMap {
+  final _map;
+  int _modifications = 0;
+
+  _Es6LinkedIdentityHashMap() : _map = JS('var', 'new Map()');
+
+  int get length => JS('int', '#.size', _map);
+  bool get isEmpty => length == 0;
+  bool get isNotEmpty => !isEmpty;
+
+  Iterable<K> get keys => new _Es6MapIterable<K>(this, true);
+
+  Iterable<V> get values =>
+      new _Es6MapIterable<V>(this, false);
+
+  bool containsKey(Object key) {
+    return JS('bool', '#.has(#)', _map, key);
+  }
+
+  bool containsValue(Object value) {
+    return values.any((each) => each == value);
+  }
+
+  void addAll(Map<K, V> other) {
+    other.forEach((K key, V value) {
+      this[key] = value;
+      _modified();
+    });
+  }
+
+  V operator[](Object key) {
+    var value = JS('var', '#.get(#)', _map, key);
+    bool isUndefined = JS('bool', '# === "undefined"', value);
+    return isUndefined ? null : value;

[floitsch, 2015/06/18 09:48:19]

why not just return the value?
undefined and null behave the same way in dart2js.

[Harry Terkelsen, 2015/06/18 16:12:36]

good to know

+  }
+
+  void operator[]=(K key, V value) {
+    JS('var', '#.set(#, #)', _map, key, value);
+    _modified();
+  }
+
+  V putIfAbsent(K key, V ifAbsent()) {
+    if (containsKey(key)) return this[key];
+    V value = ifAbsent();
+    this[key] = value;
+    _modified();
+    return value;
+  }
+
+  V remove(Object key) {
+    V value = this[key];
+    JS('bool', '#.delete(#)', _map, key);
+    _modified();
+    return value;
+  }
+
+  void clear() {
+    JS('void', '#.clear()', _map);
+    _modified();
+  }
+
+  void forEach(void action(K key, V value)) {
+    var jsEntries = JS('var', '#.entries()', _map);
+    int modifications = _modifications;
+    while (true) {
+      var next = JS('var', '#.next()', jsEntries);
+      bool done = JS('bool', '#.done', next);
+      if (done) break;
+      var entry = JS('var', '#.value', next);
+      var key = JS('var', '#[0]', entry);
+      var value = JS('var', '#[1]', entry);
+      action(key, value);
+      if (modifications != _modifications) {
+        throw new ConcurrentModificationError(this);
+      }
+    }
+  }
+
+  void _modified() {
+    // Value cycles after 2^30 modifications. If you keep hold of an
+    // iterator for that long, you might miss a modification
+    // detection, and iteration can go sour. Don't do that.
+    _modifications = (_modifications + 1) & 0x3ffffff;
+  }
+
+  String toString() => Maps.mapToString(this);
+}
+
+class _Es6MapIterable<E> extends Iterable<E>
+                         implements EfficientLength {
+  final _map;
+  final bool _isKeys;
+
+  _Es6MapIterable(this._map, this._isKeys);
+
+  int get length => _map.length;
+  bool get isEmpty => _map.isEmpty;
+
+  Iterator<E> get iterator =>
+      new _Es6MapIterator<E>(_map, _map._modifications, _isKeys);
+
+  bool contains(Object element) => _map.containsKey(element);
+
+  void forEach(void f(E element)) {
+    var jsIterator;
+    if (_isKeys) {
+      jsIterator = JS('var', '#.keys()', _map._map);
+    } else {
+      jsIterator = JS('var', '#.values()', _map._map);
+    }
+    int modifications = _map.modifications;
+    while (true) {
+      var next = JS('var', '#.next()', jsIterator);
+      bool done = JS('bool', '#.done', next);
+      if (done) break;
+      var value = JS('var', '#.value', next);
+      f(value);
+      if (modifications != _map.modifications) {
+        throw new ConcurrentModificationError(_map);
+      }
+    }
+  }
+}
+
+class _Es6MapIterator<E> implements Iterator<E> {
+  final _map;
+  final int _modifications;
+  final bool _isKeys;
+  var _jsIterator;
+  var _next;
+  E _current;
+
+  _Es6MapIterator(this._map, this._modifications, this._isKeys) {
+    if (_isKeys) {
+      _jsIterator = JS('var', '#.keys()', _map._map);
+    } else {
+      _jsIterator = JS('var', '#.values()', _map._map);
+    }
+    _next = JS('var', '#.next()', _jsIterator);
+  }
+
+  E get current => _current;
+
+  bool moveNext() {
+    if (_modifications != _map._modifications) {
+      throw new ConcurrentModificationError(_map);
+    }
+    bool done = JS('bool', '#.done', _next);
+    if (done) {
+      _current = null;
+      return false;
+    } else {
+      _current = JS('var', '#.value', _next);
+      _next = JS('var', '#.next()', _jsIterator);
+      return true;
+    }
+  }
+}
+
 // TODO(floitsch): use ES6 maps when available.
 class _LinkedCustomHashMap<K, V> extends JsLinkedHashMap<K, V> {
   final _Equality<K> _equals;
   final _Hasher<K> _hashCode;
   final _Predicate _validKey;
 
   _LinkedCustomHashMap(this._equals, this._hashCode,
                        bool validKey(potentialKey))
       : _validKey = (validKey != null) ? validKey : ((v) => v is K);
 
@@ skipping 897 matching lines @@
     } else if (_cell == null) {
       _current = null;
       return false;
     } else {
       _current = _cell._element;
       _cell = _cell._next;
       return true;
     }
   }
 }