Support for observable models, fixes #259

lib/observe/map.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.
+
+library web_ui.observe.map;
+
+import 'dart:collection';
+import 'package:web_ui/observe.dart';
+import 'list.dart';
+
+typedef Map<K, dynamic> MapFactory<K>();
+
+// TODO(jmesserly): this needs to be faster. We currently require multiple
+// lookups per key to get the old value. Most likely this needs to be based on
+// a modified HashMap source code.
+/**
+ * Represents an observable map of model values. If any items are added,
+ * removed, or replaced, then observers that are registered with
+ * [observe] will be notified.
+ */
+class ObservableMap<K, V> implements Map<K, V> {
+  final Map<K, V> _map;
+  final Map<K, Object> _observeKey;
+  Object _observeLength;
+  _ObservableMapKeyIterable<K, V> _keys;
+  _ObservableMapValueIterable<K, V> _values;
+
+  /**
+   * Creates an observable map, optionally using the provided factory
+   * [createMap] to construct a custom map type.
+   */
+  ObservableMap({MapFactory<K> createMap})
+      : _map = createMap != null ? createMap() : new Map<K, V>(),
+        _observeKey = createMap != null ? createMap() : new Map<K, Object>() {
+    _keys = new _ObservableMapKeyIterable<K, V>(this);
+    _values = new _ObservableMapValueIterable<K, V>(this);
+  }
+
+  /** Creates a new observable map using a [LinkedHashMap]. */
+  ObservableMap.linked() : this(createMap: () => new LinkedHashMap());
+
+  /**
+   * Creates an observable map that contains all key value pairs of [other].
+   */
+  factory ObservableMap.from(Map<K, V> other, {MapFactory<K> createMap}) {
+    var result = new ObservableMap<K, V>(createMap: createMap);
+    other.forEach((K key, V value) { result[key] = value; });
+    return result;
+  }
+
+
+  Iterable<K> get keys => _keys;
+
+  Iterable<V> get values => _values;
+
+  int get length {
+    _notifyReadLength();
+    return _map.length;
+  }
+
+  bool get isEmpty => length == 0;
+
+  void _notifyReadKey(K key) {
+    if (observeReads) _observeKey[key] = notifyRead(_observeKey[key]);
+  }
+
+  void _notifyReadLength() {
+    if (observeReads) _observeLength = notifyRead(_observeLength);
+  }
+
+  void _notifyReadAll() {
+    if (!observeReads) return;
+    _observeLength = notifyRead(_observeLength);
+    for (K key in _map.keys) {
+      _observeKey[key] = notifyRead(_observeKey[key]);
+    }
+  }
+
+  void _notifyWriteLength(int originalLength) {
+    if (_observeLength != null && originalLength != _map.length) {
+      _observeLength = notifyWrite(_observeLength);
+    }
+  }
+
+  void _notifyWriteKey(K key) {
+    var observer = _observeKey.remove(key);
+    if (observer != null) notifyWrite(observer);
+  }
+
+  bool containsValue(V value) {
+    _notifyReadAll();
+    return _map.containsValue(value);
+  }
+
+  bool containsKey(K key) {
+    _notifyReadKey(key);
+    return _map.containsKey(key);
+  }
+
+  V operator [](K key) {
+    _notifyReadKey(key);
+    return _map[key];
+  }
+
+  void operator []=(K key, V value) {
+    int len = _map.length;
+    V oldValue = _map[key];
+    _map[key] = value;
+    if (len != _map.length || oldValue != value) {
+      _notifyWriteKey(key);
+      _notifyWriteLength(len);

[Siggi Cherem (dart-lang), 2013/02/13 01:43:24]

should this be separate? I mean,

if (oldValue != value) _notifyWriteKey(key);
if (len != map.length) _notifyWriteLengh(len);

[Jennifer Messerly, 2013/02/13 05:43:15]

Not quite, it was a bit tricky to get right. Added comment:

    // Note: if length changed, it means the key was added, so we need to
    // _notifyWriteKey. Also _notifyWriteLength will check if length changed.

[Siggi Cherem (dart-lang), 2013/02/13 19:28:54]

I see, so basically you are handling when the value is 'null'.

I was also thinking that we don't want to notify write on 'length' when you are
just replacing the value, though. Maybe it should be more like this?
   if (oldValue != value || len != map.length) _notifyWriteKey(key);
   if (len != map.length) _notifyWriteLengh(len);

[Jennifer Messerly, 2013/02/13 20:21:20]

Uh, as I said in comment, _notifyWriteLength will check length. We do not need
another check. I can walk you through the code in person if it helps, it's
possible I'm just really confused :)

[Siggi Cherem (dart-lang), 2013/02/13 20:41:13]

My bad, I don't know how but I managed to completely ignore the second sentence
of your comment and missed entirely that it was being checked in
notifyWriteLength.... sorry for all the confusion.

+    }
+  }
+
+  V putIfAbsent(K key, V ifAbsent()) {
+    // notifyRead because result depends on if the key already exists
+    _notifyReadKey(key);
+
+    int len = _map.length;
+    V result = _map.putIfAbsent(key, ifAbsent);
+    if (len != _map.length) {
+      _notifyWriteKey(key);
+      _notifyWriteLength(len);
+    }
+    return result;
+  }
+
+  V remove(K key) {
+    // notifyRead because result depends on if the key already exists
+    _notifyReadKey(key);
+
+    int len = _map.length;
+    V result =  _map.remove(key);
+    if (len != _map.length) {
+      _notifyWriteKey(key);
+      _notifyWriteLength(len);
+    }
+    return result;
+  }
+
+  void clear() {
+    int len = _map.length;
+    _map.clear();
+    _notifyWriteLength(len);
+    _observeKey.values.forEach(notifyWrite);
+    _observeKey.clear();
+  }
+
+  void forEach(void f(K key, V value)) {
+    _notifyReadAll();
+    _map.forEach(f);
+  }
+
+  String toString() => Maps.mapToString(this);
+}
+
+class _ObservableMapKeyIterable<K, V> extends Iterable<K> {
+  final ObservableMap<K, V> _map;
+  _ObservableMapKeyIterable(this._map);
+
+  Iterator<K> get iterator => new _ObservableMapKeyIterator<K, V>(_map);
+}
+
+class _ObservableMapKeyIterator<K, V> implements Iterator<K> {
+  final ObservableMap<K, V> _map;
+  final Iterator<K> _keys;
+
+  _ObservableMapKeyIterator(ObservableMap<K, V> map)
+      : _map = map,
+        _keys = map._map.keys.iterator;
+
+  bool moveNext() {
+    _map._notifyReadLength();
+    return _keys.moveNext();
+  }
+
+  K get current {
+    var key = _keys.current;
+    if (key != null) _map._notifyReadKey(key);
+    return key;
+  }
+}
+
+
+class _ObservableMapValueIterable<K, V> extends Iterable<V> {
+  final ObservableMap<K, V> _map;
+  _ObservableMapValueIterable(this._map);
+
+  Iterator<V> get iterator => new _ObservableMapValueIterator<K, V>(_map);
+}
+
+class _ObservableMapValueIterator<K, V> implements Iterator<V> {
+  final ObservableMap<K, V> _map;
+  final Iterator<K> _keys;
+  final Iterator<V> _values;
+
+  _ObservableMapValueIterator(ObservableMap<K, V> map)
+      : _map = map,
+        _keys = map._map.keys.iterator,
+        _values = map._map.values.iterator;
+
+  bool moveNext() {
+    _map._notifyReadLength();
+    bool moreKeys = _keys.moveNext();
+    bool moreValues = _values.moveNext();
+    if (moreKeys != moreValues) {
+      throw new StateError('keys and values should be the same length');
+    }
+    return moreValues;
+  }
+
+  V get current {
+    var key = _keys.current;
+    if (key != null) _map._notifyReadKey(key);
+    return _values.current;
+  }
+}