Update charted to 0.4.8 and roll

packages/observe/lib/src/observer_transform.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 observe.src.observer_transform;
-
-import 'package:observe/observe.dart';
-
-/// ObserverTransform is used to dynamically transform observed value(s).
-///
-///    var obj = new ObservableBox(10);
-///    var observer = new PathObserver(obj, 'value');
-///    var transform = new ObserverTransform(observer,
-///        (x) => x * 2, setValue: (x) => x ~/ 2);
-///
-///    // Open returns the current value of 20.
-///    transform.open((newValue) => print('new: $newValue'));
-///
-///    obj.value = 20; // prints 'new: 40' async
-///    new Future(() {
-///      transform.value = 4; // obj.value will be 2
-///    });
-///
-/// ObserverTransform can also be used to reduce a set of observed values to a
-/// single value:
-///
-///    var obj = new ObservableMap.from({'a': 1, 'b': 2, 'c': 3});
-///    var observer = new CompoundObserver()
-///      ..addPath(obj, 'a')
-///      ..addPath(obj, 'b')
-///      ..addPath(obj, 'c');
-///
-///    var transform = new ObserverTransform(observer,
-///        (values) => values.fold(0, (x, y) => x + y));
-///
-///    // Open returns the current value of 6.
-///    transform.open((newValue) => print('new: $newValue'));
-///
-///    obj['a'] = 2;
-///    obj['c'] = 10; // will print 'new 14' asynchronously
-///
-class ObserverTransform extends Bindable {
-  Bindable _bindable;
-  Function _getTransformer, _setTransformer;
-  Function _notifyCallback;
-  var _value;
-
-  ObserverTransform(Bindable bindable, computeValue(value), {setValue(value)})
-      : _bindable = bindable,
-        _getTransformer = computeValue,
-        _setTransformer = setValue;
-
-  open(callback) {
-    _notifyCallback = callback;
-    _value = _getTransformer(_bindable.open(_observedCallback));
-    return _value;
-  }
-
-  _observedCallback(newValue) {
-    final value = _getTransformer(newValue);
-    if (value == _value) return null;
-    _value = value;
-    return _notifyCallback(value);
-  }
-
-  void close() {
-    if (_bindable != null) _bindable.close();
-    _bindable = null;
-    _getTransformer = null;
-    _setTransformer = null;
-    _notifyCallback = null;
-    _value = null;
-  }
-
-  get value => _value = _getTransformer(_bindable.value);
-
-  set value(newValue) {
-    if (_setTransformer != null) {
-      newValue = _setTransformer(newValue);
-    }
-    _bindable.value = newValue;
-  }
-
-  deliver() => _bindable.deliver();
-}