Update charted to 0.4.8 and roll

packages/observable/lib/src/observable.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.
+
+library observable.src.observable;
+
+import 'dart:async';
+import 'dart:collection' show UnmodifiableListView;
+
+import 'package:meta/meta.dart';
+
+import 'change_record.dart' show ChangeRecord;
+import 'property_change_record.dart' show PropertyChangeRecord;
+
+/// Represents an object with observable properties. This is used by data in
+/// model-view architectures to notify interested parties of [changes] to the
+/// object's properties (fields or getter/setter pairs).
+///
+/// The interface does not require any specific technique to implement
+/// observability. You can implement it in the following ways:
+///
+/// - Deriving from this class via a mixin or base class. When a field,
+///   property, or indexable item is changed, the derived class should call
+///   [notifyPropertyChange]. See that method for an example.
+/// - Implementing this interface and providing your own implementation.
+abstract class Observable {
+  StreamController<List<ChangeRecord>> _changes;
+
+  List<ChangeRecord> _records;
+
+  /// The stream of property change records to this object, delivered
+  /// asynchronously.
+  ///
+  /// [deliverChanges] can be called to force synchronous delivery.
+  Stream<List<ChangeRecord>> get changes {
+    if (_changes == null) {
+      _changes = new StreamController.broadcast(
+          sync: true, onListen: observed, onCancel: unobserved);
+    }
+    return _changes.stream;
+  }
+
+  /// Derived classes may override this method to be called when the [changes]
+  /// are first observed.
+  // TODO(tvolkert): @mustCallSuper (github.com/dart-lang/sdk/issues/27275)
+  @protected
+  void observed() {}
+
+  /// Derived classes may override this method to be called when the [changes]
+  /// are no longer being observed.
+  // TODO(tvolkert): @mustCallSuper (github.com/dart-lang/sdk/issues/27275)
+  @protected
+  void unobserved() {
+    // Free some memory
+    _changes = null;
+  }
+
+  /// True if this object has any observers.
+  bool get hasObservers => _changes != null && _changes.hasListener;
+
+  /// Synchronously deliver pending [changes].
+  ///
+  /// Returns `true` if any records were delivered, otherwise `false`.
+  /// Pending records will be cleared regardless, to keep newly added
+  /// observers from being notified of changes that occurred before
+  /// they started observing.
+  bool deliverChanges() {
+    List<ChangeRecord> records = _records;
+    _records = null;
+    if (hasObservers && records != null) {
+      _changes.add(new UnmodifiableListView<ChangeRecord>(records));
+      return true;
+    }
+    return false;
+  }
+
+  /// Notify that the [field] name of this object has been changed.
+  ///
+  /// The [oldValue] and [newValue] are also recorded. If the two values are
+  /// equal, no change will be recorded.
+  ///
+  /// For convenience this returns [newValue].
+  /*=T*/ notifyPropertyChange/*<T>*/(
+      Symbol field, /*=T*/ oldValue, /*=T*/ newValue) {
+    if (hasObservers && oldValue != newValue) {
+      notifyChange(new PropertyChangeRecord(this, field, oldValue, newValue));
+    }
+    return newValue;
+  }
+
+  /// Notify observers of a change.
+  ///
+  /// This will automatically schedule [deliverChanges].
+  ///
+  /// For most objects [Observable.notifyPropertyChange] is more convenient, but
+  /// collections sometimes deliver other types of changes such as a
+  /// [MapChangeRecord].
+  void notifyChange(ChangeRecord record) {
+    if (!hasObservers) return;
+    if (_records == null) {
+      _records = [];
+      scheduleMicrotask(deliverChanges);
+    }
+    _records.add(record);
+  }
+}