Implement Model-Driven-Views spec for Dart

pkg/observe/lib/src/observable_box.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.
+
+part of observe;
+
+/**
+ * An observable box that holds a value. Use this if you want to store a single
+ * value. For other cases, it is better to use [ObservableList],
+ * [ObservableMap], or a custom [Observable] implementation based on
+ * [ObservableMixin]. The field name for changes is "value".
+ */
+class ObservableBox<T> extends ObservableBase {
+  static const _VALUE = const Symbol('value');
+
+  T _value;
+
+  ObservableBox([T initialValue]) : _value = initialValue;
+
+  T get value => _value;
+
+  void set value(T newValue) {
+    _value = notifyField(_VALUE, _value, newValue);
+  }
+
+  String toString() => '#<$runtimeType value: $value>';
+
+  getValueWorkaround(key) {
+    if (key == _VALUE) return value;
+    return null;
+  }
+  void setValueWorkaround(key, newValue) {
+    if (key == _VALUE) value = newValue;
+  }
+}