implement dirty checking for @observable objects

pkg/observe/lib/src/to_observable.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;
+
+/**
+ * Converts the [Iterable] or [Map] to an [ObservableList] or [ObservableMap],
+ * respectively. This is a convenience function to make it easier to convert
+ * literals into the corresponding observable collection type.
+ *
+ * If [value] is not one of those collection types, or is already [Observable],
+ * it will be returned unmodified.
+ *
+ * If [value] is a [Map], the resulting value will use the appropriate kind of
+ * backing map: either [HashMap], [LinkedHashMap], or [SplayTreeMap].
+ *
+ * By default this performs a deep conversion, but you can set [deep] to false
+ * for a shallow conversion. This does not handle circular data structures.
+ * If a conversion is peformed, mutations are only observed to the result of
+ * this function. Changing the original collection will not affect it.
+ */
+// TODO(jmesserly): ObservableSet?
+toObservable(value, {bool deep: true}) =>
+    deep ? _toObservableDeep(value) : _toObservableShallow(value);
+
+_toObservableShallow(value) {
+  if (value is Observable) return value;
+  if (value is Map) return new ObservableMap.from(value);
+  if (value is Iterable) return new ObservableList.from(value);
+  return value;
+}
+
+_toObservableDeep(value) {
+  if (value is Observable) return value;
+  if (value is Map) {
+    var result = new ObservableMap._createFromType(value);
+    value.forEach((k, v) {
+      result[_toObservableDeep(k)] = _toObservableDeep(v);
+    });
+    return result;
+  }
+  if (value is Iterable) {
+    return new ObservableList.from(value.map(_toObservableDeep));
+  }
+  return value;
+}