Add AsyncMemoizer.future.

lib/src/async_memoizer.dart

 // Copyright (c) 2015, 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 async.async_memoizer;
 
 import 'dart:async';
 
 /// A class for running an asynchronous function exactly once and caching its
 /// result.
@@ skipping 13 matching lines @@
 ///   final _closeMemo = new AsyncMemoizer();
 ///
 ///   Future close() => _closeMemo.runOnce(() {
 ///     // ...
 ///   });
 /// }
 /// ```
 class AsyncMemoizer<T> {
   /// The future containing the method's result.
   ///
-  /// This will be `null` if [run] hasn't been called yet.
-  Future<T> _future;
+  /// This can be accessed at any time, and will fire once [runOnce] is called.
+  Future<T> get future => _completer.future;
+  final _completer = new Completer();

[kevmoo, 2015/09/03 11:58:33]

Completer<T>

 
   /// Whether [run] has been called yet.
-  bool get hasRun => _future != null;
+  bool get hasRun => _completer.isCompleted;
 
   /// Runs the function, [computation], if it hasn't been run before.
   ///
   /// If [run] has already been called, this returns the original result.
   Future<T> runOnce(computation()) {
-    if (_future == null) _future = new Future.sync(computation);
-    return _future;
+    if (!hasRun) _completer.complete(new Future.sync(computation));

[kevmoo, 2015/09/03 11:58:33]

new Future<T> ?

+    return future;
   }
 }