Add an AsyncThunk class.

lib/src/future_group.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.future_group;
 
 import 'dart:async';
 
 /// A collection of futures waits until all added [Future]s complete.
 ///
 /// Futures are added to the group with [add]. Once you're finished adding
 /// futures, signal that by calling [close]. Then, once all added futures have
 /// completed, [future] will complete with a list of values from the futures in
 /// the group, in the order they were added.
 ///
 /// If any added future completes with an error, [future] will emit that error
 /// and the group will be closed, regardless of the state of other futures in
 /// the group.
 ///
 /// This is similar to [Future.wait] with `eagerError` set to `true`, except
 /// that a [FutureGroup] can have futures added gradually over time rather than
 /// needing them all at once.
 class FutureGroup<T> implements Sink<Future<T>> {
   /// The number of futures that have yet to complete.
+  int get pending => _pending;

[Lasse Reichstein Nielsen, 2015/07/02 12:25:58]

Unrelated change?

[nweiz, 2015/07/06 21:04:16]

Done.

   var _pending = 0;
 
   /// Whether [close] has been called.
   var _closed = false;
 
   /// The future that fires once [close] has been called and all futures in the
   /// group have completed.
   ///
   /// This will also complete with an error if any of the futures in the group
   /// fails, regardless of whether [close] was called.
@@ skipping 33 matching lines @@
   /// Signals to the group that the caller is done adding futures, and so
   /// [future] should fire once all added futures have completed.
   void close() {
     _closed = true;
     if (_pending != 0) return;
     if (_completer.isCompleted) return;
     _completer.complete(_values);
   }
 }