Change Future.delayed to take a Duration.

sdk/lib/async/future.dart

 // Copyright (c) 2012, 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 dart.async;
 
 /**
  * A [Future] represents a delayed computation. It is used to obtain a not-yet
  * available value, or error, sometime in the future.  Receivers of a
  * [Future] can register callbacks that handle the value or error once it is
@@ skipping 119 matching lines @@
    *
    * See [Completer] to create a Future and complete it later.
    */
   factory Future.immediateError(var error, [Object stackTrace]) {
     return new _FutureImpl<T>.immediateError(error, stackTrace);
   }
 
   /**
    * Creates a future that completes after a delay.
    *
-   * The future will be completed after [milliseconds] have passed with
-   * the result of calling [value]. If [milliseconds] is 0, it completes at the
-   * earliest in the next event-loop iteration.
+   * The future will be completed after the given [duration] has passed with
+   * the result of calling [computation]. If the duration is 0 or less, it
+   * completes no sooner than in the next event-loop iteration.
    *
-   * If calling [value] throws, the created future will complete with the
+   * If [computation] is not given or [:null:] then it will behave as if
+   * [computation] was set to [:() => null:]. That is, it will complete with
+   * [:null:].
+   *
+   * If calling [computation] throws, the created future will complete with the
    * error.
    *
    * See [Completer]s, for futures with values that are computed asynchronously.
+   *
+   * *Deprecation note*: this method initially took an [int] as argument (the
+   * milliseconds to wait). It is now a [Duration].
    */
-  factory Future.delayed(int milliseconds, T value()) {
+  factory Future.delayed(var duration, [T computation()]) {
+    // TODO(floitsch): no need to allocate a ThenFuture when the computation is
+    // null.
+    if (computation == null) computation = (() => null);
     _ThenFuture<dynamic, T> future =
-        new _ThenFuture<dynamic, T>((_) => value());
-    new Timer(milliseconds, (_) => future._sendValue(null));
+        new _ThenFuture<dynamic, T>((_) => computation());
+    new Timer(duration, () => future._sendValue(null));
     return future;
   }
 
   /**
    * Wait for all the given futures to complete and collect their values.
    *
    * Returns a future which will complete once all the futures in a list are
    * complete. If any of the futures in the list completes with an error,
    * the resulting future also completes with an error. Otherwise the value
    * of the returned future will be a list of all the values that were produced.
@@ skipping 183 matching lines @@
    * The argument [exception] should not be `null`.
    *
    * If [exception] is an [AsyncError], it is used directly as the error
    * message sent to the future's listeners, and [stackTrace] is ignored.
    *
    * Otherwise the [exception] and an optional [stackTrace] is combined into an
    * [AsyncError] and sent to this future's listeners.
    */
   void completeError(Object exception, [Object stackTrace]);
 }