Add Future.any and Stream.fromFutures.

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;
 
 /**
  * An object representing a delayed computation.
  *
  * A [Future] is used to represent a potential value, or error,
@@ skipping 299 matching lines @@
       }, onError: handleError);
     }
     if (remaining == 0) {
       return new Future.value(const []);
     }
     values = new List(remaining);
     return result;
   }
 
   /**
+   * Returns the result of the first future in [futures] to complete.
+   *
+   * The returned future is completed with the result of the first
+   * future in [futures] to report that it is complete.
+   * The results of all the other futures are discarded.
+   *
+   * If [futures] is empty, or if none of its futures complete,
+   * the returned future never completes.
+   */
+  static Future/*<T>*/ any/*<T>*/(Iterable<Future/*<T>*/> futures) {
+    var completer = new Completer.sync();
+    var onValue = (value) {
+      if (!completer.isCompleted) completer.complete(value);
+    };
+    var onError = (error, stack) {
+      if (!completer.isCompleted) completer.completeError(error, stack);
+    };
+    for (var future in futures) {
+      future.then(onValue, onError: onError);
+    }
+    return completer.future;
+  }
+
+
+  /**
    * Perform an async operation for each element of the iterable, in turn.
    *
    * Runs [f] for each element in [input] in order, moving to the next element
    * only when the [Future] returned by [f] completes. Returns a [Future] that
    * completes when all elements have been processed.
    *
    * The return values of all [Future]s are discarded. Any errors will cause the
    * iteration to stop and will be piped through the returned [Future].
    *
    * If [f] returns a non-[Future], iteration continues immediately. Otherwise
@@ skipping 390 matching lines @@
   if (replacement != null) {
     error = _nonNullError(replacement.error);
     stackTrace = replacement.stackTrace;
   }
   result._completeError(error, stackTrace);
 }
 
 /** Helper function that converts `null` to a [NullThrownError]. */
 Object _nonNullError(Object error) =>
   (error != null) ? error : new NullThrownError();