Add reactive-inspired stream transformers:

lib/src/transformers/debounce.dart

+// Copyright (c) 2016, 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.
+
+import "dart:async";
+import "throttle.dart";

[nweiz, 2016/03/01 02:10:04]

Nit: newline between these two imports.

[Lasse Reichstein Nielsen, 2016/03/01 16:51:17]

Acknowledged.

+
+/// Drops any event that happens shortly after another event.
+///
+/// If an event happens within a certain [Duration] of the previous event,
+/// the new event is dropped from the result stream.
+/// The dropped event will still cause following events to be dropped

[nweiz, 2016/03/01 02:10:04]

Nit: "will still cause" -> "still causes"

[Lasse Reichstein Nielsen, 2016/03/01 16:51:17]

Acknowledged.

+/// until the entire duration has passed without any events.
+///
+/// This differs from [Throttle] which only restarts its timer at events
+/// that aren't dropped.
+///
+/// Any error in the source stream will be forwarded to the transformed stream
+/// and will terminate the transformation.
+class Debounce<S> implements StreamTransformer<S, S> {
+  final Duration _interval;
+  final Function _createStopwatch;
+
+  /// Drops events sooner than [interval] after any other event.
+  ///
+  /// A [createStopwatch] function can be provided to introduce a non-standard
+  /// [Stopwatch] implementation, e.g., for testing

[nweiz, 2016/03/01 02:10:03]

Nit: "testing" -> "testing."

[Lasse Reichstein Nielsen, 2016/03/01 16:51:16]

Acknowledged.

+  /// It defaults to using [StopWatch].

[nweiz, 2016/03/01 02:10:04]

Nit: "StopWatch" -> "Stopwatch"

[Lasse Reichstein Nielsen, 2016/03/01 16:51:16]

Acknowledged.

+  Debounce(Duration interval, {Stopwatch createStopwatch()})

[nweiz, 2016/03/01 02:10:04]

Up to you, but I'd just use the clock package here. It's pretty standard, and
it's a good show of support for community packages to have Dart team packages
use them.

[Lasse Reichstein Nielsen, 2016/03/01 16:51:17]

I don't really like introducing an abstraction layer that is only used for
testing. It's a a kind of implicit dependency injection. This is just being
explicit about it.
I also try to not let packages corresponding to dart: libraries depend on any
other packages - except for testing. If you just use the package, you don't have
any other dependencies.

+      : _interval = interval,
+        _createStopwatch = createStopwatch;
+
+  Stream<S> bind(Stream<S> stream) async* {
+    var interval = Duration.ZERO;  // Avoid dropping the first event.
+    var stopwatch =
+        (_createStopwatch == null) ? new Stopwatch() : _createStopwatch();
+    stopwatch.start() ;
+    await for (var source in stream) {
+      if (stopwatch.elapsed >= interval) {
+        yield source;
+        interval = _interval;
+      }
+      stopwatch.reset();
+    }
+    stopwatch.stop();
+  }
+}