Add CancelableOperation.valueOrCancellation.
R=lrn@google.com
Review URL: https://codereview.chromium.org//1561323002 .
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e7ed4a..6db6f36 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,9 @@
-## 1.4.0
+## 1.6.0
+
+- Added `CancelableOperation.valueOrCancellation()`, which allows users to be
+ notified when an operation is canceled elsewhere.
+
+## 1.5.0
- Added `LazyStream`, which forwards to the return value of a callback that's
only called when the stream is listened to.
diff --git a/lib/src/cancelable_operation.dart b/lib/src/cancelable_operation.dart
index 89889a3..a48c94f 100644
--- a/lib/src/cancelable_operation.dart
+++ b/lib/src/cancelable_operation.dart
@@ -57,6 +57,24 @@
return controller.stream;
}
+ /// Creates a [Future] that completes when this operation completes *or* when
+ /// it's cancelled.
+ ///
+ /// If this operation completes, this completes to the same result as [value].
+ /// If this operation is cancelled, the returned future waits for the future
+ /// returned by [cancel], then completes to [cancellationValue].
+ Future valueOrCancellation([T cancellationValue]) {
+ var completer = new Completer.sync();
+
+ value.then(completer.complete, onError: completer.completeError);
+
+ _completer._cancelMemo.future.then((_) {
+ completer.complete(cancellationValue);
+ }, onError: completer.completeError);
+
+ return completer.future;
+ }
+
/// Cancels this operation.
///
/// This returns the [Future] returned by the [CancelableCompleter]'s
@@ -140,9 +158,12 @@
}
/// Cancel the completer.
- Future _cancel() => _cancelMemo.runOnce(() {
- if (_inner.isCompleted) return null;
- _isCanceled = true;
- if (_onCancel != null) return _onCancel();
- });
+ Future _cancel() {
+ if (_inner.isCompleted) return new Future.value();
+
+ return _cancelMemo.runOnce(() {
+ _isCanceled = true;
+ if (_onCancel != null) return _onCancel();
+ });
+ }
}
diff --git a/pubspec.yaml b/pubspec.yaml
index e98c59e..16e2ea2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
name: async
-version: 1.5.0
+version: 1.6.0-dev
author: Dart Team <misc@dartlang.org>
description: Utility functions and classes related to the 'dart:async' library.
homepage: https://www.github.com/dart-lang/async
diff --git a/test/cancelable_operation_test.dart b/test/cancelable_operation_test.dart
index 189c073..4d8c295 100644
--- a/test/cancelable_operation_test.dart
+++ b/test/cancelable_operation_test.dart
@@ -45,6 +45,16 @@
expect(completer.isCompleted, isTrue);
});
+ test("sends values to valueOrCancellation", () {
+ expect(completer.operation.valueOrCancellation(), completion(equals(1)));
+ completer.complete(1);
+ });
+
+ test("sends errors to valueOrCancellation", () {
+ expect(completer.operation.valueOrCancellation(), throwsA("error"));
+ completer.completeError("error");
+ });
+
group("throws a StateError if completed", () {
test("successfully twice", () {
completer.complete(1);
@@ -168,6 +178,38 @@
completer.complete(1);
expect(() => completer.complete(1), throwsStateError);
});
+
+ test("fires valueOrCancellation with the given value", () {
+ var completer = new CancelableCompleter();
+ expect(completer.operation.valueOrCancellation(1), completion(equals(1)));
+ completer.operation.cancel();
+ });
+
+ test("pipes an error through valueOrCancellation", () {
+ var completer = new CancelableCompleter(onCancel: () {
+ throw "error";
+ });
+ expect(completer.operation.valueOrCancellation(1), throwsA("error"));
+ completer.operation.cancel();
+ });
+
+ test("valueOrCancellation waits on the onCancel future", () async {
+ var innerCompleter = new Completer();
+ var completer = new CancelableCompleter(onCancel: () => innerCompleter.future);
+
+ var fired = false;
+ completer.operation.valueOrCancellation().then((_) {
+ fired = true;
+ });
+
+ completer.operation.cancel();
+ await flushMicrotasks();
+ expect(fired, isFalse);
+
+ innerCompleter.complete();
+ await flushMicrotasks();
+ expect(fired, isTrue);
+ });
});
group("asStream()", () {
