blob: 2e056b2f6037407e88651f96913dbecb19f4019a [file] [log] [blame]
// 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';
/// A transformer that converts a broadcast stream into a single-subscription
/// stream.
/// This buffers the broadcast stream's events, which means that it starts
/// listening to a stream as soon as it's bound.
/// This also casts the source stream's events to type `T`. If the cast fails,
/// the result stream will emit a [TypeError]. This behavior is deprecated, and
/// should not be relied upon.
class SingleSubscriptionTransformer<S, T> extends StreamTransformerBase<S, T> {
const SingleSubscriptionTransformer();
Stream<T> bind(Stream<S> stream) {
late StreamSubscription<S> subscription;
var controller =
StreamController<T>(sync: true, onCancel: () => subscription.cancel());
subscription = stream.listen((value) {
// TODO(nweiz): When we release a new major version, get rid of the second
// type parameter and avoid this conversion.
try {
controller.add(value as T);
} on TypeError catch (error, stackTrace) {
controller.addError(error, stackTrace);
}, onError: controller.addError, onDone: controller.close);