| // Copyright (c) 2022, 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'; |
| |
| class _WhereTypeStreamSink<S, T> implements EventSink<S> { |
| final EventSink<T> _sink; |
| |
| _WhereTypeStreamSink(this._sink); |
| |
| @override |
| void add(S data) { |
| if (data is T) { |
| _sink.add(data); |
| } |
| } |
| |
| @override |
| void addError(e, [StackTrace? stackTrace]) => _sink.addError(e, stackTrace); |
| |
| @override |
| void close() => _sink.close(); |
| } |
| |
| class _WhereTypeStreamTransformer<S, T> extends StreamTransformerBase<S, T> { |
| @override |
| Stream<T> bind(Stream<S> stream) => Stream.eventTransformed( |
| stream, (sink) => _WhereTypeStreamSink<S, T>(sink)); |
| } |
| |
| extension StreamExtension<T> on Stream<T> { |
| Stream<S> whereType<S>() => transform(_WhereTypeStreamTransformer<T, S>()); |
| } |