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| 1 // Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file |
| 2 // for details. All rights reserved. Use of this source code is governed by a |
| 3 // BSD-style license that can be found in the LICENSE file. |
| 4 |
| 5 import 'dart:async'; |
| 6 |
| 7 import 'delegate/stream.dart'; |
| 8 |
| 9 /// Creates a wrapper that coerces the type of [transformer]. |
| 10 /// |
| 11 /// This soundly converts a [StreamTransformer] to a `StreamTransformer<S, T>`, |
| 12 /// regardless of its original generic type, by asserting that the events |
| 13 /// emitted by the transformed stream are instances of `T` whenever they're |
| 14 /// provided. If they're not, the stream throws a [CastError]. |
| 15 StreamTransformer/*<S, T>*/ typedStreamTransformer/*<S, T>*/( |
| 16 StreamTransformer transformer) => |
| 17 transformer is StreamTransformer/*<S, T>*/ |
| 18 ? transformer |
| 19 : new _TypeSafeStreamTransformer(transformer); |
| 20 |
| 21 /// A wrapper that coerces the type of the stream returned by an inner |
| 22 /// transformer. |
| 23 class _TypeSafeStreamTransformer<S, T> implements StreamTransformer<S, T> { |
| 24 final StreamTransformer _inner; |
| 25 |
| 26 _TypeSafeStreamTransformer(this._inner); |
| 27 |
| 28 Stream<T> bind(Stream<S> stream) => |
| 29 DelegatingStream.typed(_inner.bind(stream)); |
| 30 } |
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