Index: packages/async/lib/src/typed_stream_transformer.dart |
diff --git a/packages/async/lib/src/typed_stream_transformer.dart b/packages/async/lib/src/typed_stream_transformer.dart |
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index 0000000000000000000000000000000000000000..98d5e706a7363c951fc4668af310b57a6ed6cac5 |
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+++ b/packages/async/lib/src/typed_stream_transformer.dart |
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+// 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 'delegate/stream.dart'; |
+ |
+/// Creates a wrapper that coerces the type of [transformer]. |
+/// |
+/// This soundly converts a [StreamTransformer] to a `StreamTransformer<S, T>`, |
+/// regardless of its original generic type, by asserting that the events |
+/// emitted by the transformed stream are instances of `T` whenever they're |
+/// provided. If they're not, the stream throws a [CastError]. |
+StreamTransformer<S, T> typedStreamTransformer<S, T>( |
+ StreamTransformer transformer) => |
+ transformer is StreamTransformer<S, T> |
+ ? transformer |
+ : new _TypeSafeStreamTransformer(transformer); |
+ |
+/// A wrapper that coerces the type of the stream returned by an inner |
+/// transformer. |
+class _TypeSafeStreamTransformer<S, T> implements StreamTransformer<S, T> { |
+ final StreamTransformer _inner; |
+ |
+ _TypeSafeStreamTransformer(this._inner); |
+ |
+ Stream<T> bind(Stream<S> stream) => |
+ DelegatingStream.typed(_inner.bind(stream)); |
+} |