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// Copyright (c) 2011, 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.
/// @assertion factory StreamTransformer(StreamSubscription<T>
/// transformer(Stream<S> stream, bool cancelOnError))
/// Creates a StreamTransformer.
/// The returned instance takes responsibility of implementing (bind). When
/// the user invokes bind it returns a new "bound" stream. Only when the user
/// starts listening to the bound stream, the listen method invokes the given
/// closure transformer.
/// @description Checks that [transformer] closure is not invoked until stream
/// is being listened to.
/// @author ilya
import "dart:async";
import "../../../Utils/expect.dart";
main() {
Stream<int> s = new Stream.fromIterable([1]);
StreamTransformer<int, dynamic> tr = new StreamTransformer(
(stream, cancelOnError) {'unexpected call to transformer');
return stream.listen((var x) {});