LibTest/async/StreamIterator/cancel_A01_t01.dart

// 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.

// @dart = 2.9

/// @assertion Future cancel()
/// Cancels the stream iterator (and the underlying stream subscription) early.
///
/// The stream iterator is automatically canceled if the moveNext future
/// completes with either false or an error.
///
/// If you need to stop listening for values before the stream iterator is
/// automatically closed, you must call cancel to ensure that the stream is
/// properly closed.
///
/// If moveNext has been called when the iterator is cancelled, its returned
/// future will complete with false as value, as will all further calls to
/// moveNext.
///
/// Returns a future if the cancel-operation is not completed synchronously.
/// Otherwise returns null.
///
/// @description Checks that call to cancel() makes subsequent call to moveNext()
/// complete with false as value.
/// @author kaigorodov


import "dart:async";
import "../../../Utils/expect.dart";

void check(List source, List expected) {
  List actual = new List();
  Stream stream = new Stream.fromIterable(source);
  StreamIterator streamIterator = new StreamIterator(stream);
  asyncStart();
  void step(bool hasNext) {
    if (!hasNext) {
      Expect.listEquals(expected, actual);
      asyncEnd();
      return;
    }
    if (streamIterator.current == null) {
      streamIterator.cancel();
    } else {
      actual.add(streamIterator.current);
    }
    streamIterator.moveNext().then(step);
  }
  streamIterator.moveNext().then(step);
}

main() {
  check([1, 2, 3, "end"], [1, 2, 3, "end"]);
  check([1, 2, null, 3, "end"], [1, 2]);
}