Language/Expressions/Function_Invocation/async_generator_invokation_t03.dart

  // 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.

/**
 * @assertion If f is marked async*, then a fresh instance s implementing
 * the built-in class Stream is associated with the invocation and
 * immediately returned. When s is listened to, execution of the body of f will
 * begin. When f terminates:
 *   • If the current return value is defined then, if s has been canceled
 *   then its cancellation future is completed with null.
 *   • If the current exception x is defined:
 *     – x is added to s.
 *     – If s has been canceled then its cancellation future is completed with
 *     x as an error.
 *   • s is closed.
 *
 * @description Check that body of async generator function is executed only
 * after Stream instance s is listened.
 *
 * @author a.semenov@unipro.ru
 * @issue 42220
 */
import 'dart:async';
import '../../../Utils/expect.dart';

bool bodyExecuted = false;

Stream generator() async* {
  bodyExecuted = true;
  yield 1;
}

main() {
  asyncStart();
  Stream stream = generator();
  Expect.isFalse(bodyExecuted);
  stream.listen((v) {
    Expect.isTrue(bodyExecuted);
    asyncEnd();
  });
}