| // 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 Future<T> firstWhere ( |
| /// bool test(T element), {@deprecated dynamic defaultValue(), T orElse()}) |
| /// |
| /// Finds the first element of this stream matching test. |
| /// |
| /// Returns a future that is completed with the first element of this stream that |
| /// test returns true for. |
| /// |
| /// If no such element is found before this stream is done, and a orElse function |
| /// is provided, the result of calling orElse becomes the value of the future. If |
| /// orElse throws, the returned future is completed with that error. |
| /// |
| /// If this stream emits an error before the first matching element, the returned |
| /// future is completed with that error, and processing stops. |
| /// |
| /// Stops listening to the stream after the first matching element or error has |
| /// been received. |
| /// |
| /// Internally the method cancels its subscription after the first element that |
| /// matches the predicate. This means that single-subscription (non-broadcast) |
| /// streams are closed and cannot be reused after a call to this method. |
| /// |
| /// If an error occurs, or if this stream ends without finding a match and with |
| /// no orElse function provided, the returned future is completed with an error. |
| /// |
| /// The defaultValue parameter is deprecated, and orElse should be used instead. |
| /// @description Checks that if this stream ends without finding a match and an |
| /// orElse function is provided, then the result of calling orElse becomes |
| /// the value of the future. |
| /// @author kaigorodov |
| |
| library firstWhere_A02_t01; |
| import "dart:async"; |
| import "../../../Utils/expect.dart"; |
| |
| void check<T>(Stream<T> s, bool test(T element), T expected) { |
| AsyncExpect.value(expected, s.firstWhere(test, orElse: () => expected)); |
| } |
| |
| void test(CreateStreamFunction create) { |
| check(create([]), (element) => true, 1); |
| check(create<int?>([1, 2, 3]), (int? element) => element == null, null); |
| check(create(new Iterable.generate(0, (int index) => index)), |
| (int element) => false, 0); |
| check(create(new Iterable.generate(0, (int index) => index)), |
| (int element) => true, 0); |
| check(create(new Iterable.generate(10, (int index) => index)), |
| (int element) => false, 22); |
| check(create(new Iterable.generate(10, (int index) => index * 5)), |
| (int element) => element < 0, 33); |
| } |