// 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 final E first
/// Throws a StateError if this is empty. Otherwise returns the first element in
/// the iteration order, equivalent to this.elementAt(0).
/// @description Checks that a StateError is thrown if queue is empty.
/// @author kaigorodov

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

main() {
  DoubleLinkedQueue queue = new DoubleLinkedQueue();
  
  Expect.throws(() { queue.first; }, (e) => e is StateError);
  
  queue.addFirst(1);
  queue.addFirst(2);
  queue.clear();
  
  Expect.throws(() { queue.first; }, (e) => e is StateError);
}