Language/Classes/Abstract_Instance_Members/override_not_a_subtype_t03.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.
 */
/**
 * @assertion Unless explicitly stated otherwise, all ordinary rules that apply
 * to methods apply to abstract methods.
 * It is a compile error if an instance method m1 overrides an instance member
 * m2 and the type of m1 is not a subtype of the type of m2.
 * @description Checks that a compile error is produced when the type of an
 * abstract m1 is not a subtype of the non-abstract m2's type because their
 * respective optional positional parameter types are not mutually assignable.
 * @author rodionov
 */

class A {
  foo([int? x]) {}
}

abstract class B extends A {
  foo([String? x]);
//             ^
// [analyzer] unspecified
// [cfe] unspecified
}

class C extends B {
  foo([String? x]) {}
}

main() {
  new A().foo(2);
  new C().foo("1");
}