Language/Classes/Abstract_Instance_Members/override_not_a_subtype_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.

/**
 * @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 return type of
 * an abstract method m1 is not assignable to the return type of non-abstract m2
 * (parameters of both methods being completely identical).
 * @author rodionov
 */

class A {
  int foo(var x) => 42;
}

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

class C extends B {
  String foo(var x) => "";
}

main() {
  new C().foo(2);
}