Language/Classes/Abstract_Instance_Members/override_not_a_subtype_t05.dart

// Copyright (c) 2019, 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). Test type aliases
/// @author sgrekhov@unipro.ru

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

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

class C extends BAlias {
  String foo(var x) => "Lily was here";
}

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