LanguageFeatures/Super-mixins/covariance_t04.dart

// Copyright (c) 2018, 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 In a mixin declaration like
/// mixin A<X extends S, Y extends T> on B, C implements D, E { body }
/// the on clause declares the interfaces B and C as super-class constraints of
/// the mixin. Having a super-class constaint allows the mixin declaration
/// instance members to perform super-invocations (like super.foo()) if they are
/// allowed by a class implementing both B and C. The mixin introduced by A can
/// then only be applied to classes that implement both B and C.
///
/// @description Checks that it is a compile error if mixin is applied to the
/// class which doesn't implement required interface
/// @author sgrekhov@unipro.ru

class A {
  covariant num number = 0;
}

class B {
  int number = 1;
}

mixin M on A {
  test() {
    super.number = 3;
  }
}

class MA extends B with M {}
//    ^
// [analyzer] unspecified
// [cfe] unspecified

main() {
  new MA().test();
}