Language/Types/Interface_Types/subtype_t10.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 A type T is more specific than a type S, written T << S, if one
/// of the following conditions is met:
///  • T is S.
///  • T is ⊥
///  • S is dynamic.
///  • S is a direct supertype of T.
///  • T is a type parameter and S is the upper bound of T.
///  • T is a type parameter and S is Object.
///  • T is of the form I<T1, ..., Tn > and S is of the form I <S1, ..., Sn>
///    and Ti << Si 1 <= i <= n.
///  • T and S are both function types, and T << S under the rules of section
///    (Types/Function Types).
///  • T is a function type and S is Function.
///  • T << U and U << S.
/// << is a partial order on types. T is a subtype of S, written T <: S, iff
/// [⊥/Dynamic]T << S.
/// . . .
/// An interface type T may be assigned to a type S, written T <=> S, if either
/// T <: S or S <: T.
/// @description Checks that an interface type may be assigned to its supertype.
/// @author iefremov

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


class I {}

class A implements I {}

class B extends A {}

class C {}

class Checker<S> {
  Checker() {}

  check(dynamic t) {
    Expect.isTrue(t is S);
    S ss = t;
  }
}

main() {
  new Checker<num>().check(1);
  new Checker<num>().check(1.0);
  new Checker<A>().check(new B());
  new Checker<Object>().check(new C());
  new Checker<I>().check(new A());
}