| // 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 the assignability (both ways) of variables and values |
| /// that meet the described requirements. |
| |
| |
| class I {} |
| I makeI() => new I(); |
| |
| class A implements I {} |
| A makeA() => new A(); |
| |
| class B extends A {} |
| |
| class C {} |
| Object makeObject() => new Object(); |
| |
| main() { |
| Object o = new C(); |
| Object c = makeObject(); |
| |
| I i = new A(); |
| I a1 = makeI(); |
| |
| A a2 = new B(); |
| A b = makeA(); |
| } |