Language/Types/Interface_Types/subtype_t13.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 this statement is true for a parameterized type
 * extending other parameterized type with the same type parameter.
 * @author iefremov
 */
import "../../../Utils/expect.dart";

class G<T> {}
class Generic<T> extends G<T> {}

// these produce the required static type for static checker
// but won't fail at run time because they return null after all
G? makeG() {}
G<int>? makeGint() {}
G<Object>? makeGObject() {}

main() {
  Expect.isTrue(new Generic() is G);
  G g = new Generic();
  G? g_ = makeG();

  Expect.isTrue(new Generic<int>() is G<int>);
  G<int> g2 = new Generic<int>();
  G<int>? g2_ = makeGint();

  Expect.isTrue(new Generic<Object>() is G<Object>);
  G<Object> g3 = new Generic<Object>();
  G<Object>? g3_ = makeGObject();
}