Language/Types/Interface_Types/subtype_t05.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 null (the only value of type ⊥) may be assigned to
 * any nullable variable.
 * @author iefremov
 */

class A {}

abstract class I {}

typedef t1();
typedef void t2();
typedef List t3(List<int>? l, [Map<List, List<Map>>? m]);

main() {
  var x = null;
  int? i = null;
  Object? o = null;
  String? s = null;
  bool? b = null;
  List? l = null;
  List<int>? l1 = null;
  List<List>? l2 = null;
  List<Map<List, List>>? l3 = null;
  double? d = null;
  A? a = null;
  I? j = null;
  Function? f = null;
  t1? v1 = null;
  t2? v2 = null;
  t3? v3 = null;
}