Language/Types/Interface_Types/subtype_t50.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 a function type t1 is not assignable to a function
/// type t2 only if t1 <: t2
/// @author sgrekhov@unipro.ru


class A {}
class A1 {}
class A2 {}
class B implements A, A1, A2 {}
class C implements B {}
class D implements C {}

typedef B func(Object o);
typedef A f1(int i, D d, Map<int, num> m, var x,
             [var ox, D od, List<num> ol, bool obool]);

B f01(int i, B b, Map<int, num> m, var x,
      [var ox, B? ob, List<num>? ol, bool? obool]) => new B();

C f11(num i, A b, Map<Object, Object> m, var x) => new C();

main() {
  f1 fvar = f11;
//          ^
// [analyzer] unspecified
// [cfe] unspecified
}