| // Copyright (c) 2018, 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 We say that the parameterized type G<T1..Tk> is regular-bounded |
| /// when Tj <: [T1/X1 .. Tk/Xk]Bj for all j, 1 <= j <= k, where X1..Xk are the |
| /// formal type parameters of G in declaration order, and B1..Bk are the |
| /// corresponding upper bounds. |
| /// This means that each actual type argument satisfies the declared upper bound |
| /// for the corresponding formal type parameter. |
| /// We extend covariance for generic class types such that it can be used also in |
| /// cases where a type argument violates the corresponding bound. |
| /// For instance, assuming the classes [C] and [D] as declared in the |
| /// [Motivation] section, [C<D>] is a subtype of [C<Object>]. This is new because |
| /// [C<Object>] used to be a compile-time error, which means that no questions |
| /// could be asked about its properties. Note that this is a straightforward |
| /// application of the usual covariance rule: [C<D> <: C<Object>] because |
| /// [D <: Object]. We need this relaxation of the rules in order to be able to |
| /// define which violations of the declared bounds are admissible. |
| /// @description Checks that assigning [Object] as a bound of super-bounded type |
| /// does not cause compile error in case of several type parameters. |
| /// @author iarkh@unipro.ru |
| /// @issue #32903 |
| |
| |
| class C<X extends C<X, int>, int> {} |
| class D extends C<D, int> {} |
| |
| class E<String, X extends E<String, X, double, int>, double, int> {} |
| class F extends E<String, F, double, int> {} |
| |
| main() { |
| D d = D(); |
| C<Object?, int> c = d; |
| C<Object?, dynamic> c1 = d; |
| dynamic c2 = d; |
| |
| F f = F(); |
| E<String, Object?, double, int> e = f; |
| E<dynamic, Object?, Object, Object> e1 = f; |
| dynamic e2 = f; |
| } |