blob: 8e7692a808851879816c5d071e094000a54e6d3b [file] [log] [blame]
* 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 [void] as a bound of super-bounded type
* does not cause compile error in case of several type parameters.
* @author
* @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 = new D();
C<void, int> c = d;
C<void, void> c1 = d;
dynamic c2 = d;
F f = new F();
E<String, void, double, int> e = f;
E<void, void, void, void> e1 = f;
dynamic e2 = f;