| // Copyright (c) 2021, 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 Allow generic function types as type arguments and bounds |
| /// |
| /// The language disallows generic function types as type arguments and bounds. |
| /// |
| /// late List<T Function<T>(T)> idFunctions; // INVALID. |
| /// var callback = [foo<T>(T value) => value]; // Inferred as above, then invalid. |
| /// late S Function<S extends T Function<T>(T)>(S) f; // INVALID. |
| /// |
| /// We remove that restriction, so a type argument and a bound can be a generic |
| /// function type. |
| /// |
| /// This requires no new syntax, and in some cases only the removal of a single |
| /// check. There might be some platforms where the implementation currently |
| /// assumes that generic function types cannot occur as the value of type |
| /// variables (an proof-of-concept attempt hit an assert in the VM). Such |
| /// assumptions will need to be flushed out with tests and fixed. |
| /// |
| /// Because we already infer List<T Function<T>(T)> in the code above, this |
| /// change will not affect type inference, it will just make the inferred type |
| /// not be an error afterwards. |
| /// |
| /// We do not expect the removal of this restriction to affect the feasibility of |
| /// type inference. After all, it's already possible to have a generic function |
| /// type occurring covariantly in a type argument, like List<T Function<T>(T) |
| /// Function()>. |
| /// @description Checks statically that generic covariant function can be a type |
| /// argument and bound for List. |
| /// @author iarkh@unipro.ru |
| |
| |
| T test1<T>(T i) => i; |
| void test2<T>() {} |
| T test3<T>() => 0 as T; |
| void test4<T>(T i) {} |
| |
| main() { |
| List<void Function<T>()> l2 = <void Function<T>()>[]; |
| l2.add(test2); |
| l2.add(test3); |
| |
| l2.add(1); |
| // ^ |
| // [analyzer] unspecified |
| // [cfe] unspecified |
| |
| l2.add(test1); |
| // ^ |
| // [analyzer] unspecified |
| // [cfe] unspecified |
| |
| l2.add(test4); |
| // ^ |
| // [analyzer] unspecified |
| // [cfe] unspecified |
| } |