| // 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 It’s currently a compile-time error for a class to implement, |
| /// extend or mix-in the Enum class. |
| /// |
| /// Because we want to allow interfaces and mixins that are intended to be |
| /// applied to enum declarations, and therefore to assume Enum to be a |
| /// superclass, we loosen that restriction to: |
| /// |
| /// It's a compile-time error if a non-abstract class has Enum as a |
| /// superinterface (directly or transitively) unless it is the corresponding |
| /// class of an enum declaration. |
| /// |
| /// It is a compile-time error if a class implements, extends or mixes-in the |
| /// class or interface introduced by an enum declaration. (An enum class can’t |
| /// be used as a mixin since it is not a mixin declaration and the class has a |
| /// superclass other than Object, but we include “mixes-in” for completeness.) |
| /// |
| /// It's a compile-time error if a class or mixin declaration has Enum as a |
| /// superinterface and the interface of the declarations contains an instance |
| /// member with the name values, whether declared or inherited. If any concrete |
| /// class implements this interface, it will be an enum declaration class, and |
| /// then the values member would conflict with the static values constant getter |
| /// that is automatically added to enum declaration classes. Such an instance |
| /// values declaration is either useless or wrong, so we disallow it entirely. |
| /// |
| /// It's a compile-time error if a class, mixin or enum declaration has Enum as |
| /// a superinterface, and it declares a non-abstract instance member named index. |
| /// That member would override the index getter inherited from Enum, and we |
| /// currently do not allow that. |
| /// |
| /// Those restrictions allows abstract classes (interfaces) which implements |
| /// Enum in order to have the int index; getter member available, and it allows |
| /// mixin declarations to use Enum as an on type because mixin declarations |
| /// cannot be instantiated directly. |
| /// |
| /// The restrictions still ensure enum values are the only object instances |
| /// which implements Enum, while making it valid to declare abstract class |
| /// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and |
| /// mixins intended to be used in declaring enum classes. It's also impossible |
| /// to override or prevent the instance index and static values members without |
| /// causing a compile-time error. Say implementing an interface with |
| /// `Never get index;` as a member, then because it's not possible to override |
| /// `int get index;` from Enum, the resulting class does not implement its |
| /// interface and is a compile-time error. |
| /// |
| /// @description Check that it is a compile-time error if a class extends |
| /// a class declared by an enum declaration. |
| /// @author sgrekhov@unipro.ru |
| |
| // SharedOptions=--enable-experiment=enhanced-enums |
| |
| enum E { |
| e1, |
| e2 |
| } |
| |
| abstract class E1 extends E { |
| // ^ |
| // [analyzer] unspecified |
| // [cfe] unspecified |
| } |
| |
| class E2 extends E { |
| // ^ |
| // [analyzer] unspecified |
| // [cfe] unspecified |
| } |
| |
| main() { |
| E1? e1; |
| E2? e2; |
| } |