Hey is it possible to make an abstract enum Or a type that i

Question

Hey is it possible to make an abstract enum Or a type that is equal to Enum lt T gt with added methods

Joffrey · Answer

Enums can have any method you want they are regular classes apart from the fact that they have a fixed known set of instances However they can t ~be abstract~ allow subclasses by definition because it would indirectly allow more instances

Joffrey · Answer

You can for instance write ```enums class MyEnum VALUE1 VALUE2 fun myFun Int = 42 ```

Rob Elliot · Answer

They re kind of always abstract ```enum class Foo Foo1 override fun something = 1 Foo2 override fun something = 2 abstract fun something Int ```

Joffrey · Answer

Right maybe my initial comment is misleading in this respect I meant they can t be abstract or open in the sense that you can t create subclasses of them

Rob Elliot · Answer

Oh agreed sorry wasn t trying to be snide just wanted the OP to know it was possible to have abstract members

Joffrey · Answer

No worries I didn t take it that way slightly smiling face It s actually really worth pointing that out because maybe the OP is interested in providing different implementations for different enum values So thanks

Ayfri · Answer

Thanks but it s not exactly what I meant I need an interface or an abstract class to extend `Enum lt gt ` then I need multiple Enum classes to implement this interface And I need this type for multiple methods where I have a selector of selectors drop downs for an UI app

Joffrey · Answer

I m not sure I understand your use case well In particular why can t you use a regular interface and make your enum classes implement that interface In other words why is it important that the interface itself needs to be a subtype of `Enum` which btw is not possible

Joffrey · Answer

By the way I believe you should be able to define a method that only accept enums that implement a particular interface ```fun lt T gt myFun value T Unit where T Enum lt T gt T MyInterface value is both an Enum and a MyInterface ``` Can t double check the code I m on mobile right now See the doc there <https kotlinlang org docs generics html upper bounds|https kotlinlang org docs generics html upper bounds>

Rob Elliot · Answer

It does work There s not a lot on `Enum` that s useful just `name` and `ordinal` but if you make the type reified you can get the set of values which might be useful ```inline fun lt reified T gt myFun value T where T Enum lt T gt T MyInterface println enumValues lt T gt toSet ```

Rob Elliot · Answer

Which in combo allows you to have generic interfaces cool Thanks Joffrey opened up a new technique to think about in future ```interface Wrapper lt T gt val foo T enum class IntWrapper Wrapper lt Int gt E1 override val foo = 1 E2 override val foo = 1 inline fun lt reified A B gt myFun value A where A Enum lt A gt A Wrapper lt B gt value is a Wrapper lt B gt val b B = value foo and it s an Enum println value name println value ordinal and you can get the values of that enum println enumValues lt A gt ```

Ayfri · Answer

And what if my function needs to return the values of the Enum

Rob Elliot · Answer

Return them

Rob Elliot · Answer

```inline fun lt reified A B gt myFun value A List lt A gt where A Enum lt A gt A Wrapper lt B gt return enumValues lt A gt toList ```

Ayfri · Answer

Yeah okay it was simple I was just tired thanks for the help everyone

Matteo Mirk · Answer

If you need to define a hierarchy of finite set of types maybe you should use sealed interfaces or classes Although having enums implement the same interface could suffice for your case as shown above