Is there a way to declare this Swift enum using se...

# getting-started

[nestserau]

Is there a way to declare this Swift enum using sealed classes in Kotlin?

enum Optional<T> {
    case None
    case Some(T)
}

[diesieben07]

sealed class Optional<out T> {
    object None : Optional<Nothing>()
    data class Some(val value: T) : Optional<T>()
}

[nestserau]

Thank you very much! I guess Some should be declared as data class Some<out T>(val value: T): Optional<T>(), otherwise it doesn’t compile?

[Olivier]

val object : MyClass? = ...

[nestserau]

Olivier, my real-world enum looks like this now:

sealed class MessageResult<out T> {
    data class ok<out T>(val value: T): MessageResult<T>()
    data class failed(val error: MessageError): MessageResult<Nothing>()
}

So it’s a little bit more complex than an optional. 🙂

[nestserau]

I didn’t know about Nothing, but now I do, so the task is solved.

[diesieben07]

I guess Some should be declared as data class Some<out T>(val value: T): Optional<T>(), otherwise it doesn’t compile?

Yes, of course. Missed that, sorry.

[Olivier]

@nestserau Arrow has a Etiher class that can fit you needs
https://github.com/arrow-kt/arrow/blob/master/modules/core/arrow-core/src/main/kotlin/arrow/core/Either.kt

[nfrankel]

optional and either are different imho

[bjartek]

arrow has option https://arrow-kt.io/docs/arrow/core/option/

[Olivier]

Actually Aleks needs Either, he have 2 possibilities : https://kotlinlang.slack.com/archives/C0B8MA7FA/p1544438340138100?thread_ts=1544437520.137300&cid=C0B8MA7FA
- ok with a value
- error with a message

This is what Either is for.

[Narayan Iyer]

Incidentally, I was reading this article by @raulraja, which is in Scala, but the same functionalities are provided by Arrow. Differentiates when to use Either or Try or Option etc. https://www.47deg.com/presentations/2017/02/18/Functional-error-handling/