Is there something like Sealed Inline Class?

# announcements

[aeruhxi]

Is there something like Sealed Inline Class?

[kyleg]

I don’t think it’s possible. Sub-classes of a sealed class extend the parent class by definition, and inline classes cannot extend a class.

[aeruhxi]

Yeah, but it should be possible to make sealed class inline as well?

[aeruhxi]

I used interface for an workaround, although it doesn't give me exhaustive checking.

[kyleg]

No because inline classes have to be final, so they cannot be extended by sub-classes.

[kyleg]

What are you trying to do? You might be able to use an enum class instead depending on your goal.

[Fleshgrinder]

This wouldn't make sense because the relationship you lay out would be removed by the compiler. Remember that inline classes are compile time types not actual types. I guess you want to model some union but Kotlin doesn't have that and it also doesn't have monomorphization, which would make your request possible.

[jw]

It's not that it would be removed, it's that it would require boxing (similar to implementing an interface today).

[Fleshgrinder]

If the sealed class is not inline itself, yes, that would work.

[aeruhxi]

Oh, yeah, I just came to realization it's not possible without monomorphization or tagging.

For better context of what I am trying to do:

interface ID
inline class AID(val value: String) : ID
inline class BID(val value: String) : ID

val result = when (id) {
    is AID -> /* do something with AID */
    is BID -> /* do something with BID */
    else -> Either.Left(
       DatabaseError.Unhandled("Wrong type of ID")
    )
}

[aeruhxi]

If I understood correctly, it gets boxed if I use it like this?

[Fleshgrinder]

Yes