I got a switch in Swift on a Kotlin enum defined i...

# multiplatform

[Stefan Oltmann]

I got a switch in Swift on a Kotlin enum defined in commonMain and XCode complains that it's not exhaustive - but I covered every case. Is this a known bug in Kotlin/Native ?

[Sam]

Kotlin enums don’t map directly to Swift or ObjC enums so it probably wants you to add a default case. You can just put a break under it and it'll work.

[Stefan Oltmann]

Yes, I needed to add that. But what case is Swift internally missing?

[louiscad]

The case where the API evolves and further enum cases are added.

[Stefan Oltmann]

Very funny, Louis...

No, seriously: I have a "case" for every enum thing and I want no "default"-case.
Default cases are bad because if I add more items in my enum I want that switch to not compile.

Which enum case is Swift internally missing so that it says my enum is not exhaustive?

[louiscad]

It was not a joke. That's Swift's way of dealing with enums, at least when they're not defined in Swift.

[russhwolf]

It's not a missing case. Swift just doesn't understand that Kotlin enums are exhaustive.

[louiscad]

You can crash for the default case, so at least, you notice it at runtime.

[Stefan Oltmann]

So Swift is actually missing Kotlins feature to see that it's exhaustive and only wanting a "else" if some case is really missing?

[Stefan Oltmann]

Because there are Swift samples that don't have a default case.

[Stefan Oltmann]

Ok, as Sam and Russel said maybe that's Kotlin/Native problem that Kotlin enums are not directly mapped to Swift enums.

[Stefan Oltmann]

I hope that will change one day.

[Stefan Oltmann]

Thank you all.

[Grégory Lureau]

You may want to track KT-49521 for direct interop with Swift, maybe it'll allow some improvements on enums too.

[Sam]

The issue is that Kotlin enums are mapped through as ObjC classes because they can have properties and behavior. That means that Swift wants you to have a case for all possible classes when using it as a switch value. If you really want to avoid a default case, you’ll have to transform it into a Swift enum. That just seems to be more trouble than it is worth because you’ll have to remember to keep two values in sync. It’s easier just to add:

default:
    fatalerror("You need to handle another enum value")

[ankushg]

I wonder if it would be possible to use something like moko-kswift to automatically generate Swift-equivalents for KMP enums to make this a bit easier...

[Benoît]

@Stefan Oltmann This is what we use https://github.com/icerockdev/moko-kswift you should give it shot, it's a bit of a pain to setup but you only need to do it once