Hi all! I have a KMP with a react website and an Android application. To support the functional components, I make my props (RProps) external interfaces in the common module. However, when I try to build the Android application, it complains about these external interfaces:

Modifier 'external' is not applicable to 'class'

It looks (for example) like this:

external interface EventDetailsContractProps: BaseProps {
    var eventId: UUID
    var handler: EventDetailsContract.Handler
}

interface EventDetailsContract {
    interface Handler: EventSummaryContract.Handler {
        fun onEventDetailsFinished()
    }
}

data class EventDetailsProps constructor(
    override var eventId: UUID,
    override var handler: EventDetailsContract.Handler
): EventDetailsContractProps

This code is shared between my javascript and android targets. Is there any way to resolve this? I could try:

expect interface EventDetailsContractProps {
    var eventId: UUID
    var handler: EventDetailsContract.Handler
}

And then make a platform specific

actual

Interface, but that would mean a lot of boilerplate (As I would have to rewrite the interface 3 times).

You can’t use

external

in outside of Kotlin/JS. Also not with

expect

/

actual

. You’ll have to wrap your props.

external interface MyProps<T> {
   var value: T
}

Then your component has

MyProps<EventDetailsContractProps>

as props where

EventDetailsContractProps

is a regular

class

or

interface

.

kotlin-react

is annoying in that regard. For that reason and others I’ve created my own 🙂 https://github.com/fluidsonic/fluid-react (no class components though and requires IR compiler)

I think I can still write: actual external interface EventDetailsContractProps: BaseProps

If that would be possible then common code is broken because things like

value is EventDetailsContractProps

or

value.equals(…)

etc. won’t work and just crash.

well to support the external interfaces I already took away all reified things and comparisons

Yeah I didn’t want to make all the compromises like that or losing type safety b/c of

external

. Hence I’ve made my own library 😉