Do Fun Interfaces work with extension functions? `...

# announcements

[Björn Mayer]

Do Fun Interfaces work with extension functions?

fun interface PropHandler<P> {
    fun P.handle(): Unit
}

[kralli]

Yes.

fun interface PropHandler<P> {
    fun P.handle()
}

fun <P> a(handler: PropHandler<P>) {}

fun main() {
    a<String> { }
}

[Björn Mayer]

and how do I invoke handle on a String?

fun <P> a(handler: PropHandler<P>) {
    // invoke handler on object of type P
}

[kralli]

Ah, now I understand your problem. You will need an auxiliary function like so:

fun a(handler: PropHandler<String>) {
    val string = "Hello World"
    
    handler.invoke(string)
}

private fun <P> PropHandler<P>.invoke(value: P){
    value.handle()
}

[Arkadii Ivanov]

with(handler) {
obj_of_type_p.handle()
}

[Björn Mayer]

Arkadii’s solution did it.
Thank you both very much 🙂

[kralli]

Right, I forgot to mention with. Thanks Arkadii for pointing that one out. If you want to know a bit more about the why, you can take a look at this thread https://kotlinlang.slack.com/archives/C0922A726/p1604502966429600?thread_ts=1604498090.426500&cid=C0922A726.