there's a method which takes a @FunctionalInterfac...

# announcements

[Gyuhyeon]

there's a method which takes a @FunctionalInterface as a parameter. I can see that passing a lambda like

.filter{req: ClientRequest, next: ExchangeFunction ->
    // do something
}

works.

However, what I'd like to do is pass a function reference instead of the lambda so that I don't have to actually put 50 lines of code inside the .filter call.

I'm quite new to Kotlin and I have a very fragile understanding of higher order functions, so I have no idea how to achieve this.
I thought making the method like this -

private fun customFilter(request: ClientRequest, next: ExchangeFunction){

}

and calling like .filter(::customFilter) would work, but it didn't - IDE tells me

Type mismatch.
Required:
ExchangeFilterFunction
Found:
KFunction2<@ParameterName ClientRequest, @ParameterName ExchangeFunction, Unit>

It seems like I have to somehow implement the ExchangeFilterFunction.java which is a java @FunctionalInterface ...? Any advice is appreciated

[Gabriel Shanahan]

The customFilter method is defined on the ClientRequest class (https://kotlinlang.org/docs/tutorials/kotlin-for-py/member-references-and-reflection.html), so the method reference is bound to an instance of that class. I think this should work

val x = ClientRequest(...)
.filter(x::customFilter)

[Gabriel Shanahan]

if there is no need for customFilter to access the instance, put it in the companion object, then you should be able to do ClientRequest::customFilter. I don't have time to try it out though, so I'm not a 100% sure about this