Redundant SAM-constructor can't be remove for Kotlin declared function, but works on Java declared function

Why would you use SAM in kotlin? while it has native support for functions.

The SAM convention is used in java8 as a workaround not having native function support.

from kotlin doc#sam-conversions:

Note that SAM conversions only work for interfaces, not for abstract classes, even if those also have just a single abstract method.

Also, note that this feature works only for Java interop; since Kotlin has proper function types, automatic conversion of functions into implementations of Kotlin interfaces is unnecessary and therefore unsupported.

you should then declare a function directly.

fun setPositiveButton(resId: Int, listener: (DialogInterface, Int) -> Unit) {
    listener.invoke(
            //DialogInterface, Int
    )
}

and then it can be used

setPositiveButton(1, { _, _ -> doStuff() })

---

In kotlin 1.4 you can use SAM conversions for Kotlin classes.

fun interface Listener {
    fun listen()
}

fun addListener(listener: Listener) = a.listen()

fun main() {
    addListener {
        println("Hello!")
    }
}

Extending @humazed answer as compiler complains that

lambda argument should be moved out of parenthesis

setPositiveButton("ok"){_,_ -> doSomething()}