Unresolved reference after changing lambda to method reference-CodePudding

In the following example (also on Kotlin Playground), IntelliJ offers to change the lambda (as in the commented-out first line of main) to a method reference (as shown in the second line of main).

fun Int.matches1(n: Int): Boolean = TODO()
fun Int.matches2(n: Int): Boolean = TODO()

fun main() {
    // val matches: Int.(Int) -> Boolean = { n -> matches1(n) }
    val matches: Int.(Int) -> Boolean = ::matches1
}

The line containing the lambda works fine. However, if I try to use the method reference, the Kotlin compiler rejects it with Unresolved reference: matches1. Why?

CodePudding user response：

You need to specify the receiver type, since you're trying to reference an extension function. It's similar to when you want to reference a function that belongs to a class. So this works:

val matches: Int.(Int) -> Boolean = Int::matches1