Kotlin: how to pass a function as parameter to another?

Question

Given function foo :

fun foo(m: String, bar: (m: String) -> Unit) {
    bar(m)
}

We can do:

foo("a message", { println("this is a message: $it") } )
//or 
foo("a message")  { println("this is a message: $it") }

Now, lets say we have the following function:

fun buz(m: String) {
   println("another message: $m")
}

Is there a way I can pass "buz" as a parameter to "foo" ? Something like:

foo("a message", buz)

Answer 1

Use :: to signify a function reference, and then:

fun foo(msg: String, bar: (input: String) -> Unit) {
    bar(msg)
}

// my function to pass into the other
fun buz(input: String) {
    println("another message: $input")
}

// someone passing buz into foo
fun something() {
    foo("hi", ::buz)
}

Since Kotlin 1.1 you can now use functions that are class members ("Bound Callable References"), by prefixing the function reference operator with the instance:

foo("hi", OtherClass()::buz)

foo("hi", thatOtherThing::buz)

foo("hi", this::buz)