vararg parameter in a Kotlin lambda

I'd like to define a function `f()` as follows (just an example) :

val f: (vararg strings: String) -> Unit = { for (str in it) println(str) }

so that I could invoke it with `f("a","b","c")`. For the above definition of `f()` I get the compilation error, pointing at the `vararg` modifier (Kotlin v. 1.3.60 ) :

Unsupported [modifier on parameter in function type]

How can I define a lambda that accepts a `vararg` parameter ?

I'm afraid this is not possible. The following demonstrates the type of a function with `vararg`. A `vararg` parameter is represented by an `Array`:

fun withVarargs(vararg x: String) = Unit

val f: KFunction1<Array<out String>, Unit> = ::withVarargs

This behavior is also suggested in the [docs][1]:
> Inside a function a vararg-parameter of type `T` is visible as an array of `T`, i.e. the ts variable in the example above has type `Array<out T>`.

So you had to use an `Array<String>` in your example. Instead of writing your function as a lambda, you may use an ordinary function that allows to use `vararg` and make the call look as desired:

fun f(vararg strings: String) = strings.forEach(::println)

f("a","b","c")


[1]:

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If you need a function pointer (to be passed as an argument). It can be achieved with a workaround (hack):

fun f(vararg strings: String): Unit = strings.forEach(::println)


val fWrapper:(Array<String>)-> Unit = {arr:Array<String>->f(*arr)}

Since vararg is not possible to be defined in functions signatures I'll go for this:

val f: (ArrayList<String>) -> Unit = { for (str in it) println(str) }

```
inline infix <reified T, R : Any> fun foo(funcs: (vararg arg: T) -> R) = this.bar(funcs)
```