Hi, does someone knows how to defined a function o...

# getting-started

[xun su]

Hi, does someone knows how to defined a function of any type in kotlin ? no matter what the param and return are . In typescript, we can do it like this:

type Fn = (...args:any[]) -> any

but I don't know how to do it in Kotlin.

[Joffrey]

In Kotlin, Any? is the supertype of all types, so you could use that for arguments and the return value. If you also want a variable number of arguments, you can use `vararg`:

fun takeAnything(vararg args: Any?): Any?

[xun su]

but how to defined a type like this ? say I wanna define a map with key of type string, and the value is a funciton. ie :

val something  = mapOf<String,???>("+" to ::plus, "-" to :: sub)

what should I put here instead of ??? it is a function

[hfhbd]

mapOf<String, Function<*>>

[Ruckus]

Can't try it right now, but maybe Function<*> https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-function.html

[Ruckus]

@hfhbd Beat me to it 😀

[xun su]

oops, seems not work,

[xun su]

image.png

[Joffrey]

You're putting the <...> in the wrong place, they should be between mapOf and the opening parenthesis

[xun su]

yes you are right

[xun su]

my bad

[xun su]

I just find it

[xun su]

😅

[hfhbd]

But if you only need to store operators, you could find the common function signature and use it as parameter, for example mapOF<String, (Int, Int) -> Int> for integers of course

[xun su]

Yes, it is a demo here, I'm learning kotlin maybe someday will encounter more complicate situation, thanks. but one more question, how to learn Kotlin types? I mean in TS there is project named TypeChallenge on github (https://github.com/type-challenges/type-challenges). we can do some exercise to learn about types in TS.