Type of a function type?

Support
1

Is there any way to get the type of a function type, e.g.

foo((() -> Unit)::class)

but that actually works?

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2

It doesn’t seem like the normal syntax for it works sadly. However, this workaround is valid for now:

inline fun <reified T: Any> clazz() = T::class 

fun main() {
    println(clazz<() -> Unit>())
}
3

() -> Unit is translated to Function0<Unit> internally so Function0::class should work. Same with Function1 for functions with 1 argument, etc.

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4

You can also use a new API for types:

typeOf<() -> Unit>() // () -> kotlin.Unit
typeOf<() -> Unit>().jvmErasure // class kotlin.Function0
typeOf<() -> Unit>().jvmErasure.java // interface kotlin.jvm.functions.Function0
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5

Is that still experimental?

6

It seems so. It’s been introduced since Kotlin 1.3.60, but it’s still marked as experimental.

7

That said, experimental is most likely save to use in this case. There are a few outstanding issues with typeof. The most problematic in my oppinion is that currently typeof<MutableList<String>() == typeof<List<String>>() evaluates to true (https://youtrack.jetbrains.com/issue/KT-35877).
For a “full” list you can check:

1 Like
8

Yes, I also noticed that when was experimenting with mutable collection interfaces.

9

Thanks everyone! Turns out we were following a bit of a misguided path tho so we didn’t actually need this? sorry >.<

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