is there any way to create an empty array of a gen...

# announcements

[tschuchort]

is there any way to create an empty array of a generic type?

[Andreas Sinz]

Generic type unknown at compile-time?

[Shawn]

you may have to reify your generic type and inline the function in question

[Shawn]

inline fun <reified T> emptyGenericArray(): Array<T> {
  return arrayOf()
}

[bloder]

maybe this?

inline fun <reified T> genericArrayOf() : Array<T> = arrayOf()

[bloder]

oh sorry LOL

[tschuchort]

not possible. The method is a class method so it can not be reified. Basically I have to implement an interface of the sort fun <A : Something> foo(bar: Class<A>): Array<A>

[Allan Wang]

If the empty array is an immutable placeholder, you can look at the empty array implementation in kotlin:

https://github.com/JetBrains/kotlin/blob/1.2.60/core/builtins/src/kotlin/ArrayIntrinsics.kt#L24

You can sort of cast an empty array for any type

[kristofdho]

that's what i said & deleted, since the exact same problem occurs at the arrayOfNulls<T>(0) call, T is again not reified

[tschuchort]

It's probably not supposed to be immutable. "The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers." Tbh I have no idea how anyone is supposed to implement this

[tschuchort]

god I hate the JVM

[kristofdho]

if it's empty, there is nothing to modify, it'll always be immutable

[tschuchort]

there's fun <T> Array<T>.plus(element: T): Array<T> though and if I return an arrayOfNulls<Any?>(0) as Array<T> than calling that method on it will fail

[kristofdho]

the plus function already contains the type in this (being an Array<T>), if you're confused as to why it's not reified

[tschuchort]

I'm just saying there is no way I can create an empty Array<T> for any T

[tschuchort]

even arrayOfNulls<Any?>(0) as Array<SomeClass?> already doesn't work 😕

[kristofdho]

i'm trying but i cant even find something hacky. deeper issue is the bad method signature, because like you say, you can't just magically pull a typed array out of your ass

[bloder]

Well, it would be good if you could use list instead of array

fun <T : Any> genericListOf() : List<T> = arrayOf<KClass<T>>().mapNotNull { it.objectInstance }

Do you know any solution like that to arrays?

[kristofdho]

i do not recomend using it, but i found this

override fun <T : Something> foo(bar: Class<T>): Array<T>
    = java.lang.reflect.Array.newInstance(bar, 0) as Array<T>

[diesieben07]

java.lang.reflect.Array.newInstance is the way to go if you need this. It's ugly but perfectly fine to use.

[tschuchort]

Thx that looks like it might work. The method probably isn't gonna be called often so reflection shouldn't be a problem

[diesieben07]

It's a JVM intrinsic, it's not much slower than just creating a new array the "normal way".