I have an interface with a function that has the signature `fun <T: Any?> asArray(tClazz: Clas...

# announcements

[mantono]

I have an interface with a function that has the signature fun <T: Any?> asArray(tClazz: Class<T>): Array<T>, how ever, I have no idea how to return an Array of type T in Kotlin on a non-reified function with only the Class as argument.

[diesieben07]

On the JVM:
val array = java.lang.reflect.Array.newInstance(componentType, length)

[diesieben07]

On JS you can use val array = js("[]").unsafeCast<Array<T>> (only works if T is not a primitive type)

[Marko Mitic]

Array<T>() 😄

[diesieben07]

That does not work if T is not reified.

[wbertan]

inline fun <reified T: Any?> asArray(tClazz: Class<T>): Array<T> = arrayOf()
Cannot use as inline?

[mantono]

Thank you @diesieben07! I thought reflection might be the solution, but I could not find out how.

[mantono]

@wbertan No, it is not possible when it is part of an interface.

[wbertan]

Oh, didn’t know! 😞

[Marko Mitic]

Arrays are tricky

[mantono]

@diesieben07 I get a ClassCastExcpetion tough 🤔

[diesieben07]

Show your code

[mantono]

val array: Array<T> = java.lang.reflect.Array.newInstance(tClazz, size) as Array<T>

[mantono]

If I do not cast it, it will just be Any and I will be unable to use it for anything.

[diesieben07]

It works for me.

[diesieben07]

What did you use as tClazz?

[mantono]

Can I see your code?

[mantono]

Long.

[diesieben07]

If you use primitive types (Int, Short, etc.) you need to ensure to use Int::class.javaObjectType. otherwise you will get a LongArray, not a Array<Long> from Array.newInstance

[mantono]

Aha, I see!

[diesieben07]

You can guard against that inside your asArray method:

java.lang.reflect.Array.newInstance(cls.kotlin.javaObjectType, 10) as Array<T>

[diesieben07]

Is there a specific reason you must use an array and not a list? Then you would not need any of this crazyness 😄

[mantono]

Yeah, that's what the interface has specified, not my interface 😢 I usually know better than to trying to use generic arrays in Kotlin.

[mantono]

Now it works anyway, thanks a lot @diesieben07! I would not have figured out this one by myself.

[mantono]

Now I just need to guard for this on all primtive types.

[mantono]

I wrote an extension function for this to List. This is the final result https://gist.github.com/mantono/914d54d0c9deb01281ca0133676968a5 once again, huge thanks for the help!

[diesieben07]

You don't need that when, you can just always call javaObjectType

[diesieben07]

That means you have to guard T by any though: <T : Any>

[mantono]

That should be acceptable.

[mantono]

Really nice, thanks 😄