Is there any way to pass a `Collection<I>` (not re...

# getting-started

[dave08]

Is there any way to pass a Collection<I> (not reified) with a spread operator to a vararg function? It seems like toTypedArray() won't work without reified...

[Youssef Shoaib [MOD]]

Does your vararg function accept a non-reified generic or Any?? if so, I think you can simply upcast your Collection to Collection<Any?> and then do toTypedArray()

[dave08]

It's a non-reified generic, I'm trying to use Lettuce's (Java) RedisFuture<Long> del(K... keys);

[dave08]

And I need to implement override suspend fun expire(ids: Collection<I>)

[dave08]

(I == K)

[Youssef Shoaib [MOD]]

I think just typing it as Any? should work then

[phldavies]

fun <T> del(vararg values: T) {
    values.forEach { 
        println("deleting: $it")
    }
}

fun <T> expire(ids: Collection<T>) {
    del(*ids.toTypedArray<Any?>())
}

fun main() {
    expire(listOf("hello", "world"))
}

[dave08]

Type mismatch.
Required:
I!
Found:
Array<Any?>

[phldavies]

yeah - I just realised your K is bound by the Lettuce interface and cannot be lifted to Any?.

[dave08]

It's a real pity they don't even have an overload taking in a collection...

[dave08]

I do need to pass the KClasses or something into my class for Kotlinx serialization though, does that help?

[dave08]

And for the key and for the value

[phldavies]

an option would be to take the potentially unsafe cast and use *(ids.toTypedArray<Any?>() as Array<I>) assuming you can ensure that I == K

[phldavies]

you know that ids.toTypedArray<Any?>() will only contain `I`s - so you can safely cast it.

[dave08]

I guess that's assured by my function signature, no?

override suspend fun expire(ids: Collection<I>) {
        connection.async().del(*(ids.toTypedArray<Any?>() as Array<I>)).await()
    }

[phldavies]

yup, assuming async() returns an instance of the interface such that the K type-arg is your I from that context then the del call is fine (the array casting is fine by way of your signature)

[dave08]

val connection: StatefulRedisConnection<I, V> =
        redis.connect(JsonCodec(Json, keySerializer, valueSerializer))

[dave08]

Thanks!

[Ruckus]

Looks like there's an open issue for it, but it's on hold till collection literals are done: https://youtrack.jetbrains.com/issue/KT-12663/Spread-operator-for-Iterable-Collection-in-varargs