Is there a reason `kotlin.Array<E>` doesn't ...

# stdlib

[Rob Elliot]

Is there a reason kotlin.Array<E> doesn't implement kotlin.collections.Iterable<E>? They both define public operator fun iterator(): Iterator<E>.

I know Java arrays don't, but does that limit Kotlin ones?

(I've often thought it would be convenient if Array<E> : FixedLengthMutableList<E> & FixedLengthMutableList<E> : List<E>, if that could all be done synthetically at compile time - is it reflection that prevents this? If so another reason to loathe reflection...)

[Rob Elliot]

I note Scala doesn't do anything like this either, and they're generally more brutal about favouring types over compatibility, so I guess there are fundamental reasons for not making Array implement a collections interface. Be interested to know what they are.

[dmitriy.novozhilov]

On JVM kotlin.Array<E> is replaced by javas E[], which can not be somehow modified by Kotlin, so Kotlin inherit all contracts and limitations for arrays from Java

[Rob Elliot]

Yes, I was wondering if something synthetic could be done at compile time, but I guess to maintain interoperability with Java if you allowed an Array to be typed as an Iterable you'd have to do a runtime check every time you passed an Iterable to a non-Kotlin method in case it were an Array, in which case it would need to be boxed using Arrays.listOf.

[dmitriy.novozhilov]

But why do you need this? It won't bring much value but may lead to a lot of implicit overhead when array will be converted to list

Basically, arrays are needed for two things:
1. Reading raw input (ByteArray and IO)
2. Low-level implementation for actual collections
For everything else, there's Mastercard array.toList()

[Rob Elliot]

I don't need it, it's just a (very) mild itch, so I was curious what the reason was - I mean, you don't "need" a common supertype of Set & List, you could just use toSet and toList whenever you need to convert between them, but when all you want to do is iterate over them it's nice not to have to do that. There are loads of Java APIs that are still array based.