Hey guys, regaring inline classes: ```value class CoolZeroCostSequence(val arr: IntArray) { ...}``` ...

# compiler

[groostav]

Hey guys, regaring inline classes:

value class CoolZeroCostSequence(val arr: IntArray) { ...}

if i wanted to write

val seq: CoolZeroCostSequence = makeArraySequenceThing()

for(int in seq){

}

and I wanted to avoid any boxing, which is to say, I do not want to create an instance of Iterator<Int> because that would box up my elements, how can I do it?

[groostav]

in my particular case I'm also wrapping the int:

value class TraversalSequence(val array: IntArray){
  // want similar behaviour to Array<NodeEncounter> but actually IntArray
}
value class NodeEncounter(val idx: Int){
  val isLeave: Boolean get() = idx < 0
  val index: Int get() = idx.let { if(it > 0) it else -1*it }
}

[groostav]

from what I remember for needs an operator fun iterator(): Iterator<Int> , but that requres boxing... can i give you back an object with an operator fun next() on it instead?

[franztesca]

You cannot avoid boxing when using generics AFAIK. So either you go the IntArray way (aka defining a separate class for each primitive, without inheriting from generics), or you go the list way (accept boxing).
Wondering whether a compiler plugin could do this optimization behind the scenes...

[Youssef Shoaib [MOD]]

There's a really easy way to do it with a custom Iterator implementation. Iterators in Kotlin don't have to implement Iterator interface, they only need to have operator fun next() and operator fun hasNext(): Boolean. So what you can do is something like this:

class IntIterator(private val arr: IntArray, private var index: Int = 0) {
  operator fun next(): Int = arr[index++]
  operator fun hasNext(): Boolean = index < arr.length
}
operator fun CoolZeroCostSequence.iterator(): IntIterator = IntIterator(arr)

[ephemient]

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-int-iterator/ already exists

[groostav]

does this type properly avoid boxing in a for(elem in somethingThatsIntIterator)?

[Youssef Shoaib [MOD]]

The pre-existing Int iterator implements the Iterator interface, so I wasn't quite sure if it would be boxing or not, hence why I made my own. You can experiment with returning the pre-existing one and seeing what code is generated. I'm 100% sure that a custom one will not box, though.

[ephemient]

it boxes if used generically but contains unboxed overloads that Kotlin can use: https://github.com/jetbrains/kotlin/pull/4753