Which do you prefer? :one: `for (index in 0 until...

# codingconventions

[Mark]

Which do you prefer?

1️⃣ for (index in 0 until itemCount) {

2️⃣ repeat(itemCount) { index ->

[asdf asdf]

I’d say it depends on the use case, if the index represents something like a position I would use 1, but if it’s only used as the current iteration of the loop I would use 2

[Joffrey]

Yes, I'd say it depends on what you want to express. Use repeat if you want to repeat something multiple times. Use forEach or forEachIndexed if you want to iterate a collection. I rarely ever use explicit for loops

[Mark]

I should probably have mentioned that, here, an index refers to an item index in a list (but we do not have direct access to that list, otherwise we would just use forEachIndexed )

[Joffrey]

Could you please share a bit more about how you use that loop, then?

[Mark]

Any API that accepts a position (in a list) as a function arg. For example, getItemId in RecyclerView.Adapter In my particular case (not using that exact function) I have:

for (position in 0 until itemCount) {
    val item = itemAtPosition(position)
    if (item is Foo) {
        notifyItemChanged(position)
    }
}

[ephemient]

if it's over a list, I would definitely write

for (index in list.indices) {

[ephemient]

(unless for ((index, elem) in list.withIndex()) { works better in context, of course)

[Mark]

Ok, but in this case there is no direct access to the list

[Jan]

Kind of related: turns out collection operators create a lot of garbage (gc) if used often, e.g. in render loops like jetpack compose where regular for loops will not.

Most of the time you'd want to prioritize readability though.

[ephemient]

compose has internal helpers that avoid allocating, https://github.com/androidx/androidx/blob/androidx-main/compose/ui/ui-util/src/commonMain/kotlin/androidx/compose/ui/util/ListUtils.kt

[ephemient]

they only make sense on RandomAccess lists which aren't being mutated, which should be most lists, but it's hard to guarantee unless you are in control of the data (and Compose only uses those helpers on its own data)

[Jan]

Exactly

[Marcin Wisniowski]

Also if you need to use continue in your loop body, you can't use repeat.