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kotlinlang

does an index-based `for` loop over a `List`, have equivalent performance to using `subList()`?

probably depends on your list implementation, the size of the list, the number of indices you’re traversing, etc

for most lists, subList is just a view that offsets and limits the indices. there may be some indirection overhead. probably not much, measure yourself if you want to know

and for most (but not all) lists `for (x in list)` is more expensive than `for (i in list.indices) val x = list[i]` as the latter avoids going through an iterator. but most code should not bother with such microoptimizations

that sounds good enough to me, to be honest. "no copy under-the-hood" is already a strong guarantee.

also, I forgot iterators in Kotlin are not quite zero cost

as in, relatively farther away from zero cost