is there a more idiomatic way to write a map-with-...

# codereview

[Jonathan Ellis]

is there a more idiomatic way to write a map-with-loop like this?

val flowed = allShapes.map {
            var p = it
            for (i in 0 until STRETCH_ITERATIONS) {
                p = flow(p)
            }
            p
        }

[ephemient]

allShapes.map {
    (0 until STRETCH_ITERATIONS).fold(it) { p, _ ->
        fold(p)
    }
}

[Jonathan Ellis]

TIL about fold, thanks!

[Joffrey]

Also, when a for loop is about repeating something some number of times, it's better expressed with the repeat(n) { ... } function. So in a case where fold wouldn't be a solution to your problem, you could at least replace the loop:

val flowed = allShapes.map {
    var p = it
    repeat(STRETCH_ITERATIONS) {
        p = flow(p)
    }
    p
}

[ephemient]

"better" is arguable; you can't break early out of repeat, and the rangeTo in a for loop is intrinsified so it doesn't cost anything more than repeat

[Joffrey]

Of course if you need complex control flow like break and continue, it's not possible. But such cases would probably not be better expressed by repeat anyway - it's not about repeating something N times if you break early.

[Jonathan Ellis]

it's pretty common to write "loop until condition or a maximum of N times"

[Joffrey]

Yes, but it's not the case here. My point is, if what you need is a plain "repeat N times" (like here), repeat is very clear and meant for this. But of course repeat is for repeating, not for other stuff. That said, I have not needed a for loop in Kotlin for quite some time, there usually are clearer alternatives for most use cases.