Kotlin: Idiomatic & Declarative way to find count of a loop without mutation

Question

How to count no.of times a loop has run with a condition, for example:

var count = 0
while (stk.isNotEmpty()) {
  stack.pop()
  count++
}

But this involves a temporary counter and mutation. Is there a better idiomatic and declarative way without using any temp variable and mutation. I could come-up with something like this, but it does feel hacky:

val count = stk.takeWhile { stk.isNotEmpty() }.also { stk.pop() }.count()

Answer 1

The Kotlin standard library does not offer what you are looking for, but you could create something you are searching for own your own:

fun repeatWhile(condition: () -> Boolean, action: () -> Unit): Int {
    var count = 0
    while (condition()) {
        action()
        count++
    }
    return count
}

And use it like this:

val stack = Stack<Int>()
stack.push(1)
stack.push(2)
stack.push(3)

val count = repeatWhile({ stack.isNotEmpty() }) {
    stack.pop()
}

println(count) // 3

Personally, I don't think this a better than exposing the while-loop and the counter variable to the call-site, like you did in your question.