Lambda-Map Performance in Kotlin

Mon, 19 Nov 2018 00:00:00 +0000

Working on an enterprise application written in Kotlin, I’ve recently noticed something that felt “off” to me. Perhaps you’ve seen it, perhaps you’ve written it — maybe even recently! It looks something like this (I call this a Lambda-Map):

object Demo {
  fun main() {
       listOf(1,2,3,4).map {
            plusOne(it)
        }
    }

    private fun plusOne(i: Int): Int = i + 1
}

Sure, this plusOne function isn’t really necessary. We can just inline it in the Lambda, but imagine for just a moment that this function does much, much more than just add one to a number. It then feels just to have that code pulled out into a private function — but that’s not the offender here.

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Lambda-Map Performance in Kotlin