Fold list to pair with destructuring assignment in kotlin

Question

I try to get multiple results from a folding operation on a list of characters and use a destructuring assignment to both values to their own variables afterwards. But this seems to result in an exception by the kotlin compiler:

java.lang.UnsupportedOperationException: Don't know how to generate outer expression for class <closure-Test$1>

Strangely (to me) without the destructuring, this works as intended. Here is an example:

val fstSec = "fst"

val (fst, snd) = "this is a test for folding to pair"
    .toCharArray()
    .fold(Pair(0, 0), { sumPair, char ->
        when (fstSec) {
            "fst" -> Pair(sumPair.first + char.toInt()*2, sumPair.second + char.toInt())
            "snd" -> Pair(sumPair.first + char.toInt(), sumPair.second + char.toInt()*2)
            else -> throw RuntimeException("exception")
        }
    })

println("( $fst , $snd )")

This results in the exception.

val fstSec = "fst"

val pair = "this is a test for folding to pair"
    .toCharArray()
    .fold(Pair(0, 0), { sumPair, char ->
        when (fstSec) {
            "fst" -> Pair(sumPair.first + char.toInt()*2, sumPair.second + char.toInt())
            "snd" -> Pair(sumPair.first + char.toInt(), sumPair.second + char.toInt()*2)
            else -> throw RuntimeException("exception")
        }
    })

println("( ${pair.first} , ${pair.second} )")

This one works as expected, and the only thing I removed was the destructuring. Strangely, if I remove the inner when (and replace it by a Pair constructor only), the code works both times.

Thanks in advance.

Answer 1

This is a bug in Kotlin Script compilation.

Thanks @razr for reporting it: KT-22029