kotlin slice with default and negative index

slice.kt

internal fun <T> List<T>.slice(indices: Iterable<Int>, default: (index: Int) -> T): List<T> {
    val size = indices.measureSizeOrDefault(10)
    val target = ArrayList<T>(size)
    val availRange = 0..this.lastIndex
    indices.forEach {
        val pos = if (it < 0) this.size + it else it
        if (pos in availRange) {
            target.add(this[pos])
        } else {
            target.add(default.invoke(pos))
        }
    }
    return target
}

internal fun Iterable<Int>.measureSizeOrDefault(defaultValue: Int): Int =
    when (this) {
        is IntProgression -> {
            this.run {
                when {
                    step > 0 -> if (first > last) 0 else ((last - first) / step) + 1
                    step < 0 -> if (last > first) 0 else ((first - last) / step.absoluteValue) + 1
                    else -> error("step equals zero.")
                }
            }
        }
        is Collection<Int> -> this.size
        else -> defaultValue
    }

tests.kt

internal class UtilKtTest {

    @Test
    fun slice() {
        val list = listOf(0, 1, 2, 3, 4, 5, 6, 7, 8)
        assertEquals(list.slice(1..5) { 0 }, listOf(1, 2, 3, 4, 5))
        assertEquals(list.slice(0..1) { 0 }, listOf(0, 1))
        assertEquals(list.slice(1..0) { 0 }, emptyList<Int>())
        assertEquals(list.slice(1..1) { 0 }, listOf(1))
        assertEquals(list.slice(0..0) { 0 }, listOf(0))
        assertEquals(list.slice(0..20) { it }, (0..20).toList())

        assertEquals(list.slice(-5..-1) { 0 }, listOf(4, 5, 6, 7, 8))
        assertEquals(list.slice(-5..1) { 0 }, listOf(4, 5, 6, 7, 8, 0, 1))
        assertEquals(list.slice(0..5 step 2) { 0 }, listOf(0, 2, 4))
        assertEquals(list.slice(0..6 step 2) { 0 }, listOf(0, 2, 4, 6))
        assertEquals(listOf(0, 0, 0, 0, 1, 2, 3), listOf(1, 2, 3).slice(-7..-1) { 0 })

        assertEquals(list.slice(5 downTo 0) { 0 }, listOf(5, 4, 3, 2, 1, 0))
        assertEquals(list.slice(3 downTo -3) { 0 }, listOf(3, 2, 1, 0, 8, 7, 6))
        assertEquals(list.slice(3 downTo -3 step 2) { 0 }, listOf(3, 1, 8, 6))
    }

    @Test
    fun measureSizeOrDefault() {
        assertEquals(5, (1..5).measureSizeOrDefault(10))
        assertEquals(0, (1..0).measureSizeOrDefault(10))
        assertEquals(6, (0..10 step 2).measureSizeOrDefault(10))
        assertEquals(6, (10 downTo 0 step 2).measureSizeOrDefault(10))

        assertEquals(3, listOf(1, 2, 3).measureSizeOrDefault(10))
    }
}