kotlin-stdlib / kotlin.collections / reduceRightIndexedOrNull

reduceRightIndexedOrNull

Common
JVM
JS
Native
1.4
inline fun <S, T : S> Array<out T>.reduceRightIndexedOrNull(
    operation: (index: Int, T, acc: S) -> S
): S?
(source)
inline fun ByteArray.reduceRightIndexedOrNull(
    operation: (index: Int, Byte, acc: Byte) -> Byte
): Byte?
(source)
inline fun ShortArray.reduceRightIndexedOrNull(
    operation: (index: Int, Short, acc: Short) -> Short
): Short?
(source)
inline fun IntArray.reduceRightIndexedOrNull(
    operation: (index: Int, Int, acc: Int) -> Int
): Int?
(source)
inline fun LongArray.reduceRightIndexedOrNull(
    operation: (index: Int, Long, acc: Long) -> Long
): Long?
(source)
inline fun FloatArray.reduceRightIndexedOrNull(
    operation: (index: Int, Float, acc: Float) -> Float
): Float?
(source)
inline fun DoubleArray.reduceRightIndexedOrNull(
    operation: (index: Int, Double, acc: Double) -> Double
): Double?
(source)
inline fun BooleanArray.reduceRightIndexedOrNull(
    operation: (index: Int, Boolean, acc: Boolean) -> Boolean
): Boolean?
(source)
inline fun CharArray.reduceRightIndexedOrNull(
    operation: (index: Int, Char, acc: Char) -> Char
): Char?
(source)
@ExperimentalUnsignedTypes inline fun UIntArray.reduceRightIndexedOrNull(
    operation: (index: Int, UInt, acc: UInt) -> UInt
): UInt?
(source)
@ExperimentalUnsignedTypes inline fun ULongArray.reduceRightIndexedOrNull(
    operation: (index: Int, ULong, acc: ULong) -> ULong
): ULong?
(source)
@ExperimentalUnsignedTypes inline fun UByteArray.reduceRightIndexedOrNull(
    operation: (index: Int, UByte, acc: UByte) -> UByte
): UByte?
(source)
@ExperimentalUnsignedTypes inline fun UShortArray.reduceRightIndexedOrNull(
    operation: (index: Int, UShort, acc: UShort) -> UShort
): UShort?
(source)

Accumulates value starting with the last element and applying operation from right to left to each element with its index in the original array and current accumulator value.

Returns null if the array is empty.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduceRightOrNull { string, acc -> acc + string }) // dcba
println(strings.reduceRightIndexedOrNull { index, string, acc -> acc + string + index }) // dc2b1a0

println(emptyList<String>().reduceRightOrNull { _, _ -> "" }) // null
//sampleEnd
}

Parameters

operation - function that takes the index of an element, the element itself and current accumulator value, and calculates the next accumulator value.

Common
JVM
JS
Native
1.4
inline fun <S, T : S> List<T>.reduceRightIndexedOrNull(
    operation: (index: Int, T, acc: S) -> S
): S?
(source)

Accumulates value starting with the last element and applying operation from right to left to each element with its index in the original list and current accumulator value.

Returns null if the list is empty.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduceRightOrNull { string, acc -> acc + string }) // dcba
println(strings.reduceRightIndexedOrNull { index, string, acc -> acc + string + index }) // dc2b1a0

println(emptyList<String>().reduceRightOrNull { _, _ -> "" }) // null
//sampleEnd
}

Parameters

operation - function that takes the index of an element, the element itself and current accumulator value, and calculates the next accumulator value.