inline fun <S, T : S> Array<out T>.reduceRightOrNull(
    operation: (T, acc: S) -> S
): S?

inline fun ByteArray.reduceRightOrNull(
    operation: (Byte, acc: Byte) -> Byte
): Byte?

inline fun ShortArray.reduceRightOrNull(
    operation: (Short, acc: Short) -> Short
): Short?

inline fun IntArray.reduceRightOrNull(
    operation: (Int, acc: Int) -> Int
): Int?

inline fun LongArray.reduceRightOrNull(
    operation: (Long, acc: Long) -> Long
): Long?

inline fun FloatArray.reduceRightOrNull(
    operation: (Float, acc: Float) -> Float
): Float?

inline fun DoubleArray.reduceRightOrNull(
    operation: (Double, acc: Double) -> Double
): Double?

inline fun BooleanArray.reduceRightOrNull(
    operation: (Boolean, acc: Boolean) -> Boolean
): Boolean?

inline fun CharArray.reduceRightOrNull(
    operation: (Char, acc: Char) -> Char
): Char?

@ExperimentalUnsignedTypes inline fun UIntArray.reduceRightOrNull(
    operation: (UInt, acc: UInt) -> UInt
): UInt?

@ExperimentalUnsignedTypes inline fun ULongArray.reduceRightOrNull(
    operation: (ULong, acc: ULong) -> ULong
): ULong?

@ExperimentalUnsignedTypes inline fun UByteArray.reduceRightOrNull(
    operation: (UByte, acc: UByte) -> UByte
): UByte?

@ExperimentalUnsignedTypes inline fun UShortArray.reduceRightOrNull(
    operation: (UShort, acc: UShort) -> UShort
): UShort?

Accumulates value starting with the last element and applying operation from right to left to each element 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 an element and current accumulator value, and calculates the next accumulator value.

inline fun <S, T : S> List<T>.reduceRightOrNull(
    operation: (T, acc: S) -> S
): S?

Accumulates value starting with the last element and applying operation from right to left to each element 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 an element and current accumulator value, and calculates the next accumulator value.