reduceOrNull

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

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

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

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

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

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

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

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

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

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

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

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

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

Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element.

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.reduceOrNull { acc, string -> acc + string }) // abcd
println(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }) // ab1c2d3

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

Parameters

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

inline fun <S, T : S> Iterable<T>.reduceOrNull(
    operation: (acc: S, T) -> S
): S?

Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element.

Returns null if the collection is empty.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduceOrNull { acc, string -> acc + string }) // abcd
println(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }) // ab1c2d3

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

Parameters

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