kotlin-stdlib/kotlin.collections/reduceOrNull

reduceOrNull

inline fun <S, T : S> Array<out T>.reduceOrNull(operation: (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.

Since Kotlin

1.4

Samples

import samples.*
import kotlin.test.*
fun main() { 
   //sampleStart 
   val strings = listOf("a", "b", "c", "d")
assertPrints(strings.reduceOrNull { acc, string -> acc + string }, "abcd")
assertPrints(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }, "ab1c2d3")

assertPrints(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: (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.

Since Kotlin

1.4

Samples

import samples.*
import kotlin.test.*
fun main() { 
   //sampleStart 
   val strings = listOf("a", "b", "c", "d")
assertPrints(strings.reduceOrNull { acc, string -> acc + string }, "abcd")
assertPrints(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }, "ab1c2d3")

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

Parameters

operation

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