kotlin-stdlib/kotlin.collections/reduceRightOrNull

reduceRightOrNull

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

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.

Since Kotlin

1.4

Samples



import kotlin.test.*
fun main() { 
   //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?(source)

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.

Since Kotlin

1.4

Samples



import kotlin.test.*
fun main() { 
   //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.