kotlin-stdlib/kotlin.sequences/firstNotNullOfOrNull

firstNotNullOfOrNull

inline fun <T, R : Any> Sequence<T>.firstNotNullOfOrNull(transform: (T) -> R?): R?

Returns the first non-null value produced by transform function being applied to elements of this sequence in iteration order, or null if no non-null value was produced.

The operation is terminal.

Since Kotlin

1.5

Samples

import samples.*
import kotlin.test.*
fun main() { 
   //sampleStart 
   data class Rectangle(val height: Int, val width: Int) {
    val area: Int get() = height * width
}

val rectangles = listOf(
    Rectangle(3, 4),
    Rectangle(1, 8),
    Rectangle(6, 3),
    Rectangle(4, 3),
    Rectangle(5, 7)
)

val largeArea = rectangles.firstNotNullOf { it.area.takeIf { area -> area >= 15 } }
val largeAreaOrNull = rectangles.firstNotNullOfOrNull { it.area.takeIf { area -> area >= 15 } }

assertPrints(largeArea, "18")
assertPrints(largeAreaOrNull, "18")

assertFailsWith<NoSuchElementException> { val evenLargerArea = rectangles.firstNotNullOf { it.area.takeIf { area -> area >= 50 } } }
val evenLargerAreaOrNull = rectangles.firstNotNullOfOrNull { it.area.takeIf { area -> area >= 50 } }

assertPrints(evenLargerAreaOrNull, "null") 
   //sampleEnd
}