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.
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 } } println(largeArea) // 18 println(largeAreaOrNull) // 18 // val evenLargerArea = rectangles.firstNotNullOf { it.area.takeIf { area -> area >= 50 } } // will fail with NoSuchElementException val evenLargerAreaOrNull = rectangles.firstNotNullOfOrNull { it.area.takeIf { area -> area >= 50 } } println(evenLargerAreaOrNull) // null //sampleEnd }xxxxxxxxxxdata 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 } }println(largeArea) // 18println(largeAreaOrNull) // 18// val evenLargerArea = rectangles.firstNotNullOf { it.area.takeIf { area -> area >= 50 } } // will fail with NoSuchElementExceptionval evenLargerAreaOrNull = rectangles.firstNotNullOfOrNull { it.area.takeIf { area -> area >= 50 } }println(evenLargerAreaOrNull) // null
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