firstNotNullOf

Common
JVM
JS
Native
1.5
inline fun < T , R : Any > Sequence < T > . firstNotNullOf (
transform : ( T ) -> R ?
) : R

(source)

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

The operation is terminal .

import kotlin.test.*

fun main(args: Array<String>) {
//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
}