firstNotNullOf

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
}
xxxxxxxxxx
 
​
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 
​
Open in Playground →
Target: JVMRunning on v.2.1.20