kotlin-stdlib/kotlin.collections/ifEmpty

ifEmpty

inline fun <C : Array<*>, R, R> C.ifEmpty(defaultValue: () -> R): R(source)

Returns this array if it's not empty or the result of calling defaultValue function if the array is empty.

Since Kotlin

1.3

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   val emptyArray: Array<Any> = emptyArray()

val emptyOrNull: Array<Any>? = emptyArray.ifEmpty { null }
println(emptyOrNull) // null

val emptyOrDefault: Array<Any> = emptyArray.ifEmpty { arrayOf("default") }
println(emptyOrDefault.contentToString()) // [default]

val nonEmptyArray = arrayOf(1)
val sameArray = nonEmptyArray.ifEmpty { arrayOf(2) }
println("nonEmptyArray === sameArray is ${nonEmptyArray === sameArray}") // true 
   //sampleEnd
}
inline fun <C : Collection<*>, R, R> C.ifEmpty(defaultValue: () -> R): R(source)

Returns this collection if it's not empty or the result of calling defaultValue function if the collection is empty.

Since Kotlin

1.3

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   val empty: List<Int> = emptyList()

val emptyOrNull: List<Int>? = empty.ifEmpty { null }
println(emptyOrNull) // null

val emptyOrDefault: List<Any> = empty.ifEmpty { listOf("default") }
println(emptyOrDefault) // [default]

val nonEmpty = listOf("x")
val sameList: List<String> = nonEmpty.ifEmpty { listOf("empty") }
println("nonEmpty === sameList is ${nonEmpty === sameList}") // true 
   //sampleEnd
}
inline fun <M : Map<*, *>, R, R> M.ifEmpty(defaultValue: () -> R): R(source)

Returns this map if it's not empty or the result of calling defaultValue function if the map is empty.

Since Kotlin

1.3

Samples

import kotlin.test.*
import java.util.*

fun main() { 
   //sampleStart 
   val emptyMap: Map<String, Int> = emptyMap()

val emptyOrNull = emptyMap.ifEmpty { null }
println(emptyOrNull) // null

val emptyOrDefault: Map<String, Any> = emptyMap.ifEmpty { mapOf("s" to "a") }
println(emptyOrDefault) // {s=a}

val nonEmptyMap = mapOf("x" to 1)
val sameMap = nonEmptyMap.ifEmpty { null }
println("nonEmptyMap === sameMap is ${nonEmptyMap === sameMap}") // true 
   //sampleEnd
}