Kotools Types/kotools.types.collection/toNotEmptyListOrThrow

toNotEmptyListOrThrow

@ExperimentalSinceKotoolsTypes(version = "4.3.1")

fun <E> Collection<E>.toNotEmptyListOrThrow(): NotEmptyList<E>

Returns a NotEmptyList containing all the elements of this collection, or throws an IllegalArgumentException if this collection is empty.

var collection: Collection<Int> = listOf(1, 2, 3)
var result: NotEmptyList<Int> = collection.toNotEmptyListOrThrow()
println(result) // [1, 2, 3]

collection = emptyList()
collection.toNotEmptyListOrThrow() // IllegalArgumentException

Please note that changes made to the original collection will not be reflected on the resulting NotEmptyList.

val original: MutableCollection<Int> = mutableListOf(1, 2, 3)
val notEmptyList: NotEmptyList<Int> = original.toNotEmptyListOrThrow()
println(original) // [1, 2, 3]
println(notEmptyList) // [1, 2, 3]

original.clear()
println(original) // []
println(notEmptyList) // [1, 2, 3]

You can use the toNotEmptyListOrNull function for returning null instead of throwing an IllegalArgumentException when this collection is empty.