inline fun <R> CharSequence.flatMap(
    transform: (Char) -> Iterable<R>
): List<R>

Returns a single list of all elements yielded from results of transform function being invoked on each character of original char sequence.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val list = listOf("123", "45")
println(list.flatMap { it.toList() }) // [1, 2, 3, 4, 5]
//sampleEnd
}