For - else clause


Requesting else block with loop statement which won’t iterate.

for (i in emptyList<Int>()) {
    // This won't execute
} else {
    // this will executed


forEach modified

fun main(vararg args: String) {
    emptyList<Int>().forElse {
        println("This won't execute")
    } ?: println("this will executed")

fun <T> Collection<T>.forElse(block: (T) -> Unit) = if (isEmpty()) null else forEach(block)


I too have wished for a language to adopt such a feature. I seem to remember some language having such a feature, but I don’t remember which.

There may be some confusion however with other languages. Python has a for-else ( but in that case the else is executed when the loop finishes normally (i.e. no break).


Following the pattern of first() and firstOrNull() methods, might be better to call it forEachOrNull


Also can do

inline fun <T> Collection<T>.forEachOrNull(block: (T) -> Unit) = takeUnless(isEmpty()).forEach(block)


Or you can do something like this:

infix inline fun <T> List<T>.orElse(predicate: () -> Unit){
    if (this.count() == 0) predicate()

infix inline fun <T> List<T>.forElse(predicate: (T) -> Unit) : List<T> {
   	return this

fun main(args: Array<String>) {
    (0 until 0)
    .toList() forElse {
    } orElse {
        println("It's empty")


Using only standard language & stdlib functions it looks Ok and quite readable IMHO:

myList.apply { 
    forEach { 
         println("This executes on each item $it")
    if (isEmpty()) { 
        println("This executes when list is empty")


The issue about this feature is
You can vote for it, if you find it useful. Also, if you could post a concrete example, how would you use that feature, it would make your vote more substantial.


Well how beautiful is Kotlin ?! It allows us to do what we want with what it has, and it has exactly what we want


In this case, we’re lucky that Kotlin can do it with what it has. In many other cases, you can’t. A macro facility would be very nice to have.

(I’m not talking about C-style macros here, but rather something like Lisp or Elixir).