Applying a Label

The problem with implicit labels comes when you have nested calls of the same function type (e.g., a forEach() whose lambda expression contains a forEach()).

You can explicitly label a lambda expression if you like, then use return@ with your custom label.

A label is an identifier plus @, preceding the lambda expression itself:

fun somethingifier(items: List<String>) {
  items.forEach toSender@ {
    if (it.length == 3) return@toSender else println(it)
  }

  println("Done!")
}

fun main() {
  somethingifier(listOf("this", "is", "a", "fun", "bit", "of", "Kotlin"))
}

So, here, we have labeled the lambda expression toSender@, so we can use return@toSender to return from just the lambda expression.

Note that break and continue also support labels, both implicit and custom ones, to help control where they go to.