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kotlinlang

Is it possible to return early from an exhaustive `when`?

It should be. A `return` statement is an expression returning `Nothing`.

```val a: Int = when (value) {
    Hello -&gt; 4
    There -&gt; 6
    Bye -&gt; return null
}
return "$a"```

it's not very hard to imagine use cases, e.g. you could have a `when` inside a loop that is used as part of the logic to iterate something, and perhaps one of the cases allows early exit

You could use `break` then. Except in Kotlin/JS, there you should definitely avoid `break` in `when` inside a loop :sweat_smile:

not necessarily, it's two different situations... break is appropriate if you just need to get out of the loop. return is appropriate if you want to get out of the function.

I mean on the one hand I feel like I'm stating the obvious, on the other hand it apparently needs to be stated, so what can I say :slightly_smiling_face:

sorry, yeah the idea is to break out of a when loop early

I know a `return@label` will work for functions, but idk how to label a `when` statement

this could be useful in a scenario where you have nested `when`/`if`s to reduce nesting

```val exhaustive = when {
    exception != null -&gt; {
        if (something) {
            // return out of when early - does not work
            return@when somethingElse 
        }
        // carry on my wayward son
        Result.raise(exception)
    }```

<@U1PEF150S> You can always enclose the when in a run block

Usually though you can refactor so it becomes more elegant than that

If you show a code sample that has the essential elements from your example may be able to suggest something

<@U1UQX3JCC> Why should `break` in `when` be avoided in Kotlin/JS?

<@U3ZLHBTLG> there's an open compiler bug. In KJS it breaks the when, not the loop.

<https://youtrack.jetbrains.com/issue/KT-43943>