Kotlin. Java break alternative for when construction

Question

I need break like in Java from when branch. From Kotlin 1.7.0 I get error

when expression must be exhaustive

Now I need to add a branch else. Inside else I want to just exit from when.

I can use a return, but in this case, all the code after the when block will not be executed and we will exit the entire function. Here is an example:

   private fun testFun(a: Int) {
        when(a) {
            5 -> println("this is 5")
            10 -> println("this is 10")
            else -> return 
        }
    
        println("This is end of func") // this will not call
    }

I gave this code snippet as an example. The problem is relevant when using when with enums or boolean.

I can also use this construct: else -> {}. But it doesn't look very clear to me. Please tell me if there is any way to perform default: break; as we did in Java.

Answer 1

First of all, you don't need an else here, as this is a when statement, with the bound value being an Int. It would need to be exhaustive in situations like this

val someValue = when(a) {
    5 -> "this is 5"
    10 -> "this is 10"
    else -> "something else" // now you need the "else" branch
}

So you don't have to write else -> {} in the first place.

That said, if you desperately want to write the word break in here for some reason, you can define:

val `break` = Unit

Now you can do:

// yes, this means you can also do "else -> Unit"
// but if you find "else -> {}" unclear, "else -> Unit" will probably be even more so
else -> `break`

This is super confusing though, since break in Kotlin has type Nothing, rather than Unit. Do this at your own risk.