Is there any way to make Kotlin understand that this `when` kotlinlang #announcements

fun test(x: Int): Int {
        assert(x in 1..3) // doesn't help
        if (x !in 1..3) throw IllegalArgumentException()  // doesn't help
        return when (x) {
            1 -> -1
            2 -> 0
            3 -> 1
        }
    }

Andreas Sinz

05/13/2018, 7:24 PM

nope

arekolek

05/13/2018, 7:24 PM

I guess I can just move the assertion to else

:yes: 3

but I was looking for something like

@IntRange

from support annotations (but to get compile time and runtime precondition check)

Andreas Sinz

05/13/2018, 7:25 PM

yes, I'd just have a

else -> throw Exception

frellan

05/13/2018, 8:10 PM

This is so anoyying, I get that it is a great warning sometimes but yeeech, I just want to use it like a bunch of if statements, not it always beeing exhaustive, currently I have this in my codebase

else -> {}

Andreas Sinz

05/13/2018, 8:25 PM

@frellan non-exhaustive in the sense that you ignore some cases on purpose?

frellan

05/13/2018, 8:30 PM

I have a number, and depending on whether an enum is some types, i multiply that number by different factors, I first define the number and only the types that match should modify it, I used a java switch before migrating my codebase

I dont want to initialise it in every when clause, thats just unnecessary

Andreas Sinz

05/13/2018, 8:45 PM

can you give me a small example?

frellan

05/13/2018, 9:20 PM

var multiplier = 10
when (amount.unit.type) {
  Type.VOLUME -> {
    multiplier *= food.density
  }
  Type.PACKAGE -> {
    multiplier *= food.density
  }
  Type.PIECE -> {
    multiplier *= food.density
  }
  Type.SPECIAL -> {
    multiplier *= food.density
  }
  Type.PORTION -> {
    multiplier *= food.density
  }
  else -> {}
}
return multiplier

Its different for every type, obviously. And there is more types than what I check for but for the rest of them I dont want to modify it

arekolek

05/13/2018, 9:31 PM

In your case I'd do:

return 10 * when(amount.unit.type) {
  Type.VOLUME, Type.PACKAGE, Type.PIECE -> food.density
  Type.SPECIAL -> special.density
  Type.PORTION -> portion.density
  else -> 1
}

(or you could actually list all remaining enum values, instead of

else

, if there's not many of them, I think there's even an intention action that does that for you if you don't have the else branch but you need one)

frellan

05/13/2018, 9:35 PM

Hmm, yeah its an expression, forgot that. Maybe I can do that, thanks for the tip!

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