How would the new "when with guards" ensure exhaustiveness.

# language-evolution

[Pablichjenkov]

How would the new "when with guards" ensure exhaustiveness.

[Davio]

a branch with a guard is ignored for exhaustiveness checks so you'd need to always include an else or don't use guards, but use nested conditions instead

[Alejandro Serrano.Mena]

not exactly, it may be the case that your when is exhaustive even removing the exhaustiveness. For example, you can do

when (val n = ...) {
  null -> ...
  is Int if n > 0 -> ...
  is Int
}

and this would cover every case for n: Int?

[Davio]

well in that case there are 2 cases without guards so they could be taken into account for exhaustiveness checks, so maybe in this case the compiler is smart enough to figure that out, but if that's true, than the last case could be replaced by else and it would be the same thing

[Pablichjenkov]

IMHO not a great addition, the fact that messes up with exhaustiveness, rather confusing