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kotlinlang

Hello,

I feel I should know this, but why do I need the `else` in this `when`? and please, elaborate on the "type erasure" answer :smile:

```sealed interface Test

class Test1: Test
class Test2: Test

fun <T: Test> T.call() = when (this) {
  is Test1 -> Unit
  is Test2 -> Unit
  else -> throw IllegalArgumentException("why?")
}```
Thanks :slightly_smiling_face:

You theoretically don't need it, but the Kotlin compiler doesn't go that far (yet). There is an issue about this:
<https://youtrack.jetbrains.com/issue/KT-21908/Support-when-exhaustiveness-checking-for-generic-type-parameter-with-sealed-class-upper-bound|https://youtrack.jetbrains.com/issue/KT-21908/Support-when-exhaustiveness-checking-for-generic-type-parameter-with-sealed-class-upper-bound>

And this is going to be fixed in Kotlin 2.1 (if I understand correctly)

thanks, I thought there was going to be a yourtrack already, just did not find myself

If you do `when (this as Test)` It will work then I believe!

uh, trickster :smile: (it does work as expected then)