Is there a way to make smart casting work with sealed classe

Question

Is there a way to make smart casting work with sealed classes without having to exhaustively handle every case For instance I expected this to work since I only have two implementations defined for my sealed class

Kirill Zhukov · Answer

I could simply add another `is Failure` handler and it doesn t require to have `else` branch so the way it works right now seems inconsistent

Kirill Zhukov · Answer

More realistic scenario is say I have a sealed class `Result` with only `Success` and `Failure` implementations and I want combine two different results and basically return failure if one of the results is failure and return success otherwise

Kirill Zhukov · Answer

``` sealed class Result object Success Result fun s object Failure Result fun f val r1 Result = Result Success val r2 Result = Result Failure pretend this combines two success results into one final success result fun success r1 Result Success r2 Result Success = Result Success val r Result = when r1 is Result Failure gt Result Failure r2 is Result Failure gt Result Failure r1 is Result Success amp amp r2 is Result Success gt success r1 r2 smart casting works else gt Result Failure shouldn t happen but I have to handle it ```

Kirill Zhukov · Answer

And here s how I expected it to work but it doesn t ``` val r Result = when r1 is Result Failure gt Result Failure r2 is Result Failure gt Result Failure else gt success r1 r2 can t smart cast ```

Dico · Answer

Change `is Result Failure` to ` is Result Success~

Dico · Answer

To allow this would make the smart cast extremely implicit and difficult to read

Dico · Answer

It would also remove the ability to check validity at runtime

Dico · Answer

The compiler adds an else branch if you exhaust the possible cases and that branch will throw an error

Kirill Zhukov · Answer

I guess it s confusing that this doesn t require `else` branch so the compiler does seem to know that there are no more implementations of the class ``` val result Result = Result Failure when result is Result Success gt result s is Result Failure gt result f ```

Dico · Answer

Yeah

Kirill Zhukov · Answer

nice this works ``` val r Result = when r1 is Result Success gt Result Failure r2 is Result Success gt Result Failure else gt success r1 r2 ```

Dico · Answer

You re welcome

Kirill Zhukov · Answer

Thanks