generate type aliases for singleton enum values?

[davidabrahams]

Hello!

Recently I wanted to write code which looked liked this: https://scastie.scala-lang.org/FmYhh8FeQRigeVaW9O42YQ

I have an enum with three cases, and in one branch of logic I know certain cases are impossible, and I wanted to express that in the types. As far as I know the only way to do this is to directly refer to the .types of the singleton values. This leads to ugliness like:

Color.Red.type | Color.Blue.type

I was able to get around this by adding type aliases to the enum's companion: https://scastie.scala-lang.org/vevKe2erRD2jpT1fNN1YMA

object Color:
  type Red = Red.type
  type Blue = Blue.type

This felt like something which dotty could potentially do behind the scenes when compiling enums? I'm not sure how feasible this is or if I'm missing something.