constValue for singleton enum cases

[letalvoj]

Let's have an enum

enum E:
  case C

I'd expect one of the following to be possible:

• constValue[E.C.type] should provide C and other parameter-less cases
• Mirror.Sum should have valueOf, the same way how E has valueOf

None of the above is present in dotty as of now.

Use case - I have a bunch of enums for which I want to derive a type-class. The mapping is the very simplest possible - the name of the enum value determines the target instance. Hence the usage of the valueOf, or any other way of instantiating the enum case based on name only.

[bishabosha]

so currently constValue is only for things that have literal types. You can still use Predef.valueOf[E.C.type] or with any other singleton type