Trait parameter overriding question (Scala 3)

[tarsa]

@devlaam

imho the implicit private marker on the type is surprising, for this only applies to types, not to fields.

when main constructor parameter has neither val nor var applied to it then it’s implicitly private and IIRC can be even completely erased if it’s not needed after class initialization. other types of class members (including types) are implicitly public.

@devlaam

Lastly, it feels strange to me that making something public what is private is forbidden by default. We do this all the time. The other way around would not make sense to me indeed. And, it is still possible by a workaround, so why this obstacle?

no, it’s not possible. your workaround is making a non-private field and exposing a path-dependent type based on that non-private field (that’s the crucial part). private[test] is also not fully private as it’s visible outside of the class, so there’s a way to meaningfully use the exposed type, so there’s no need to throw a compilation error.

here’s a simpler example showing the same problem:

class Exposer(param: Int): // no var or val, so `param` is implicitly private
  type ExposedType = param.type // compilation error here
  def expose: ExposedType = param

val exposer = Exposer(5)
val number: exposer.ExposedType = exposer.expose
println(number)

@devlaam

But we are getting off topic here.

yep, probably our posts should be moved to your original thread.