Proposal for Opaque Type Aliases

Scala Improvement Process
158

I think we’ve gone over this discussion here and in here. The gist is that they are something unique (otherwise we wouldn’t be talking about them) that can be viewed in different ways:

  1. Compile-time wrappers; meaning, they should have better performance than plain wrappers, but on the other hand cannot be instance-checked (as it is a runtime capability).

  2. Abstract type members that are “instantiated” (aliased) only in their local scope (and most likely add functionality via extension methods).

Seeing how their motivation is mainly to implement value classes more efficiently than AnyVal, it’s easier for me to think of them as wrappers.