Crosscut

Mixing up the concepts of nominal and opaque types may not be a good idea in the first place. And certainly, doing that and having per-field control over visibility are not the only alternatives. What about having both nominal and opaque in the language, as separate concepts?

One takes any type and makes it nominal, as previously proposed. The other takes any type and makes all of its fields (or cases, for a variant?) private. That would allow structural but opaque types, which is a nonsensical combination. But like with anonymous nominal types, that's probably not too bad, as long as it's clear what every feature does.

It's important to remind myself, I'm not looking for a final solution here. That can only come out of a long process of testing and real-world use. What I'm looking for is a sensible first draft. And separate nominal and opaque keywords might be just that.