[tsimionescu]

> I’m pretty sure that’s an interface union, not a sum type.

It's a kind of sum type, but it can only be used to constrain types for a generic parameter.

That is, you can define `func foo[T StaticOptional[int]](x T)` and then call it as `foo(StaticNone{})` or `foo(StaticSome[int]{123})`, but you can't do `func foo() StaticOptional[int]` or even `func foo[T StaticOptional[int]]() T {return StaticNone{} }`.

[jchw]

I think that still eats the itab penalty so as long as the structures wind up with the same gcshape? But now I wonder.