[smasher164]

Sum types overlap a lot with what interfaces over. So enhancing the language with proper sum-types would benefit from enhancing interfaces and switch statements.

However, zero values throw a wrench into this. The zero value of an interface is nil, so enhancing interfaces would require you to address what happens with an uninitialized variable. One of the current proposals suggests that nil continue as the zero value.

They could introduce a totally different type, like a sealed interface, which doesn't require a zero value, but that distinguishes between different types of interfaces, and I'm not sure how that'll be received.