If you need to put in the fallback "else" yourself, with no error or even warning if you forget to do so, it's not much of a guarantee :) (And thinking about t

If you need to put in the fallback "else" yourself, with no error or even warning if you forget to do so, it's not much of a guarantee :) (And thinking about this a bit more, there's presumably also the opposite case: if you add a branch for a type that's not a member of the variant / remove a type from a variant without updating all the visitors, it'd just happily compile with no indication that anything is wrong.)