Mutually exclusive traits

kpreid:

I don’t know if there are any plans to make negative impls usable to enable otherwise conflicting impls.

AFAIK there's a general "yes, that would be nice" wish for that to eventually be the case, but no concrete plans.

For example, I would like negative impls to replace the concept of fundamental traits, so we could do things like impl !FnOnce for String to solve some of the pattern-related reasons that certain traits are fundamental today.