Frank Mori Hess:
What I'm thinking is more along the lines of how a weak_ptr goes from "expired" to "good". Currently, that can only happen by assignment of a new shared_ptr. And assignment of one expired weak_ptr has no effect on any copies of the weak_ptr, they stay expired.
This is correct as far as it goes. But in the case I showed, no assignment happens to any of the weak_ptr instances. Consider how weak_ptrs go from use_count of 1 to use_count of 0 without any assignment. This is the same event in reverse. It can't normally occur now, of course. Remember that use_count() does not report the state of a particular instance, it reports program-wide state (the number of shared_ptr instances sharing ownership with *this). It can and will go up and down without any changes to *this.
Yes, but in the case of a long-lived signal with many short-lived connections, it would effectively create a resource leak when relying on automatic connection management.
Well, there would be no automatic connection management, so obviously relying on it would be a bad idea. :-) One would have to use scoped connections or manual disconnects in the destructor, as usual.