I'd be more worried about early exits from loops in an iterator, e.g. if you had a .any() derived function, or short-circuiting logic in boolean operators with

I'd be more worried about early exits from loops in an iterator, e.g. if you had a .any() derived function, or short-circuiting logic in boolean operators with a lazily evaluated second parameter. A type system won't protect you from that. Or maybe an early return and having an expensive destructor called as it goes out of phase with RAII