https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62169
--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> --- I was looking at this again in the context of https://cplusplus.github.io/LWG/issue3578 If we ever wanted to make the debug mode iterators SCARY (or if the standard ever required it) then I think we would need to enable implicit conversions between distinct safe iterator types, constrained on them belonging to compatible container types. That way std::set<int>::iterator and std::set<int, std::less<>>::iterator would still be distinct types, but would be _mostly_ interchangeable. Not everything would work though, e.g. anything working with pointers or references to the iterator types would still be incompatible.
