1) What is the required interface for user-defined callbacks?
Hehe it is: http://www.boost.org/doc/libs/1_47_0/doc/html/boost/signals/trackable.html
Ah, so I should provide appropriate visit_each() overload for my callback type? Can't say I understand what it is suppose to do tho. Example for Boost.Function would be great ;)
2) Is it still true that it will be addressed in future versions of Boost.Function?
You've got now Signals2, which allows using weak_ptr for tracking purposes.
Signals2 requires objects to be managed by shared_ptr which imho is more intrusive (in a sense of class design enforcement) than original Signals. My objects are kept in ptr_ and intrusive containers and it is trivial to make them trackable but impossible to make them being managed by shared_ptr. Additionally, within specific sub-systems signal-slot connections are single-threaded and using: namespace bs2 = boost::signals2; using bs2::keywords; bs2::signal_type<void (int), mutex_type<bs2::dummy_mutex> >::type sig; instead of: signal<void(int)> sig; especially multiple times in single class definition is just horrible. Or am I missing some easy way to redefine default mutex? Cheers, Simon