An attempt to instantiate a signals2 signal of the form: template <class T> class notification_boost_signal2 { public: boost::signals2::signal<void (const i_some_interface<T> &,boost::optional<T>,T)> sig; }; for notification_boost_signal2<char>, gives the error message in vc++ of: "C:\Programming\VersionControl\boost\boost/signals2/detail/signal_template.hpp(367) : warning C4512: 'boost::signals2::detail::signal3_impl<R,T1,T2,T3,Combiner,Group,GroupCompare,SlotFunction,ExtendedSlotFunction,Mutex>::slot_invoker' : assignment operator could not be generated" There is a huge template trace leading up to this final warning, but before giving it I wonder if anyone knows what it is about ? Perhaps Frank Mori Hess or Douglas Gregor is out there and can tell me what is happening.