...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::signals2::expired_slot — Indicates at least one of a slot's tracked objects has expired.
// In header: <boost/signals2/slot_base.hpp> class expired_slot : public bad_weak_ptr { public: virtual const char * what() const; };