...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::signal::arg
// In header: <boost/signals2/signal.hpp> template<unsigned n> class arg { public: // types typedef Tn type; // The type of the signal's (n+1)th argument };