...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::log::operator<<
// In header: <boost/log/utility/manipulators/to_log.hpp> template<typename StreamT, typename T, typename TagT> unspecified operator<<(StreamT & strm, to_log_manip< T, TagT > manip);