...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<< — Stream output operator.
// In header: <boost/log/utility/value_ref.hpp> template<typename CharT, typename TraitsT, typename T, typename TagT> std::basic_ostream< CharT, TraitsT > & operator<<(std::basic_ostream< CharT, TraitsT > & strm, value_ref< T, TagT > const & val);