boost::log::operator<<
// In header: <boost/log/utility/manipulators/optional.hpp> template<typename StreamT, typename OptionalT, typename NoneT> unspecified operator<<(StreamT & strm, optional_manipulator< OptionalT, NoneT > const & manip);
Stream output operator for
. Outputs the optional value or the "none" marker, if one was specified on manipulator construction. optional_manipulator