...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::units::unary_plus_typeof_helper
// In header: <boost/units/operators.hpp> template<typename X> struct unary_plus_typeof_helper { // public member functions typedef typeof((+typeof_::make< X >())) ; };