...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::is_unit_of_system<unit< Dim, System >, System>
// In header: <boost/units/is_unit_of_system.hpp> template<typename Dim, typename System> struct is_unit_of_system<unit< Dim, System >, System> { };