...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::numeric::functional::promote<ToFrom, ToFrom, std_valarray_tag, std_valarray_tag>
// In header: <boost/accumulators/numeric/functional/valarray.hpp> template<typename ToFrom> struct promote<ToFrom, ToFrom, std_valarray_tag, std_valarray_tag> : public std::unary_function< ToFrom, ToFrom > { // public member functions ToFrom & operator()(ToFrom &) const; };