...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::accumulators::tag::covariance
template<typename VariateType, typename VariateTag> struct covariance : public boost::accumulators::depends_on< Feature1, Feature2, > { // types typedef accumulators::impl::covariance_impl< mpl::_1, VariateType, VariateTag > impl; };