#include <boost/qvm/vec_index.hpp>
namespace boost
{
    namespace qvm
    {
        //Only enabled if:
        //  is_vec<A>::value
        template <class A>
        typename vec_traits<A>::scalar_type
        vec_index_read( A const & a, int i );
    }
}
The i-th element of a.
i >= 0 && i < vec_traits<A>::dim.
This function uses template metaprogramming and can be used even if the optional access function vec_traits<A>::read_element_idx is not available.