Boost LA

#include <boost/la/vector_access.hpp>

namespace
boost
    {
    namespace
    la
        {
        template <int I>
        -unspecified-return-type- A();
        
        -unspecified-return-type- A0();
        -unspecified-return-type- A1();
        ...
        -unspecified-return-type- A9();
        
        -unspecified-return-type- X();
        -unspecified-return-type- Y();
        -unspecified-return-type- Z();
        -unspecified-return-type- W();
        }
    }