// pick from two types based on a switch type
    template<typename C0, typename C1, typename V0, typename V1> struct _select
    {
        template<typename S> struct _switch {};

        template<> struct _switch<C0> { typedef V0 result; };
        template<> struct _switch<C1> { typedef V1 result; };
    };

    //example
    typedef typename _select<RowMajor, ColMajor, row_array, col_array>
            ::_switch<ElementLayout>::result storage_array;

    storage_array m;