/* metaclass fro conversation  */
template<size_t x>
class __builder {
private:
    /* generate string type */
    typedef typename num_builder< num_digits(x), x, '\0' >::type type;
    /* string declaration */
    static constexpr type value{};
public:
    /*  */
    static constexpr const char* get();
};
/* instantiate string */
template< size_t x >
constexpr typename __builder< x >::type __builder< x >::value;

template< size_t x >
constexpr const char * __builder< x >::get()
{
    return(value.data);
}

/* compile-time const for converted string */
static constexpr const char* tag = __builder< TAG >::get();