// std::array{ '1','2','3' }
    constexpr auto a_1 = 123_std_char_array;

    // std::array{ '0','x','1','2' }
    constexpr auto a_2 = 0x12_std_char_array;

    // std::array{ '4'.'2','.','1','3' }
    constexpr auto a_3 = 42.13_std_char_array;

template< char ... Chs >
inline constexpr decltype(auto) operator"" _std_char_array( )
{
    // template guide makes this possible
    return  std::array { Chs... } ;
}

// std::array {'S','t','r','i','n','g'}
    constexpr auto std_char_array_buff_ =
         "String"_std_char_array ;

inline auto operator"" _X( const char*, size_t);

constexpr auto string_view_ = "String"sv ;