class Week {
  private:
    static const char *const *days = { "mon", "tue", "wed", "thur",
                                       "fri", "sat", "sun" };
};

static const char * const days[] = {"mon", "tue", "wed", "thur",
                                       "fri", "sat", "sun"};

static const char * const days[]; //declaration

const char * const Week::days[] = {"mon", "tue", "wed", "thur",
                                       "fri", "sat", "sun"};

constexpr const char* const Week::days[];