16struct WallCoarseClock 
final {
 
   18  using duration = std::chrono::system_clock::duration;
 
   19  using rep = duration::rep;
 
   20  using period = duration::period;
 
   21  using time_point = std::chrono::system_clock::time_point;
 
   23  static constexpr bool is_steady = 
false;
 
   25  static time_point now() 
noexcept;
 
   26  static duration resolution() 
noexcept;