问子类std：：chrono：：工期

EN

#include <chrono>

class my_duration : public std::chrono::duration<int64_t, std::milli>
{ /* snip */ };

int main() 
{
    typedef std::chrono::time_point< std::chrono::system_clock, my_duration > my_time_point;
    my_time_point t( my_duration{} );
    //....
}

template<typename _Tp>
  struct __is_duration
  : std::false_type
  { };

template<typename _Rep, typename _Period>
  struct __is_duration<duration<_Rep, _Period>>
  : std::true_type
  { };

//... further down, in time_point: 
static_assert(__is_duration<_Dur>::value,
    "duration must be a specialization of std::chrono::duration");