C++ named requirements: Clock

The Clock requirements describe a bundle consisting of a std::chrono::duration, a std::chrono::time_point, and a function now() to get the current time_point. The origin of the clock's time_point is referred to as the clock's epoch.

Requirements

C1 and C2 denote clock types. t1 and t2 are values returned by C1::now() where the call returning t1 happens before the call returning t2 and both of these calls occur before C1::time_point::max().

Expression	Return type	Operational semantics
C1::rep	An arithmetic type or a class emulating an arithmetic type	The representation type of C1::duration.
C1::period	A specialization of std::ratio	The tick period of the clock in seconds.
C1::duration	std::chrono::duration<C1::rep, C1::period>	The duration type of the clock.
C1::time_point	std::chrono::time_point<C1> or std::chrono::time_point<C2, C1::duration>	The std::chrono::time_point type of the clock. C1 and C2 shall refer to the same epoch.
C1::is_steady	const bool	true if t1 <= t2 is always true and the time between clock ticks is constant, otherwise false
C1::now()	C1::time_point	Returns a time_point object representing the current point in time.