std::chrono::duration<Rep,Period>::duration (3) - Linux Man Pages
constexpr duration() = default; (1) (since C++11)
duration( const duration& ) = default; (2) (since C++11)
template< class Rep2 > (3) (since C++11)
constexpr explicit duration( const Rep2& r );
template< class Rep2, class Period2 > (4) (since C++11)
constexpr duration( const duration<Rep2,Period2>& d );
Constructs a new duration from one of several optional data sources.
1) The default constructor is defaulted.
2) The copy constructor is defaulted (makes a bitwise copy of the tick count).
3) Constructs a duration with r ticks. Note that this constructor only participates in overload resolution if Rep2 (the argument type) is implicitly convertible to rep (the type of this duration's ticks) and
(that is, a duration with an integer tick count cannot be constructed from a floating-point value, but a duration with a floating-point tick count can be constructed from an integer value)
4) Constructs a duration by converting d to an appropriate period and tick count, as if by std::chrono::duration_cast<duration>(d).count(). In order to prevent truncation during conversion, this constructor only participates in overload resolution if computation of the conversion factor (by std::ratio_divide<Period2, Period>) does not overflow and:
(that is, either the duration uses floating-point ticks, or Period2 is exactly divisible by period)
r - a tick count
d - a duration to copy from
The following code shows several examples (both valid and invalid) of how to construct durations:
// Run this code
operator= (public member function)