Construct a std::chrono::duration instance with a specified
count.
template <class Rep2> constexpr explicit duration(const Rep2& r);
The internal value of the duration object is initialized with
static_cast<rep>(r).
This constructor only participates in overload resolution if Rep2 is implicitly convertible
to Rep and either
Rep is a floating
point type or Rep2
is not a floating point type.
this->count()==static_cast<rep>(r)
#include <chrono>