std::chrono::weekday::weekday
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                    | weekday() = default; | (1) | (since C++20) | 
| explicit constexpr weekday(unsigned wd) noexcept; | (2) | (since C++20) | 
| constexpr weekday(const std::chrono::sys_days& dp) noexcept; | (3) | (since C++20) | 
| explicit constexpr weekday(const std::chrono::local_days& dp) noexcept; | (4) | (since C++20) | 
Constructs a weekday object.
1) Default constructor leaves the weekday value uninitialized.
2) Constructs a 
weekday object holding the weekday value wd. If wd == 7, the value held is 0. If wd > 255, the value held is unspecified.3) Constructs a 
weekday object representing the day of the week dp corresponds to. This constructor defines an implicit conversion from std::chrono::sys_days to weekday.4) Constructs a 
weekday object representing the day of the week dp corresponds to, as if by weekday(std::chrono::sys_days(dp.time_since_epoch())).