std::chrono::operator+,std::chrono::operator-(std::chrono::weekday)(3)

NAME
std::chrono::operator+,std::chrono::operator-(std::chrono::weekday) - std::chrono::operator+,std::chrono::operator-(std::chrono::weekday)

Synopsis
   Defined in header <chrono>
   constexpr std::chrono::weekday operator+( const
   std::chrono::weekday& wd, (1) (since C++20)
   const std::chrono::days& d ) noexcept;
   constexpr std::chrono::weekday operator+( const std::chrono::days&
   d, (2) (since C++20)
   const std::chrono::weekday& wd ) noexcept;
   constexpr std::chrono::weekday operator-( const
   std::chrono::weekday& wd, (3) (since C++20)
   const std::chrono::days& d ) noexcept;
   constexpr std::chrono::days operator-( const std::chrono::weekday&
   wd1, (4) (since C++20)
   const std::chrono::weekday& wd2 ) noexcept;
   1-2) Adds d.count() days to wd. The weekday value held in the result is computed by
   first evaluating static_cast<long long>(wd.c_encoding()) + d.count() and reducing it
   modulo 7 to an integer in the range [0, 6].
   3) Subtracts d.count() days from wd. Equivalent to return wd + -d;
   4) If wd1.ok() and wd2.ok() are both true, returns a std::chrono::days value d such
   that d.count() is in the range [0, 6] and wd2 + d == wd1. Otherwise the returned
   value is unspecified.

Return value
   1-3) A std::chrono::weekday holding a weekday value calculated as described above.
   4) A std::chrono::days representing the distance between wd1 and wd2.

Notes
   As long as the computation doesn't overflow, (1-3) always return a valid weekday
   even if wd.ok() is false.

Example
// Run this code
 #include <iostream>
 #include <chrono>
 int main()
 {
     std::cout << std::boolalpha;
     std::chrono::weekday wd {4};
     wd = wd + std::chrono::days(2);
     std::cout << (wd == std::chrono::weekday(6)) << ' '
               << (wd == std::chrono::Saturday) << ' ';
     wd = wd - std::chrono::days(3);
     std::cout << (wd == std::chrono::weekday(3)) << ' '
               << (wd == std::chrono::Wednesday) << ' ';
     wd = std::chrono::Tuesday;
     wd = wd + std::chrono::days{8}; // (((2 + 8) == 10) % 7) == 3;
     std::cout << (wd == std::chrono::Wednesday) << ' ';
     wd = wd + (std::chrono::Sunday - std::chrono::Thursday); // (3 + 3) == 6
     std::cout << (wd == std::chrono::Saturday) << '\n';
 }

Output:
 true true true true true true

See also
   operator++
   operator++(int) increments or decrements the weekday
   operator-- (public member function)
   operator--(int)
   operator+= adds or subtracts a number of days
   operator-= (public member function)