std::chrono::weekday::operator[](3)

NAME
std::chrono::weekday::operator[] - std::chrono::weekday::operator[]

Synopsis
   constexpr std::chrono::weekday_indexed (1) (since C++20)
       operator[]( unsigned index ) const noexcept;
   constexpr std::chrono::weekday_last (2) (since C++20)
       operator[]( std::chrono::last_spec ) const noexcept;
   1) Constructs a weekday_indexed from *this and index. The result represents the
   index-th weekday in some yet-to-be-specified month. If index is not in the range
   [0, 7] or if !ok() the values (an underlying weekday and an index) held in the
   result are unspecified.
   2) Constructs a weekday_last from *this. The result represents the last weekday in
   some yet-to-be-specified month.

Return value
   1) std::chrono::weekday_indexed(*this, index)
   2) std::chrono::weekday_last(*this)

Example
// Run this code
 #include <chrono>
 #include <iostream>
 using namespace std::chrono;
 int main()
 {
     constexpr auto second_tuesday_in_October_2019 =
         year_month_day{Tuesday[2] / October / 2019y};
     constexpr auto last_tuesday_in_October_2019 =
         year_month_day{Tuesday[last] / October / 2019y};
     std::cout << second_tuesday_in_October_2019 << '\n'
               << last_tuesday_in_October_2019 << '\n';
 }

Possible output:
 2019-10-08
 2019-10-29