Function format

cpp/src/arrow/util/chrono_internal.h:168–170

// Converts "%H%M" style to C++20's "{:%H%M}" style and uses std::vformat
template <typename Duration>
std::string format(const char* fmt, const Duration& d) {
  return std::vformat(std::string("{:") + fmt + "}", std::make_format_args(d));
}

inline constexpr std::chrono::month jan = std::chrono::January;
inline constexpr std::chrono::month dec = std::chrono::December;