private function sortByStartDate(Period $interval1, Period $interval2): int
    {
        return $interval1->getStartDate() <=> $interval2->getStartDate();
    }
private function sortByStartDate(Period $interval1, Period $interval2): int
    {
        return $interval1->getStartDate() <=> $interval2->getStartDate();
    }
private function sortByStartDate ( Period $ interval1 , Period $ interval2 ) : int { return $ interval1 -> getStartDate ( ) <=> $ interval2 -> getStartDate ( ) ; }
Sorts two Interval instance using their start datepoint.
Sorts two Interval instance using their start datepoint .