PHP Manual Function Reference Date and Time Related Extensions Date/Time DateTimeImmutable DateTimeImmutable::setISODate DateTimeImmutable::setDate DateTimeImmutable::setTime DateTimeImmutable::setISODate (PHP 5 >= 5.5.0)DateTimeImmutable::setISODate — Sets the ISO date Description public DateTimeImmutable DateTimeImmutable::setISODate ( int $year , int $week [, int $day = 1 ] ) Like DateTime::setISODate() but works with DateTimeImmutable.