code: public static function filterBy(IteratorAggregate $unfiltered, string $className) : IteratorAggregate
      {
          return self::from(Iterators::filterBy(Iterators::from($unfiltered->getIterator()), $className));
      }
docs: Returns all instances of class className in unfiltered.
  
  @param IteratorAggregate $unfiltered
  @param string $className
  @return IteratorAggregate