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

@param IteratorAggregate $unfiltered
@param string $className
@return IteratorAggregate