public static function filterBy(Iterator $unfiltered, string $className) : Iterator
    {
        return self::filter($unfiltered, Predicates::instance($className));
    }
public static function filterBy(Iterator $unfiltered, string $className) : Iterator
    {
        return self::filter($unfiltered, Predicates::instance($className));
    }
Returns all instances of class type in unfiltered.
The returned iterator has elements whose class is type or a subclass of type.

@param Iterator $unfiltered
@param string $className
@return Iterator