public function intersect( \PhpSets\Set $set ) {
        $iterator = $set->entries();
        $intersect = new \PhpSets\Set;

        while ( $iterator->valid() ) {
            if ( $this->has( $iterator->current() ) ) {
                $intersect->add( $iterator->current() );
            }
            $iterator->next();
        }
        $iterator->rewind();

        return $intersect;
    }