code: public function write($uid, $mixed) {
          $fp = @fopen($this->dir . '/' . $uid, 'w+');
          if (!$fp) {
              return false;
          }
          $r = fwrite($fp, serialize($mixed));
          fclose($fp);
          return $r;
      }
docs: Write datas on $uid key
  @param mixed $uid
  @param mixed $mixed