code: public function clear($uid = null) {
          if ($uid) {
              if (!$this->has($uid)) {
                  return false;
              }
              return @unlink($this->dir . '/' . $uid);
          }
          array_map('unlink', Glob::glob($this->dir . '/*', 0));
          return true;
      }
docs: Clear datas with $uid key
  @param mixed $uid
  @return void