public function get_extension()
  {
    if ( $this->name ){
      if ( !isset($this->ext) ){
        if ( strpos($this->name, '.') !== false ){
          $p = str::file_ext($this->name, 1);
          $this->ext = $p[1];
          $this->title = $p[0];
        }
        else{
          $this->ext = '';
          $this->title = substr($this->name,-1) === '/' ? substr($this->name,0,-1) : $this->name;
        }
      }
      return $this->ext;
    }
    return false;
  }