private final function setReadableWritable(string $mode)
   {
      if (self::MODE_R === $mode) {
          $this->meta["readable"] = true;
          $this->meta["writable"] = false;
      } else if (self::MODE_W === $mode
              || self::MODE_A === $mode
              || self::MODE_C === $mode
              || self::MODE_X === $mode) {
          $this->meta["readable"] = false;
          $this->meta["writable"] = true;
      } else if (self::MODE_R_MORE === $mode
              || self::MODE_W_MORE === $mode    
              || self::MODE_A_MORE === $mode
              || self::MODE_C_MORE === $mode
              || self::MODE_X_MORE === $mode) {
          $this->meta["readable"] = true;
          $this->meta["writable"] = true;
       }
   }