public function check(): bool
  {
    if ( $this->current !== null ){
      // if $on_error is set to E_CONTINUE returns true
      if ( $this->on_error === self::E_CONTINUE ){
        return true;
      }
      // If any connection has an error with mode E_STOP_ALL
      if ( self::$has_error_all && ($this->on_error !== self::E_STOP_ALL) ){
        return false;
      }
      // If this connection has an error with mode E_STOP
      if ( $this->has_error && ($this->on_error !== self::E_STOP) ){
        return false;
      }
      return true;
    }
    return false;
  }