for _, backend := range u.backends {
		backend.Shutdown()
	}
}

func (u union) String() string {
	var backendStrings []string
	for _, backend := range u.backends {
		backendStrings = append(backendStrings, fmt.Sprintf("%s", backend))
	}
	return fmt.Sprintf("union[%s]", strings.Join(backendStrings, ","))