code: func (devices *DeviceSet) List() []string {
  	devices.Lock()
  	defer devices.Unlock()
  
  	ids := make([]string, len(devices.Devices))
  	i := 0
  	for k := range devices.Devices {
  		ids[i] = k
  		i++
  	}
  	return ids
  }
docs: // List returns a list of device ids.