package door type Screen struct { Panels []Panel } func (s *Screen) AddPanel(panel Panel) { s.Panels = append(s.Panels, panel) } func (s *Screen) Output() string { var result string for idx := range s.Panels { result += s.Panels[idx].Output() } return result } func (s *Screen) Update() string { var result string for idx := range s.Panels { result += s.Panels[idx].Update() } return result }