widgetPool - switch from map to slice

ui/util/widgetpool.go

@@ -13,23 +13,26 @@ const (
 	WidgetTypeArtistPageHeader
 	WidgetTypePlaylistPageHeader
 	WidgetTypeTracklist
+
+	// keep at bottom
+	numWidgetTypes
 )
 
 // A pool to share commonly-used widgets across pages to reduce
 // creation of new widgets and memory allocations.
 // It is not thread-safe, which is fine for its current use.
 type WidgetPool struct {
-	cache map[WidgetType][]cachedWidget
+	pool [][]pooledWidget
 }
 
-type cachedWidget struct {
+type pooledWidget struct {
 	widget     fyne.CanvasObject
 	releasedAt int64 // unixMillis
 }
 
 func NewWidgetPool() WidgetPool {
 	return WidgetPool{
-		cache: make(map[WidgetType][]cachedWidget),
+		pool: make([][]pooledWidget, numWidgetTypes),
 	}
 }
 
@@ -37,11 +40,11 @@ func NewWidgetPool() WidgetPool {
 // Returns nil if there is no available widget.
 func (w *WidgetPool) Obtain(typ WidgetType) fyne.CanvasObject {
 	var widget fyne.CanvasObject
-	if ws, ok := w.cache[typ]; ok && len(ws) > 0 {
+	if l := len(w.pool[typ]); l > 0 {
-		i := len(ws) - 1
+		i := l - 1
-		widget = ws[i].widget
+		widget = w.pool[typ][i].widget
-		ws[i].widget = nil
+		w.pool[typ][i].widget = nil
-		w.cache[typ] = ws[:i]
+		w.pool[typ] = w.pool[typ][:i]
 	}
 	return widget
 }
@@ -50,10 +53,7 @@ func (w *WidgetPool) Obtain(typ WidgetType) fyne.CanvasObject {
 // The widget must not be modified by the releaser after release,
 // since it may be Obtained for a new use at any time.
 func (w *WidgetPool) Release(typ WidgetType, wid fyne.CanvasObject) {
-	if _, ok := w.cache[typ]; !ok {
+	w.pool[typ] = append(w.pool[typ], pooledWidget{
-		w.cache[typ] = make([]cachedWidget, 0)
-	}
-	w.cache[typ] = append(w.cache[typ], cachedWidget{
 		widget:     wid,
 		releasedAt: time.Now().UnixMilli(),
 	})