Use empty structs instead of bools in changes.

cmd/mtwebmapper/tilesupdater.go

@@ -29,7 +29,7 @@ type baseTilesUpdates interface {
 }
 
 type tileUpdater struct {
-	changes      map[xz]bool
+	changes      map[xz]struct{}
 	btu          baseTilesUpdates
 	mapDir       string
 	redisAddress string
@@ -89,7 +89,7 @@ func newTileUpdater(
 		mapDir:       mapDir,
 		redisAddress: redisAddress,
 		ips:          ips,
-		changes:      map[xz]bool{},
+		changes:      map[xz]struct{}{},
 		colors:       colors,
 		bg:           bg,
 		yMin:         int16(yMin),
@@ -146,7 +146,7 @@ func (tu *tileUpdater) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
 	if len(newChanges) > 0 {
 		tu.cond.L.Lock()
 		for _, c := range newChanges {
-			tu.changes[c.quantize()] = true
+			tu.changes[c.quantize()] = struct{}{}
 		}
 		tu.cond.L.Unlock()
 		tu.cond.Signal()
@@ -155,7 +155,7 @@ func (tu *tileUpdater) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
 	rw.WriteHeader(http.StatusOK)
 }
 
-func extractChanges(changes map[xz]bool) []xzc {
+func extractChanges(changes map[xz]struct{}) []xzc {
 	chs := make([]xzc, len(changes))
 	var i int
 	for ch := range changes {
@@ -185,7 +185,7 @@ func (tu *tileUpdater) doUpdates() {
 			tu.cond.Wait()
 		}
 		changes := extractChanges(tu.changes)
-		tu.changes = map[xz]bool{}
+		tu.changes = map[xz]struct{}{}
 		tu.cond.L.Unlock()
 
 		baseDir := filepath.Join(tu.mapDir, "8")