Proof of concept of optimized Set

game/game.go

@@ -59,7 +59,7 @@ func openHub() {
 func resetGame() {
 	title = nil
 	score = newScore()
-	projectiles = &Projectiles{items: newSet[Projectile]()}
+	projectiles = &Projectiles{items: newSet2[Projectile]()}
 	enemies = newEnemies()
 	level = loadLevel()
 	players = loadPlayers()

game/player.go

@@ -122,7 +122,7 @@ func (p *Player) handleButtons(btns firefly.Buttons) {
 			p.pos.X+playerR-bulletD/2,
 			p.pos.Y+playerR-bulletD/2,
 		)
-		bullet := &Projectile{
+		bullet := Projectile{
 			d:   bulletD,
 			dmg: 1,
 		}

game/projectiles.go

@@ -1,26 +1,26 @@
 package game
 
 type Projectiles struct {
-	items *Set[Projectile]
+	items *Set2[Projectile]
 }
 
 func (ps *Projectiles) update() {
-	for i, p := range ps.items.iter() {
-		if p == nil {
+	for i, isSet := range ps.items.iter() {
+		if !isSet {
 			continue
 		}
-		keep := p.update()
+		keep := ps.items.ref(i).update()
 		if !keep {
 			ps.items.remove(i)
 		}
 	}
 }
 
 func (ps Projectiles) render() {
-	for _, p := range ps.items.iter() {
-		if p == nil {
+	for i, isSet := range ps.items.iter() {
+		if !isSet {
 			continue
 		}
-		p.render()
+		ps.items.ref(i).render()
 	}
 }

game/set2.go

@@ -0,0 +1,53 @@
+package game
+
+type Set2[T any] struct {
+	isSet []bool
+	items []T
+}
+
+func newSet2[T any]() *Set2[T] {
+	return &Set2[T]{}
+}
+
+func (s *Set2[T]) add(v T) {
+	for i, isSet := range s.isSet {
+		if !isSet {
+			s.isSet[i] = true
+			s.items[i] = v
+			return
+		}
+	}
+	s.isSet = append(s.isSet, true)
+	s.items = append(s.items, v)
+}
+
+func (s Set2[T]) remove(i int) {
+	s.isSet[i] = false
+}
+
+func (s Set2[T]) len() int {
+	res := 0
+	for _, isSet := range s.isSet {
+		if isSet {
+			res++
+		}
+	}
+	return res
+}
+
+func (s Set2[T]) iter() []bool {
+	return s.isSet
+}
+
+func (s Set2[T]) ref(index int) *T {
+	return &s.items[index]
+}
+
+func (s Set2[T]) empty() bool {
+	for _, isSet := range s.isSet {
+		if isSet {
+			return false
+		}
+	}
+	return true
+}