call it VisitFunc

engine/billboard.go

@@ -52,7 +52,7 @@ func (b *Billboard) Prepare(g *Game) error {
 }
 
 // Scan visits &b.Src.
-func (b *Billboard) Scan(visit func(interface{}) error) error {
+func (b *Billboard) Scan(visit VisitFunc) error {
 	return visit(&b.Src)
 }
 

engine/camera.go

@@ -86,7 +86,7 @@ func (c *Camera) Prepare(game *Game) error {
 }
 
 // Scan visits c.Child.
-func (c *Camera) Scan(visit func(interface{}) error) error {
+func (c *Camera) Scan(visit VisitFunc) error {
 	return visit(c.Child)
 }
 

engine/container.go

@@ -64,7 +64,7 @@ func (c *Container) Prepare(*Game) error {
 }
 
 // Scan visits every non-nil component in the container.
-func (c *Container) Scan(visit func(interface{}) error) error {
+func (c *Container) Scan(visit VisitFunc) error {
 	for _, x := range c.items {
 		if x != nil {
 			if err := visit(x); err != nil {

engine/drawdag.go

@@ -121,7 +121,7 @@ func (d *DrawDAG) Prepare(game *Game) error {
 }
 
 // Scan visits d.Child.
-func (d *DrawDAG) Scan(visit func(interface{}) error) error {
+func (d *DrawDAG) Scan(visit VisitFunc) error {
 	return visit(d.Child)
 }
 

engine/drawdfs.go

@@ -63,7 +63,7 @@ func (d *DrawDFS) drawRecursive(component interface{}, screen *ebiten.Image, opt
 }
 
 // Scan visits d.Child.
-func (d *DrawDFS) Scan(visit func(interface{}) error) error {
+func (d *DrawDFS) Scan(visit VisitFunc) error {
 	return visit(d.Child)
 }
 

engine/game.go

@@ -162,7 +162,7 @@ func (g *Game) ReversePath(component interface{}) []interface{} {
 //
 // visitPre is visited before descendants, while visitPost is visited after
 // descendants. nil visitors are ignored.
-func (g *Game) Query(ancestor interface{}, behaviour reflect.Type, visitPre, visitPost func(interface{}) error) error {
+func (g *Game) Query(ancestor interface{}, behaviour reflect.Type, visitPre, visitPost VisitFunc) error {
 	pi := reflect.TypeOf(ancestor).Implements(behaviour)
 	if pi && visitPre != nil {
 		if err := visitPre(ancestor); err != nil {
@@ -192,7 +192,7 @@ func (g *Game) Query(ancestor interface{}, behaviour reflect.Type, visitPre, vis
 }
 
 // Scan visits g.Root.
-func (g *Game) Scan(visit func(interface{}) error) error {
+func (g *Game) Scan(visit VisitFunc) error {
 	return visit(g.Root)
 }
 
@@ -425,6 +425,12 @@ func concatOpts(a, b ebiten.DrawImageOptions) ebiten.DrawImageOptions {
 	return a
 }
 
+// VisitFunc callbacks are either provided or called by various Game functions.
+// For example, Query takes two VisitFuncs that are called for each result, and
+// Scan is given a VisitFunc that should be called with each component. For
+// recursive operations, return Skip for components that should be skipped.
+type VisitFunc func(interface{}) error
+
 // Skip is an "error" value that can be returned from visitor callbacks. It
 // tells recursive methods of Game to skip processing the current item and its
 // descendants, but will otherwise continue processing.

engine/interface.go

@@ -149,7 +149,7 @@ type Saver interface {
 // Scan should visit each immediate subcomponent, aborting early if an error is
 // returned from the visitor.
 type Scanner interface {
-	Scan(visit func(interface{}) error) error
+	Scan(visit VisitFunc) error
 }
 
 // Transformer components can provide draw options to apply to themselves and

engine/parallax.go

@@ -39,7 +39,7 @@ func (p *Parallax) Prepare(game *Game) error {
 }
 
 // Scan visits p.Child.
-func (p *Parallax) Scan(visit func(interface{}) error) error {
+func (p *Parallax) Scan(visit VisitFunc) error {
 	return visit(p.Child)
 }
 

engine/prisms.go

@@ -113,7 +113,7 @@ func (m *PrismMap) Prepare(g *Game) error {
 }
 
 // Scan visits &m.Sheet and all Prisms.
-func (m *PrismMap) Scan(visit func(interface{}) error) error {
+func (m *PrismMap) Scan(visit VisitFunc) error {
 	if err := visit(&m.Sheet); err != nil {
 		return err
 	}

engine/scene.go

@@ -39,7 +39,7 @@ type Scene struct {
 }
 
 // Scan visits s.Child.
-func (s *Scene) Scan(visit func(interface{}) error) error {
+func (s *Scene) Scan(visit VisitFunc) error {
 	return visit(s.Child)
 }
 

engine/sheet.go

@@ -47,7 +47,7 @@ func (s *Sheet) Prepare(*Game) error {
 }
 
 // Scan visits &s.Src.
-func (s *Sheet) Scan(visit func(interface{}) error) error {
+func (s *Sheet) Scan(visit VisitFunc) error {
 	return visit(&s.Src)
 }
 

engine/sprite.go

@@ -41,7 +41,7 @@ func (s *Sprite) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 }
 
 // Scan visits &s.Actor and &s.Sheet.
-func (s *Sprite) Scan(visit func(interface{}) error) error {
+func (s *Sprite) Scan(visit VisitFunc) error {
 	if err := visit(&s.Actor); err != nil {
 		return err
 	}

engine/tiles.go

@@ -100,7 +100,7 @@ func (t *Tilemap) Load(fs.FS) error {
 }
 
 // Scan visits &t.Sheet and all tiles.
-func (t *Tilemap) Scan(visit func(interface{}) error) error {
+func (t *Tilemap) Scan(visit VisitFunc) error {
 	if err := visit(&t.Sheet); err != nil {
 		return err
 	}
@@ -155,6 +155,6 @@ type AnimatedTile struct {
 func (a *AnimatedTile) Cell() int { return a.anim.Cell() }
 
 // Scan visits a.anim.
-func (a *AnimatedTile) Scan(visit func(interface{}) error) error {
+func (a *AnimatedTile) Scan(visit VisitFunc) error {
 	return visit(a.anim)
 }

engine/walls.go

@@ -61,7 +61,7 @@ func (w *Wall) CollidesWith(b geom.Box) bool {
 }
 
 // Scan visits &w.Sheet and all WallUnits.
-func (w *Wall) Scan(visit func(interface{}) error) error {
+func (w *Wall) Scan(visit VisitFunc) error {
 	if err := visit(&w.Sheet); err != nil {
 		return err
 	}
@@ -106,7 +106,7 @@ func (u *WallUnit) Draw(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 }
 
 // Scan visits u.Tile.
-func (u *WallUnit) Scan(visit func(interface{}) error) error {
+func (u *WallUnit) Scan(visit VisitFunc) error {
 	return visit(u.Tile)
 }
 

game/aw.go

@@ -259,7 +259,7 @@ func (aw *Awakeman) Prepare(game *engine.Game) error {
 	return nil
 }
 
-func (aw *Awakeman) Scan(visit func(interface{}) error) error {
+func (aw *Awakeman) Scan(visit engine.VisitFunc) error {
 	return visit(&aw.Sprite)
 }
 

game/bubble.go

@@ -55,7 +55,7 @@ func NewBubble(pos geom.Int3) *Bubble {
 	}
 }
 
-func (b *Bubble) Scan(visit func(interface{}) error) error {
+func (b *Bubble) Scan(visit engine.VisitFunc) error {
 	return visit(&b.Sprite)
 }