interface checks like this

engine/animref.go

@@ -8,8 +8,10 @@ import (
 var (
 	animCache = make(map[assetKey]Anim)
 
-	_ Animer = &AnimRef{}
-	_ Loader = &AnimRef{}
+	_ interface {
+		Animer
+		Loader
+	} = &AnimRef{}
 )
 
 func init() {

engine/billboard.go

@@ -8,13 +8,13 @@ import (
 )
 
 // Ensure Billboard satisfies interfaces.
-var (
-	_ Identifier     = &Billboard{}
-	_ Drawer         = &Billboard{}
-	_ DrawOrderer    = &Billboard{}
-	_ ParallaxScaler = &Billboard{}
-	_ Scanner        = &Billboard{}
-)
+var _ interface {
+	Identifier
+	Drawer
+	DrawOrderer
+	ParallaxScaler
+	Scanner
+} = &Billboard{}
 
 func init() {
 	gob.Register(&Billboard{})

engine/camera.go

@@ -8,13 +8,13 @@ import (
 )
 
 // Ensure Camera satisfies interfaces.
-var (
-	_ Identifier = &Camera{}
-	_ Drawer     = &Camera{}
-	_ Prepper    = &Camera{}
-	_ Scanner    = &Camera{}
-	_ Updater    = &Camera{}
-)
+var _ interface {
+	Identifier
+	Drawer
+	Prepper
+	Scanner
+	Updater
+} = &Camera{}
 
 func init() {
 	gob.Register(&Camera{})

engine/debug.go

@@ -9,11 +9,11 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
 )
 
-var (
-	_ Drawer      = PerfDisplay{}
-	_ DrawOrderer = PerfDisplay{}
-	_ Hider       = &PerfDisplay{}
-)
+var _ interface {
+	Drawer
+	DrawOrderer
+	Hider
+} = &PerfDisplay{}
 
 func init() {
 	gob.Register(&PerfDisplay{})

engine/fill.go

@@ -8,7 +8,12 @@ import (
 )
 
 // Ensure Fill satisfies Drawer.
-var _ Drawer = &Fill{}
+var _ interface {
+	Drawer
+	DrawOrderer
+	Hider
+	Identifier
+} = &Fill{}
 
 func init() {
 	gob.Register(Fill{})

engine/sceneref.go

@@ -10,10 +10,10 @@ import (
 )
 
 // Ensure SceneRef satisfies interfaces.
-var (
-	_ Loader = &SceneRef{}
-	_ Scener = &SceneRef{}
-)
+var _ interface {
+	Loader
+	Scener
+} = &SceneRef{}
 
 func init() {
 	gob.Register(SceneRef{})

engine/sheet.go

@@ -6,10 +6,10 @@ import (
 	"github.com/hajimehoshi/ebiten/v2"
 )
 
-var (
-	_ Prepper = &Sheet{}
-	_ Scanner = &Sheet{}
-)
+var _ interface {
+	Prepper
+	Scanner
+} = &Sheet{}
 
 // Sheet handles images that consist of a grid of equally sized regions
 // (cells) and can produce subimages for the cell at an index. This is useful

engine/sprite.go

@@ -8,13 +8,13 @@ import (
 )
 
 // Ensure Sprite satisfies interfaces.
-var (
-	_ Identifier  = &Sprite{}
-	_ Drawer      = &Sprite{}
-	_ DrawOrderer = &Sprite{}
-	_ Scanner     = &Sprite{}
-	_ Updater     = &Sprite{}
-)
+var _ interface {
+	Identifier
+	Drawer
+	DrawOrderer
+	Scanner
+	Updater
+} = &Sprite{}
 
 func init() {
 	gob.Register(&Sprite{})

engine/tiles.go

@@ -8,14 +8,23 @@ import (
 )
 
 // Ensure Tilemap satisfies interfaces.
+var _ interface {
+	Identifier
+	Collider
+	Drawer
+	DrawOrderer
+	Hider
+	Scanner
+	Updater
+} = &Tilemap{}
+
+// Ensure StaticTile and AnimatedTile satisfy Tile.
 var (
-	_ Identifier  = &Tilemap{}
-	_ Collider    = &Tilemap{}
-	_ Drawer      = &Tilemap{}
-	_ DrawOrderer = &Tilemap{}
-	_ Hider       = &Tilemap{}
-	_ Scanner     = &Tilemap{}
-	_ Updater     = &Tilemap{}
+	_ Tile = StaticTile(0)
+	_ interface {
+		Tile
+		Scanner
+	} = AnimatedTile{}
 )
 
 func init() {
@@ -125,13 +134,6 @@ type Tile interface {
 	CellIndex() int
 }
 
-// Ensure StaticTile and AnimatedTile satisfy Tile.
-var (
-	_ Tile    = StaticTile(0)
-	_ Tile    = AnimatedTile{}
-	_ Scanner = AnimatedTile{}
-)
-
 // StaticTile returns a fixed tile index.
 type StaticTile int
 

engine/walls.go

@@ -29,7 +29,7 @@ var (
 // But Wall is still responsible for collisions.
 type Wall struct {
 	ID
-	Ersatz     bool
+	Ersatz     bool        // fake wall - disables collisions
 	Offset     image.Point //  offset the whole wall
 	Sheet      Sheet
 	UnitOffset image.Point // drawing offset