Example for World.Mask, showing how check for filter "contains" an …

…entity (#428)
mlange-42 · Sep 10, 2024 · c2a5173 · c2a5173
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,3 +1,9 @@
+## [[unpublished]](https://github.com/mlange-42/arche/compare/v0.13.2...main)
+
+### Documentation
+
+* Adds an example for `World.Mask`, showing how to check whether a filter "contains" an entity (#428)
+
 ## [[v0.13.2]](https://github.com/mlange-42/arche/compare/v0.13.1...v0.13.2)
 
 ### Bugfixes

diff --git a/ecs/entity_test.go b/ecs/entity_test.go
@@ -9,7 +9,7 @@ import (
 )
 
 func TestEntityAsIndex(t *testing.T) {
-	entity := Entity{1, 0}
+	entity := Entity{id: 1}
 	arr := []int{0, 1, 2}
 
 	val := arr[entity.id]

diff --git a/ecs/world_examples_test.go b/ecs/world_examples_test.go
@@ -273,6 +273,26 @@ func ExampleWorld_Batch() {
 	// Output:
 }
 
+func ExampleWorld_Mask() {
+	world := ecs.NewWorld()
+	posID := ecs.ComponentID[Position](&world)
+	velID := ecs.ComponentID[Velocity](&world)
+
+	e1 := world.NewEntity(posID)
+	e2 := world.NewEntity(velID)
+
+	filter := ecs.All(posID)
+
+	// Use the entity's mask to check whether it is in the filter:
+	m1 := world.Mask(e1)
+	m2 := world.Mask(e2)
+	fmt.Println(filter.Matches(&m1))
+	fmt.Println(filter.Matches(&m2))
+	// Output:
+	//true
+	//false
+}
+
 func ExampleWorld_SetListener() {
 	world := ecs.NewWorld()