Demonstrate pattern in example

Author: alice-i-cecile

examples/ecs/component_change_detection.rs

@@ -13,7 +13,7 @@ fn main() {
         .run();
 }
 
-#[derive(Component, Debug)]
+#[derive(Component, PartialEq, Debug)]
 struct MyComponent(f64);
 
 fn setup(mut commands: Commands) {
@@ -25,7 +25,12 @@ fn change_component(time: Res<Time>, mut query: Query<(Entity, &mut MyComponent)
     for (entity, mut component) in &mut query {
         if rand::thread_rng().gen_bool(0.1) {
             info!("changing component {:?}", entity);
-            component.0 = time.seconds_since_startup();
+            let new_component = MyComponent(time.seconds_since_startup().round());
+            // Change detection occurs on mutable derefence,
+            // and does not consider whether or not a value is actually equal.
+            // To avoid triggering change detection when nothing has actually changed,
+            // you can use the `set_if_neq` method on any component or resource that implements PartialEq
+            component.set_if_neq(new_component);
         }
     }
 }