From 88a33aed4115984d496fcd12a965f9c4aaa0faf6 Mon Sep 17 00:00:00 2001
From: HampusM <hampus@hampusmat.com>
Date: Sun, 12 Oct 2025 17:13:42 +0200
Subject: feat(ecs): emit Removed events before component removal

---
 ecs/examples/component_events.rs | 68 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 ecs/examples/component_events.rs

(limited to 'ecs/examples/component_events.rs')

diff --git a/ecs/examples/component_events.rs b/ecs/examples/component_events.rs
new file mode 100644
index 0000000..4e7335f
--- /dev/null
+++ b/ecs/examples/component_events.rs
@@ -0,0 +1,68 @@
+use ecs::actions::Actions;
+use ecs::component::Component;
+use ecs::event::component::{Changed, Removed};
+use ecs::pair::Pair;
+use ecs::phase::UPDATE;
+use ecs::system::observer::Observe;
+use ecs::{Component, Query, World};
+
+#[derive(Debug, Component)]
+struct CheeseCrumbs
+{
+    cnt: usize,
+}
+
+#[derive(Debug, Component)]
+struct Cheese
+{
+    name: &'static str,
+}
+
+fn eat_cheese(query: Query<(&Cheese, &mut CheeseCrumbs)>, mut actions: Actions)
+{
+    for (cheese_ent_id, (_, mut cheese_crumbs)) in query.iter_with_euids() {
+        println!("Eating cheese!");
+
+        cheese_crumbs.cnt += 40;
+        cheese_crumbs.set_changed();
+
+        actions.remove_components(cheese_ent_id, [Cheese::id()]);
+    }
+}
+
+fn on_cheese_removed(observe: Observe<Pair<Removed, Cheese>>)
+{
+    for evt_match in &observe {
+        let ent = evt_match.get_entity().unwrap();
+
+        let cheese = ent.get::<Cheese>().unwrap();
+
+        println!("{} cheese was eaten", cheese.name);
+    }
+}
+
+fn on_cheese_crumbs_changed(observe: Observe<Pair<Changed, CheeseCrumbs>>)
+{
+    for evt_match in &observe {
+        let ent = evt_match.get_entity().unwrap();
+
+        let cheese_crumbs = ent.get::<CheeseCrumbs>().unwrap();
+
+        println!("Cheese crumbs count changed to {}", cheese_crumbs.cnt);
+    }
+}
+
+fn main()
+{
+    let mut world = World::new();
+
+    world.register_system(*UPDATE, eat_cheese);
+    world.register_observer(on_cheese_removed);
+    world.register_observer(on_cheese_crumbs_changed);
+
+    world.create_entity((Cheese { name: "Brie" }, CheeseCrumbs { cnt: 0 }));
+    world.create_entity((Cheese { name: "Parmesan" }, CheeseCrumbs { cnt: 0 }));
+    world.create_entity((Cheese { name: "Gouda" }, CheeseCrumbs { cnt: 0 }));
+
+    world.step();
+}
-- 
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