1 files changed, 55 insertions, 2 deletions
diff --git a/ecs/src/event/component.rs b/ecs/src/event/component.rs
index ef09480..ed6b7cf 100644
--- a/ecs/src/event/component.rs
+++ b/ecs/src/event/component.rs
@@ -1,8 +1,12 @@
 //! Component events.
 
 use std::convert::Infallible;
-use std::fmt::Debug;
 
+use crate::component::{Handle as ComponentHandle, HandleMut as ComponentHandleMut};
+use crate::entity::Handle as EntityHandle;
+use crate::pair::Pair;
+use crate::system::observer::EventMatch;
+use crate::util::impl_multiple;
 use crate::Component;
 
 /// Pair relation for events emitted when:
@@ -11,8 +15,57 @@ use crate::Component;
 #[derive(Debug, Component)]
 pub struct Added(Infallible);
 
-/// Pair relation for events emitted when:
+/// Pair relation for events emitted **before**:
 /// a) The target component is removed from a entity.
 /// b) A entity with the target component is despawned.
 #[derive(Debug, Component)]
 pub struct Removed(Infallible);
+
+#[derive(Debug, Component)]
+pub struct Changed(Infallible);
+
+impl_multiple!(
+    EventMatch,
+    (
+        impl<Target: Component> _<'_><Pair<Removed, Target>> (removed),
+        impl<Target: Component> _<'_><Pair<Added, Target>> (added),
+        impl<Target: Component> _<'_><Pair<Changed, Target>> (changed)
+    )
+    cb=(type_params=(observable_type), event_name) => {
+        paste::paste! {
+            #[must_use]
+            pub fn [<get_ $event_name _comp>](&self) -> ComponentHandle<'_, Target>
+            {
+                let ent = self.get_ent_infallible();
+
+                let Some(comp) = ent.get::<Target>() else {
+                    unreachable!();
+                };
+
+                comp
+            }
+
+            #[must_use]
+            pub fn [<get_ $event_name _comp_mut>](&self) -> ComponentHandleMut<'_, Target>
+            {
+                let ent = self.get_ent_infallible();
+
+                let Some(comp) = ent.get_mut::<Target>() else {
+                    unreachable!();
+                };
+
+                comp
+            }
+        }
+
+        #[must_use]
+        pub fn get_ent_infallible(&self) -> EntityHandle<'_>
+        {
+            let Some(ent) = self.get_entity() else {
+                unreachable!();
+            };
+
+            ent
+        }
+    }
+);