Foundations for EventReader etc Query parameters

Author: alice-i-cecile

crates/bevy_ecs/src/query/event.rs

@@ -0,0 +1,71 @@
+use super::{
+    super::event::{EventReader, EventWriter, Events, ManualEventReader},
+    Access, Fetch, FetchState, FilteredAccess, WorldQuery,
+};
+use crate::{
+    archetype::{Archetype, ArchetypeComponentId},
+    component::{Component, ComponentId},
+    prelude::World,
+    storage::{Table, Tables},
+};
+use std::marker::PhantomData;
+
+impl<'a, T: Component> WorldQuery for EventWriter<'a, T> {
+    type Fetch = EventWriterFetch<T>;
+    type State = EventWriterState<T>;
+}
+
+struct EventWriterFetch<T> {
+    marker: PhantomData<T>,
+}
+
+impl<'a, T: Component> Fetch<'a> for EventWriterFetch<T> {
+    // EventWriter queries return an EventWriter<T> in each item
+    type Item = EventWriter<'a, T>;
+    // This is the corresponding S: FetchState type
+    type State = EventWriterState<T>;
+
+    unsafe fn init(
+        world: &World,
+        state: &Self::State,
+        last_change_tick: u32,
+        change_tick: u32,
+    ) -> Self {
+    }
+
+    fn is_dense(&self) -> bool {}
+
+    unsafe fn set_archetype(
+        &mut self,
+        state: &Self::State,
+        archetype: &Archetype,
+        tables: &Tables,
+    ) {
+    }
+
+    unsafe fn set_table(&mut self, state: &Self::State, table: &Table) {}
+
+    unsafe fn archetype_fetch(&mut self, archetype_index: usize) -> Self::Item {}
+
+    unsafe fn table_fetch(&mut self, table_row: usize) -> Self::Item {}
+}
+struct EventWriterState<T> {
+    marker: PhantomData<T>,
+}
+
+unsafe impl<T: Component> FetchState for EventWriterState<T> {
+    fn init(world: &mut World) -> Self {}
+
+    fn update_component_access(&self, access: &mut FilteredAccess<ComponentId>) {}
+
+    fn update_archetype_component_access(
+        &self,
+        archetype: &Archetype,
+        access: &mut Access<ArchetypeComponentId>,
+    ) {
+    }
+
+    fn matches_archetype(&self, archetype: &Archetype) -> bool {}
+
+    fn matches_table(&self, table: &Table) -> bool {}
+}

crates/bevy_ecs/src/query/mod.rs

@@ -1,4 +1,5 @@
 mod access;
+mod event;
 mod fetch;
 mod filter;
 mod iter;
@@ -9,6 +10,7 @@ pub use fetch::*;
 pub use filter::*;
 pub use iter::*;
 pub use state::*;
+pub use state::*;
 
 #[cfg(test)]
 mod tests {

examples/ecs/per_entity_events.rs

@@ -194,15 +194,14 @@ fn scale_selected(
     }
 }
 
-// FIXME: make this work using `EventWriter<T>` syntax and specialized behavior
 /// Dispatches actions to entities based on the input
 /// Note that we can store several events at once!
 /// Try pressing both "1" and "3" to add 4 to the selected display
 fn input_dispatch(
     // You could also access the &Events<T> component directly
     // then send events to that component with `Events::send`
     mut query: Query<
-        (&mut Events<CycleColorAction>, &mut Events<AddNumberAction>),
+        (EventWriter<CycleColorAction>, EventWriter<AddNumberAction>),
         With<Selectable>,
     >,
     selected: Res<Selected>,
@@ -230,8 +229,7 @@ fn input_dispatch(
 
 fn cycle_color(mut query: Query<(&mut ColorChoices, EventReader<CycleColorAction>)>) {
     for (mut color, action_queue) in query.iter_mut() {
-        let mut reader = action_queue.get_reader();
-        for _ in reader.iter(&action_queue) {
+        for _ in action_queue.iter() {
             *color = color.next().unwrap();
         }
     }