MaybeIter inbetween

crates/bevy_ecs/src/removal_detection.rs

@@ -4,14 +4,15 @@ use crate::{
     self as bevy_ecs,
     component::{Component, ComponentId, ComponentIdFor},
     entity::Entity,
-    event::{Events, ManualEventReader},
+    event::{Events, ManualEventIterator, ManualEventReader},
     prelude::Local,
     storage::SparseSet,
 };
 use bevy_ecs_macros::SystemParam;
 
 use std::{
     fmt::Debug,
+    iter::Cloned,
     marker::PhantomData,
     ops::{Deref, DerefMut},
 };
@@ -116,13 +117,26 @@ pub struct RemovedComponents<'w, 's, T: Component> {
     event_sets: &'w RemovedComponentEvents,
 }
 
+pub enum MaybeIter<I: Iterator> {
+    Iter(I),
+    Empty,
+}
+
+impl<I: Iterator> Iterator for MaybeIter<I> {
+    type Item = I::Item;
+    fn next(&mut self) -> Option<Self::Item> {
+        match self {
+            MaybeIter::Iter(iter) => iter.next(),
+            MaybeIter::Empty => None,
+        }
+    }
+}
 impl<'w, 's, T: Component> RemovedComponents<'w, 's, T> {
-    pub fn iter(&mut self) -> Box<dyn Iterator<Item = Entity> + '_> {
+    pub fn iter(&mut self) -> MaybeIter<Cloned<ManualEventIterator<'_, Entity>>> {
         if let Some(events) = self.event_sets.get(**self.component_id) {
-            // TODO: Make this an actually name-able type so we don't need to box
-            Box::new(self.reader.iter(events).cloned())
+            MaybeIter::Iter(self.reader.iter(events).cloned())
         } else {
-            Box::new(std::iter::empty())
+            MaybeIter::Empty
         }
     }
 }
@@ -132,7 +146,7 @@ where
     T: Component,
 {
     type Item = Entity;
-    type IntoIter = Box<dyn Iterator<Item = Entity> + 'a>;
+    type IntoIter = MaybeIter<Cloned<ManualEventIterator<'a, Entity>>>;
     fn into_iter(self) -> Self::IntoIter {
         self.iter()
     }