Skip iterating over scene entities on default hook

crates/bevy_scene/src/hook.rs

@@ -13,7 +13,7 @@ use bevy_ecs::{
 use crate::{SceneInstance, SceneSpawner};
 
 /// Marker Component for scenes that were hooked.
-#[derive(Component)]
+#[derive(Component, Debug)]
 #[non_exhaustive]
 pub struct SceneHooked;
 
@@ -57,14 +57,9 @@ pub struct SceneHooked;
 /// });
 /// }
 /// ```
-#[derive(Component)]
+#[derive(Component, Default)]
 pub struct SceneHook {
- hook: Box<dyn Hook>,
-}
-impl Default for SceneHook {
- fn default() -> Self {
- Self { hook: Box::new(()) }
- }
+ hook: Option<Box<dyn Hook>>,
 }
 impl<T: Hook> From<T> for SceneHook {
  fn from(hook: T) -> Self {
@@ -79,8 +74,9 @@ impl SceneHook {
  /// that strictly speaking, you might as well pass a closure. Please check
  /// the [`Hook`] trait documentation for details.
  pub fn new<T: Hook>(hook: T) -> Self {
- let hook = Box::new(hook);
- Self { hook }
+ Self {
+ hook: Some(Box::new(hook)),
+ }
  }
 
  /// Same as [`Self::new`] but with type bounds to make it easier to
@@ -155,9 +151,11 @@ pub fn run_hooks(
 ) {
  for (entity, instance, hooked) in unloaded_instances.iter() {
  if let Some(entities) = scene_manager.iter_instance_entities(**instance) {
- for entity_ref in entities.filter_map(|e| world.get_entity(e)) {
- let mut cmd = cmds.entity(entity_ref.id());
- hooked.hook.hook_entity(&entity_ref, &mut cmd);
+ if let Some(hook) = hooked.hook.as_deref() {
+ for entity_ref in entities.filter_map(|e| world.get_entity(e)) {
+ let mut cmd = cmds.entity(entity_ref.id());
+ hook.hook_entity(&entity_ref, &mut cmd);
+ }
  }
  cmds.entity(entity).insert(SceneHooked);
  }
@@ -168,7 +166,3 @@ impl<F: Fn(&EntityRef, &mut EntityCommands) + Send + Sync + 'static> Hook for F
  (self)(entity_ref, commands);
  }
 }
-// This is useful for the `Default` implementation of `SceneBundle`
-impl Hook for () {
- fn hook_entity(&self, _: &EntityRef, _: &mut EntityCommands) {}
-}