Update codebase to use IntoIterator where possible. (#5269)

Remove unnecessary calls to `iter()`/`iter_mut()`.
Mainly updates the use of queries in our code, docs, and examples.

```rust
// From
for _ in list.iter() {
for _ in list.iter_mut() {

// To
for _ in &list {
for _ in &mut list {
```

We already enable the pedantic lint [clippy::explicit_iter_loop](https://rust-lang.github.io/rust-clippy/stable/) inside of Bevy. However, this only warns for a few known types from the standard library.

## Note for reviewers
As you can see the additions and deletions are exactly equal.
Maybe give it a quick skim to check I didn't sneak in a crypto miner, but you don't have to torture yourself by reading every line.
I already experienced enough pain making this PR :) 


Co-authored-by: devil-ira <justthecooldude@gmail.com>

benches/benches/bevy_ecs/iteration/iter_simple_system.rs

@@ -30,7 +30,7 @@ impl Benchmark {
         }
 
         fn query_system(mut query: Query<(&Velocity, &mut Position)>) {
-            for (velocity, mut position) in query.iter_mut() {
+            for (velocity, mut position) in &mut query {
                 position.0 += velocity.0;
             }
         }

benches/benches/bevy_ecs/world/commands.rs

@@ -92,7 +92,7 @@ pub fn insert_commands(criterion: &mut Criterion) {
 
         bencher.iter(|| {
             let mut commands = Commands::new(&mut command_queue, &world);
-            for entity in entities.iter() {
+            for entity in &entities {
                 commands
                     .entity(*entity)
                     .insert_bundle((Matrix::default(), Vec3::default()));
@@ -112,7 +112,7 @@ pub fn insert_commands(criterion: &mut Criterion) {
         bencher.iter(|| {
             let mut commands = Commands::new(&mut command_queue, &world);
             let mut values = Vec::with_capacity(entity_count);
-            for entity in entities.iter() {
+            for entity in &entities {
                 values.push((*entity, (Matrix::default(), Vec3::default())));
             }
             commands.insert_or_spawn_batch(values);

benches/benches/bevy_reflect/struct.rs

@@ -43,7 +43,7 @@ fn concrete_struct_field(criterion: &mut Criterion) {
                     .collect::<Vec<_>>();
 
                 bencher.iter(|| {
-                    for name in field_names.iter() {
+                    for name in &field_names {
                         s.field(black_box(name));
                     }
                 });

crates/bevy_animation/src/lib.rs

@@ -183,7 +183,7 @@ pub fn animation_player(
     mut transforms: Query<&mut Transform>,
     children: Query<&Children>,
 ) {
-    for (entity, mut player) in animation_players.iter_mut() {
+    for (entity, mut player) in &mut animation_players {
         if let Some(animation_clip) = animations.get(&player.animation_clip) {
             // Continue if paused unless the `AnimationPlayer` was changed
             // This allow the animation to still be updated if the player.elapsed field was manually updated in pause

crates/bevy_asset/src/asset_server.rs

@@ -110,7 +110,7 @@ impl AssetServer {
     {
         let mut loaders = self.server.loaders.write();
         let loader_index = loaders.len();
-        for extension in loader.extensions().iter() {
+        for extension in loader.extensions() {
             self.server
                 .extension_to_loader_index
                 .write()

crates/bevy_core_pipeline/src/core_3d/mod.rs

@@ -236,7 +236,7 @@ pub fn prepare_core_3d_depth_textures(
     >,
 ) {
     let mut textures = HashMap::default();
-    for (entity, camera) in views_3d.iter() {
+    for (entity, camera) in &views_3d {
         if let Some(physical_target_size) = camera.physical_target_size {
             let cached_texture = textures
                 .entry(camera.target.clone())

crates/bevy_ecs/README.md

@@ -78,7 +78,7 @@ use bevy_ecs::prelude::*;
 struct Position { x: f32, y: f32 }
 
 fn print_position(query: Query<(Entity, &Position)>) {
-    for (entity, position) in query.iter() {
+    for (entity, position) in &query {
         println!("Entity {:?} is at position: x {}, y {}", entity, position.x, position.y);
     }
 }
@@ -130,7 +130,7 @@ struct Velocity { x: f32, y: f32 }
 
 // This system moves each entity with a Position and Velocity component
 fn movement(mut query: Query<(&mut Position, &Velocity)>) {
-    for (mut position, velocity) in query.iter_mut() {
+    for (mut position, velocity) in &mut query {
         position.x += velocity.x;
         position.y += velocity.y;
     }
@@ -176,7 +176,7 @@ struct Alive;
 // Gets the Position component of all Entities with Player component and without the Alive
 // component. 
 fn system(query: Query<&Position, (With<Player>, Without<Alive>)>) {
-    for position in query.iter() {
+    for position in &query {
     }
 }
 ```
@@ -197,13 +197,13 @@ struct Velocity { x: f32, y: f32 }
 
 // Gets the Position component of all Entities whose Velocity has changed since the last run of the System
 fn system_changed(query: Query<&Position, Changed<Velocity>>) {
-    for position in query.iter() {
+    for position in &query {
     }
 }
 
 // Gets the Position component of all Entities that had a Velocity component added since the last run of the System
 fn system_added(query: Query<&Position, Added<Velocity>>) {
-    for position in query.iter() {
+    for position in &query {
     }
 }
 ```

crates/bevy_ecs/examples/change_detection.rs

@@ -79,24 +79,24 @@ fn print_changed_entities(
     entity_with_added_component: Query<Entity, Added<Age>>,
     entity_with_mutated_component: Query<(Entity, &Age), Changed<Age>>,
 ) {
-    for entity in entity_with_added_component.iter() {
+    for entity in &entity_with_added_component {
         println!("    {:?} has it's first birthday!", entity);
     }
-    for (entity, value) in entity_with_mutated_component.iter() {
+    for (entity, value) in &entity_with_mutated_component {
         println!("    {:?} is now {:?} frames old", entity, value);
     }
 }
 
 // This system iterates over all entities and increases their age in every frame
 fn age_all_entities(mut entities: Query<&mut Age>) {
-    for mut age in entities.iter_mut() {
+    for mut age in &mut entities {
         age.frames += 1;
     }
 }
 
 // This system iterates over all entities in every frame and despawns entities older than 2 frames
 fn remove_old_entities(mut commands: Commands, entities: Query<(Entity, &Age)>) {
-    for (entity, age) in entities.iter() {
+    for (entity, age) in &entities {
         if age.frames > 2 {
             println!("    despawning {:?} due to age > 2", entity);
             commands.entity(entity).despawn();

crates/bevy_ecs/macros/src/fetch.rs

@@ -134,7 +134,7 @@ pub fn derive_world_query_impl(ast: DeriveInput) -> TokenStream {
     let mut field_idents = Vec::new();
     let mut field_types = Vec::new();
 
-    for field in fields.iter() {
+    for field in fields {
         let WorldQueryFieldInfo { is_ignored, attrs } = read_world_query_field_info(field);
 
         let field_ident = field.ident.as_ref().unwrap().clone();

crates/bevy_ecs/src/entity/mod.rs

@@ -84,7 +84,7 @@ use std::{
 /// # struct Expired;
 /// #
 /// fn dispose_expired_food(mut commands: Commands, query: Query<Entity, With<Expired>>) {
-///     for food_entity in query.iter() {
+///     for food_entity in &query {
 ///         commands.entity(food_entity).despawn();
 ///     }
 /// }

crates/bevy_ecs/src/query/fetch.rs

@@ -79,7 +79,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 /// }
 ///
 /// fn my_system(query: Query<MyQuery>) {
-///     for q in query.iter() {
+///     for q in &query {
 ///         // Note the type of the returned item.
 ///         let q: MyQueryItem<'_> = q;
 ///         q.foo;
@@ -130,11 +130,11 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 ///
 /// fn my_system(mut health_query: Query<HealthQuery>) {
 ///     // Iterator's item is `HealthQueryReadOnlyItem`.
-///     for health in health_query.iter() {
+///     for health in &health_query {
 ///         println!("Total: {}", health.total());
 ///     }
 ///     // Iterator's item is `HealthQueryItem`.
-///     for mut health in health_query.iter_mut() {
+///     for mut health in &mut health_query {
 ///         health.damage(1.0);
 ///         println!("Total (mut): {}", health.total());
 ///     }
@@ -158,7 +158,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 /// }
 ///
 /// fn my_system(mut my_query: Query<(FooReadOnly, FooReadOnly)>) {
-///     for (i1, i2) in my_query.iter_mut() {
+///     for (i1, i2) in &mut my_query {
 ///         let _: FooReadOnlyItem<'_> = i1;
 ///         let _: FooReadOnlyItem<'_> = i2;
 ///     }
@@ -254,7 +254,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 ///
 /// // You can also compose derived queries with regular ones in tuples.
 /// fn my_system(query: Query<(&Foo, MyQuery, FooQuery)>) {
-///     for (foo, my_query, foo_query) in query.iter() {
+///     for (foo, my_query, foo_query) in &query {
 ///         foo; my_query; foo_query;
 ///     }
 /// }
@@ -279,7 +279,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 /// }
 ///
 /// fn my_system(query: Query<EmptyQuery>) {
-///     for _ in query.iter() {}
+///     for _ in &query {}
 /// }
 ///
 /// # bevy_ecs::system::assert_is_system(my_system);
@@ -311,7 +311,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 /// }
 ///
 /// fn my_system(query: Query<Entity, MyFilter<Foo, Qux>>) {
-///     for _ in query.iter() {}
+///     for _ in &query {}
 /// }
 ///
 /// # bevy_ecs::system::assert_is_system(my_system);
@@ -1087,7 +1087,7 @@ unsafe impl<'w, T: Fetch<'w>> Fetch<'w> for OptionFetch<T> {
 /// # struct Transform {};
 /// #
 /// fn print_moving_objects_system(query: Query<(&Name, ChangeTrackers<Transform>)>) {
-///     for (name, tracker) in query.iter() {
+///     for (name, tracker) in &query {
 ///         if tracker.is_changed() {
 ///             println!("Entity moved: {:?}", name);
 ///         } else {

crates/bevy_ecs/src/query/filter.rs

@@ -36,7 +36,7 @@ use super::ReadOnlyWorldQuery;
 /// # struct Name { name: &'static str };
 /// #
 /// fn compliment_entity_system(query: Query<&Name, With<IsBeautiful>>) {
-///     for name in query.iter() {
+///     for name in &query {
 ///         println!("{} is looking lovely today!", name.name);
 ///     }
 /// }
@@ -177,7 +177,7 @@ impl<T> Copy for WithFetch<T> {}
 /// # struct Name { name: &'static str };
 /// #
 /// fn no_permit_system(query: Query<&Name, Without<Permit>>) {
-///     for name in query.iter() {
+///     for name in &query{
 ///         println!("{} has no permit!", name.name);
 ///     }
 /// }
@@ -324,7 +324,7 @@ impl<T> Copy for WithoutFetch<T> {}
 /// # struct Style {};
 /// #
 /// fn print_cool_entity_system(query: Query<Entity, Or<(Changed<Color>, Changed<Style>)>>) {
-///     for entity in query.iter() {
+///     for entity in &query {
 ///         println!("Entity {:?} got a new style or color", entity);
 ///     }
 /// }
@@ -685,7 +685,7 @@ impl_tick_filter!(
     /// # struct Name {};
     ///
     /// fn print_add_name_component(query: Query<&Name, Added<Name>>) {
-    ///     for name in query.iter() {
+    ///     for name in &query {
     ///         println!("Named entity created: {:?}", name)
     ///     }
     /// }
@@ -725,7 +725,7 @@ impl_tick_filter!(
     /// # struct Transform {};
     ///
     /// fn print_moving_objects_system(query: Query<&Name, Changed<Transform>>) {
-    ///     for name in query.iter() {
+    ///     for name in &query {
     ///         println!("Entity Moved: {:?}", name);
     ///     }
     /// }

crates/bevy_ecs/src/query/state.rs

@@ -264,7 +264,7 @@ impl<Q: WorldQuery, F: WorldQuery> QueryState<Q, F> {
     ///
     /// let mut mutable_component_values = query_state.get_many_mut(&mut world, entities).unwrap();
     ///
-    /// for mut a in mutable_component_values.iter_mut(){
+    /// for mut a in &mut mutable_component_values {
     ///     a.0 += 5;
     /// }
     ///
@@ -1074,7 +1074,7 @@ impl<Q: WorldQuery, F: WorldQuery> QueryState<Q, F> {
 
         let tables = &world.storages.tables;
 
-        for entity in entity_list.into_iter() {
+        for entity in entity_list {
             let location = match world.entities.get(*entity.borrow()) {
                 Some(location) => location,
                 None => continue,

crates/bevy_ecs/src/schedule/executor_parallel.rs

@@ -81,7 +81,7 @@ impl ParallelSystemExecutor for ParallelExecutor {
         self.should_run.grow(systems.len());
 
         // Construct scheduling data for systems.
-        for container in systems.iter() {
+        for container in systems {
             let dependencies_total = container.dependencies().len();
             let system = container.system();
             let (start_sender, start_receiver) = async_channel::bounded(1);

crates/bevy_ecs/src/storage/table.rs

@@ -492,7 +492,7 @@ impl Tables {
             .from_key(component_ids)
             .or_insert_with(|| {
                 let mut table = Table::with_capacity(0, component_ids.len());
-                for component_id in component_ids.iter() {
+                for component_id in component_ids {
                     table.add_column(components.get_info_unchecked(*component_id));
                 }
                 tables.push(table);

crates/bevy_ecs/src/system/commands/parallel_scope.rs

@@ -75,7 +75,7 @@ unsafe impl SystemParamState for ParallelCommandsState {
     }
 
     fn apply(&mut self, world: &mut World) {
-        for cq in self.thread_local_storage.iter_mut() {
+        for cq in &mut self.thread_local_storage {
             cq.get_mut().apply(world);
         }
     }

crates/bevy_ecs/src/system/exclusive_system.rs

@@ -128,7 +128,7 @@ mod tests {
             query: Query<Entity, With<Foo>>,
             mut counter: ResMut<usize>,
         ) {
-            for entity in query.iter() {
+            for entity in &query {
                 *counter += 1;
                 commands.entity(entity).remove::<Foo>();
             }

crates/bevy_ecs/src/system/function_system.rs

@@ -126,7 +126,7 @@ impl SystemMeta {
 /// world.resource_scope(|world, mut cached_state: Mut<CachedSystemState>| {
 ///     let mut event_reader = cached_state.event_state.get_mut(world);
 ///
-///     for events in event_reader.iter(){
+///     for events in event_reader.iter() {
 ///         println!("Hello World!");
 ///     };
 /// });

crates/bevy_ecs/src/system/mod.rs

@@ -23,7 +23,7 @@
 //!     mut query: Query<(&Player, &mut Score)>,
 //!     mut round: ResMut<Round>,
 //! ) {
-//!     for (player, mut score) in query.iter_mut() {
+//!     for (player, mut score) in &mut query {
 //!         if player.alive {
 //!             score.0 += round.0;
 //!         }
@@ -135,7 +135,7 @@ mod tests {
     #[test]
     fn simple_system() {
         fn sys(query: Query<&A>) {
-            for a in query.iter() {
+            for a in &query {
                 println!("{:?}", a);
             }
         }
@@ -598,7 +598,7 @@ mod tests {
             mut modified: ResMut<bool>,
         ) {
             assert_eq!(query.iter().count(), 1, "entity exists");
-            for entity in query.iter() {
+            for entity in &query {
                 let location = entities.get(entity).unwrap();
                 let archetype = archetypes.get(location.archetype_id).unwrap();
                 let archetype_components = archetype.components().collect::<Vec<_>>();

crates/bevy_ecs/src/system/query.rs

@@ -211,7 +211,7 @@ use std::{any::TypeId, borrow::Borrow, fmt::Debug};
 /// # #[derive(Component)]
 /// # struct ComponentB;
 /// fn immutable_query_system(query: Query<(&ComponentA, &ComponentB)>) {
-///     for (a, b) in query.iter() {
+///     for (a, b) in &query {
 ///         // Here, `a` and `b` are normal references to components, relatively of
 ///         // `&ComponentA` and `&ComponentB` types.
 ///     }
@@ -219,7 +219,7 @@ use std::{any::TypeId, borrow::Borrow, fmt::Debug};
 /// # bevy_ecs::system::assert_is_system(immutable_query_system);
 ///
 /// fn mutable_query_system(mut query: Query<(&mut ComponentA, &ComponentB)>) {
-///     for (mut a, b) in query.iter_mut() {
+///     for (mut a, b) in &mut query {
 ///         // Similar to the above system, but this time `ComponentA` can be accessed mutably.
 ///         // Note the usage of `mut` in the tuple and the call to `iter_mut` instead of `iter`.
 ///     }
@@ -285,7 +285,7 @@ impl<'w, 's, Q: WorldQuery, F: WorldQuery> Query<'w, 's, Q, F> {
     /// # struct Player { name: String }
     /// #
     /// fn report_names_system(query: Query<&Player>) {
-    ///     for player in query.iter() {
+    ///     for player in &query {
     ///         println!("Say hello to {}!", player.name);
     ///     }
     /// }
@@ -315,7 +315,7 @@ impl<'w, 's, Q: WorldQuery, F: WorldQuery> Query<'w, 's, Q, F> {
     /// # struct Velocity { x: f32, y: f32, z: f32 }
     /// fn gravity_system(mut query: Query<&mut Velocity>) {
     ///     const DELTA: f32 = 1.0 / 60.0;
-    ///     for mut velocity in query.iter_mut() {
+    ///     for mut velocity in &mut query {
     ///         velocity.y -= 9.8 * DELTA;
     ///     }
     /// }
@@ -782,7 +782,7 @@ impl<'w, 's, Q: WorldQuery, F: WorldQuery> Query<'w, 's, Q, F> {
     /// }
     ///
     /// fn check_all_targets_in_range(targeting_query: Query<(Entity, &Targets, &Position)>, targets_query: Query<&Position>){
-    ///     for (targeting_entity, targets, origin) in targeting_query.iter(){
+    ///     for (targeting_entity, targets, origin) in &targeting_query {
     ///         // We can use "destructuring" to unpack the results nicely
     ///         let [target_1, target_2, target_3] = targets_query.many(targets.0);
     ///
@@ -885,7 +885,7 @@ impl<'w, 's, Q: WorldQuery, F: WorldQuery> Query<'w, 's, Q, F> {
     /// }
     ///
     /// fn spring_forces(spring_query: Query<&Spring>, mut mass_query: Query<(&Position, &mut Force)>){
-    ///     for spring in spring_query.iter(){
+    ///     for spring in &spring_query {
     ///          // We can use "destructuring" to unpack our query items nicely
     ///          let [(position_1, mut force_1), (position_2, mut force_2)] = mass_query.many_mut(spring.connected_entities);
     ///
@@ -1375,7 +1375,7 @@ impl<'w, 's, Q: ReadOnlyWorldQuery, F: WorldQuery> Query<'w, 's, Q, F> {
     /// # struct Player { name: String }
     /// #
     /// fn report_names_system(query: Query<&Player>) {
-    ///     for player in query.iter() {
+    ///     for player in &query {
     ///         println!("Say hello to {}!", player.name);
     ///     }
     /// }

crates/bevy_hierarchy/src/components/children.rs

@@ -17,7 +17,7 @@ pub struct Children(pub(crate) SmallVec<[Entity; 8]>);
 
 impl MapEntities for Children {
     fn map_entities(&mut self, entity_map: &EntityMap) -> Result<(), MapEntitiesError> {
-        for entity in self.0.iter_mut() {
+        for entity in &mut self.0 {
             *entity = entity_map.get(*entity)?;
         }
 

crates/bevy_pbr/src/light.rs

@@ -459,7 +459,7 @@ pub fn add_clusters(
     mut commands: Commands,
     cameras: Query<(Entity, Option<&ClusterConfig>), (With<Camera>, Without<Clusters>)>,
 ) {
-    for (entity, config) in cameras.iter() {
+    for (entity, config) in &cameras {
         let config = config.copied().unwrap_or_default();
         // actual settings here don't matter - they will be overwritten in assign_lights_to_clusters
         commands
@@ -901,7 +901,7 @@ pub(crate) fn assign_lights_to_clusters(
     }
 
     for (view_entity, camera_transform, camera, frustum, config, clusters, mut visible_lights) in
-        views.iter_mut()
+        &mut views
     {
         let clusters = clusters.into_inner();
 
@@ -1420,7 +1420,7 @@ pub fn update_directional_light_frusta(
         Or<(Changed<GlobalTransform>, Changed<DirectionalLight>)>,
     >,
 ) {
-    for (transform, directional_light, mut frustum, visibility) in views.iter_mut() {
+    for (transform, directional_light, mut frustum, visibility) in &mut views {
         // The frustum is used for culling meshes to the light for shadow mapping
         // so if shadow mapping is disabled for this light, then the frustum is
         // not needed.
@@ -1454,7 +1454,7 @@ pub fn update_point_light_frusta(
         .map(|CubeMapFace { target, up }| GlobalTransform::identity().looking_at(*target, *up))
         .collect::<Vec<_>>();
 
-    for (entity, transform, point_light, mut cubemap_frusta) in views.iter_mut() {
+    for (entity, transform, point_light, mut cubemap_frusta) in &mut views {
         // The frusta are used for culling meshes to the light for shadow mapping
         // so if shadow mapping is disabled for this light, then the frusta are
         // not needed.
@@ -1559,7 +1559,7 @@ pub fn check_light_mesh_visibility(
 ) {
     // Directonal lights
     for (directional_light, frustum, mut visible_entities, maybe_view_mask, visibility) in
-        directional_lights.iter_mut()
+        &mut directional_lights
     {
         visible_entities.entities.clear();
 
@@ -1577,7 +1577,7 @@ pub fn check_light_mesh_visibility(
             maybe_entity_mask,
             maybe_aabb,
             maybe_transform,
-        ) in visible_entity_query.iter_mut()
+        ) in &mut visible_entity_query
         {
             if !visibility.is_visible {
                 continue;
@@ -1603,7 +1603,7 @@ pub fn check_light_mesh_visibility(
         // to prevent holding unneeded memory
     }
 
-    for visible_lights in visible_point_lights.iter() {
+    for visible_lights in &visible_point_lights {
         for light_entity in visible_lights.entities.iter().copied() {
             // Point lights
             if let Ok((
@@ -1636,7 +1636,7 @@ pub fn check_light_mesh_visibility(
                     maybe_entity_mask,
                     maybe_aabb,
                     maybe_transform,
-                ) in visible_entity_query.iter_mut()
+                ) in &mut visible_entity_query
                 {
                     if !visibility.is_visible {
                         continue;

crates/bevy_pbr/src/material.rs

@@ -333,7 +333,7 @@ pub fn queue_material_meshes<M: Material>(
     M::Data: PartialEq + Eq + Hash + Clone,
 {
     for (view, visible_entities, mut opaque_phase, mut alpha_mask_phase, mut transparent_phase) in
-        views.iter_mut()
+        &mut views
     {
         let draw_opaque_pbr = opaque_draw_functions
             .read()

crates/bevy_pbr/src/render/light.rs

@@ -885,7 +885,7 @@ pub fn prepare_lights(
         .write_buffer(&render_device, &render_queue);
 
     // set up light data for each view
-    for (entity, extracted_view, clusters) in views.iter() {
+    for (entity, extracted_view, clusters) in &views {
         let point_light_depth_texture = texture_cache.get(
             &render_device,
             TextureDescriptor {
@@ -1482,7 +1482,7 @@ pub fn prepare_clusters(
         mesh_pipeline.clustered_forward_buffer_binding_type,
         BufferBindingType::Storage { .. }
     );
-    for (entity, cluster_config, extracted_clusters) in views.iter() {
+    for (entity, cluster_config, extracted_clusters) in &views {
         let mut view_clusters_bindings =
             ViewClusterBindings::new(mesh_pipeline.clustered_forward_buffer_binding_type);
         view_clusters_bindings.clear();
@@ -1562,7 +1562,7 @@ pub fn queue_shadows(
     directional_light_entities: Query<&VisibleEntities, With<ExtractedDirectionalLight>>,
     spot_light_entities: Query<&VisibleEntities, With<ExtractedPointLight>>,
 ) {
-    for view_lights in view_lights.iter() {
+    for view_lights in &view_lights {
         let draw_shadow_mesh = shadow_draw_functions
             .read()
             .get_id::<DrawShadowMesh>()

crates/bevy_pbr/src/render/mesh.rs

@@ -753,7 +753,7 @@ pub fn queue_mesh_view_bind_groups(
         light_meta.view_gpu_lights.binding(),
         global_light_meta.gpu_point_lights.binding(),
     ) {
-        for (entity, view_shadow_bindings, view_cluster_bindings) in views.iter() {
+        for (entity, view_shadow_bindings, view_cluster_bindings) in &views {
             let view_bind_group = render_device.create_bind_group(&BindGroupDescriptor {
                 entries: &[
                     BindGroupEntry {

crates/bevy_pbr/src/wireframe.rs

@@ -51,7 +51,7 @@ impl Plugin for WireframePlugin {
 }
 
 fn extract_wireframes(mut commands: Commands, query: Query<Entity, With<Wireframe>>) {
-    for entity in query.iter() {
+    for entity in &query {
         commands.get_or_spawn(entity).insert(Wireframe);
     }
 }
@@ -118,7 +118,7 @@ fn queue_wireframes(
         .get_id::<DrawWireframes>()
         .unwrap();
     let msaa_key = MeshPipelineKey::from_msaa_samples(msaa.samples);
-    for (view, visible_entities, mut opaque_phase) in views.iter_mut() {
+    for (view, visible_entities, mut opaque_phase) in &mut views {
         let rangefinder = view.rangefinder3d();
 
         let add_render_phase =

crates/bevy_reflect/bevy_reflect_derive/src/field_attributes.rs

@@ -103,7 +103,7 @@ fn parse_meta(args: &mut ReflectFieldAttr, meta: &Meta) -> Result<(), syn::Error
             Err(syn::Error::new(list.path.span(), "unexpected property"))
         }
         Meta::List(list) => {
-            for nested in list.nested.iter() {
+            for nested in &list.nested {
                 if let NestedMeta::Meta(meta) = nested {
                     parse_meta(args, meta)?;
                 }

crates/bevy_render/src/camera/camera.rs

@@ -362,10 +362,10 @@ pub fn camera_system<T: CameraProjection + Component>(
         .collect();
 
     let mut added_cameras = vec![];
-    for entity in &mut queries.p1().iter() {
+    for entity in &queries.p1() {
         added_cameras.push(entity);
     }
-    for (entity, mut camera, mut camera_projection) in queries.p0().iter_mut() {
+    for (entity, mut camera, mut camera_projection) in &mut queries.p0() {
         if camera
             .target
             .is_changed(&changed_window_ids, &changed_image_handles)

crates/bevy_render/src/mesh/mesh/mod.rs

@@ -465,7 +465,7 @@ impl InnerMeshVertexBufferLayout {
         attribute_descriptors: &[VertexAttributeDescriptor],
     ) -> Result<VertexBufferLayout, MissingVertexAttributeError> {
         let mut attributes = Vec::with_capacity(attribute_descriptors.len());
-        for attribute_descriptor in attribute_descriptors.iter() {
+        for attribute_descriptor in attribute_descriptors {
             if let Some(index) = self
                 .attribute_ids
                 .iter()

crates/bevy_render/src/render_phase/mod.rs

@@ -63,14 +63,14 @@ impl<I: BatchedPhaseItem> RenderPhase<I> {
 
 /// This system sorts all [`RenderPhases`](RenderPhase) for the [`PhaseItem`] type.
 pub fn sort_phase_system<I: PhaseItem>(mut render_phases: Query<&mut RenderPhase<I>>) {
-    for mut phase in render_phases.iter_mut() {
+    for mut phase in &mut render_phases {
         phase.sort();
     }
 }
 
 /// This system batches the [`PhaseItem`]s of all [`RenderPhase`]s of this type.
 pub fn batch_phase_system<I: BatchedPhaseItem>(mut render_phases: Query<&mut RenderPhase<I>>) {
-    for mut phase in render_phases.iter_mut() {
+    for mut phase in &mut render_phases {
         phase.batch();
     }
 }

crates/bevy_render/src/view/mod.rs

@@ -149,7 +149,7 @@ fn prepare_view_uniforms(
     views: Query<(Entity, &ExtractedView)>,
 ) {
     view_uniforms.uniforms.clear();
-    for (entity, camera) in views.iter() {
+    for (entity, camera) in &views {
         let projection = camera.projection;
         let inverse_projection = projection.inverse();
         let view = camera.transform.compute_matrix();
@@ -187,7 +187,7 @@ fn prepare_view_targets(
     cameras: Query<(Entity, &ExtractedCamera)>,
 ) {
     let mut sampled_textures = HashMap::default();
-    for (entity, camera) in cameras.iter() {
+    for (entity, camera) in &cameras {
         if let Some(target_size) = camera.physical_target_size {
             if let Some(texture_view) = camera.target.get_texture_view(&windows, &images) {
                 let sampled_target = if msaa.samples > 1 {

crates/bevy_render/src/view/visibility/mod.rs

@@ -139,7 +139,7 @@ pub fn calculate_bounds(
     meshes: Res<Assets<Mesh>>,
     without_aabb: Query<(Entity, &Handle<Mesh>), (Without<Aabb>, Without<NoFrustumCulling>)>,
 ) {
-    for (entity, mesh_handle) in without_aabb.iter() {
+    for (entity, mesh_handle) in &without_aabb {
         if let Some(mesh) = meshes.get(mesh_handle) {
             if let Some(aabb) = mesh.compute_aabb() {
                 commands.entity(entity).insert(aabb);
@@ -151,7 +151,7 @@ pub fn calculate_bounds(
 pub fn update_frusta<T: Component + CameraProjection + Send + Sync + 'static>(
     mut views: Query<(&GlobalTransform, &T, &mut Frustum)>,
 ) {
-    for (transform, projection, mut frustum) in views.iter_mut() {
+    for (transform, projection, mut frustum) in &mut views {
         let view_projection =
             projection.get_projection_matrix() * transform.compute_matrix().inverse();
         *frustum = Frustum::from_view_projection(
@@ -189,7 +189,7 @@ pub fn check_visibility(
         computed_visibility.is_visible = false;
     }
 
-    for (mut visible_entities, frustum, maybe_view_mask) in view_query.iter_mut() {
+    for (mut visible_entities, frustum, maybe_view_mask) in &mut view_query {
         let view_mask = maybe_view_mask.copied().unwrap_or_default();
         visible_entities.entities.clear();
         visible_entity_query.p1().par_for_each_mut(

crates/bevy_scene/src/bundle.rs

@@ -53,7 +53,7 @@ pub fn scene_spawner(
     >,
     mut scene_spawner: ResMut<SceneSpawner>,
 ) {
-    for (entity, scene, instance) in scene_to_spawn.iter_mut() {
+    for (entity, scene, instance) in &mut scene_to_spawn {
         let new_instance = scene_spawner.spawn_as_child(scene.clone(), entity);
         if let Some(mut old_instance) = instance {
             scene_spawner.despawn_instance(**old_instance);
@@ -62,7 +62,7 @@ pub fn scene_spawner(
             commands.entity(entity).insert(SceneInstance(new_instance));
         }
     }
-    for (entity, dynamic_scene, instance) in dynamic_scene_to_spawn.iter_mut() {
+    for (entity, dynamic_scene, instance) in &mut dynamic_scene_to_spawn {
         let new_instance = scene_spawner.spawn_dynamic_as_child(dynamic_scene.clone(), entity);
         if let Some(mut old_instance) = instance {
             scene_spawner.despawn_instance(**old_instance);

crates/bevy_scene/src/scene_spawner.rs

@@ -227,7 +227,7 @@ impl SceneSpawner {
     ) -> Result<(), SceneSpawnError> {
         for scene_handle in scene_handles {
             if let Some(spawned_instances) = self.spawned_dynamic_scenes.get(scene_handle) {
-                for instance_id in spawned_instances.iter() {
+                for instance_id in spawned_instances {
                     if let Some(instance_info) = self.spawned_instances.get_mut(instance_id) {
                         Self::spawn_dynamic_internal(
                             world,

crates/bevy_scene/src/serde.rs

@@ -71,7 +71,7 @@ impl<'a> Serialize for ComponentsSerializer<'a> {
         S: serde::Serializer,
     {
         let mut state = serializer.serialize_seq(Some(self.components.len()))?;
-        for component in self.components.iter() {
+        for component in self.components {
             state.serialize_element(&ReflectSerializer::new(
                 &**component,
                 &*self.registry.read(),

crates/bevy_sprite/src/mesh2d/material.rs

@@ -310,7 +310,7 @@ pub fn queue_material2d_meshes<M: SpecializedMaterial2d>(
         return;
     }
     let render_device = render_device.into_inner();
-    for (visible_entities, mut transparent_phase) in views.iter_mut() {
+    for (visible_entities, mut transparent_phase) in &mut views {
         let draw_transparent_pbr = transparent_draw_functions
             .read()
             .get_id::<DrawMaterial2d<M>>()

crates/bevy_sprite/src/mesh2d/mesh.rs

@@ -408,7 +408,7 @@ pub fn queue_mesh2d_view_bind_groups(
     views: Query<Entity, With<ExtractedView>>,
 ) {
     if let Some(view_binding) = view_uniforms.uniforms.binding() {
-        for entity in views.iter() {
+        for entity in &views {
             let view_bind_group = render_device.create_bind_group(&BindGroupDescriptor {
                 entries: &[BindGroupEntry {
                     binding: 0,

crates/bevy_sprite/src/render/mod.rs

@@ -389,7 +389,7 @@ pub fn queue_sprites(
         let mut colored_index = 0;
 
         // FIXME: VisibleEntities is ignored
-        for mut transparent_phase in views.iter_mut() {
+        for mut transparent_phase in &mut views {
             let extracted_sprites = &mut extracted_sprites.sprites;
             let image_bind_groups = &mut *image_bind_groups;
 
@@ -420,7 +420,7 @@ pub fn queue_sprites(
             // Compatible items share the same entity.
             // Batches are merged later (in `batch_phase_system()`), so that they can be interrupted
             // by any other phase item (and they can interrupt other items from batching).
-            for extracted_sprite in extracted_sprites.iter() {
+            for extracted_sprite in extracted_sprites {
                 let new_batch = SpriteBatch {
                     image_handle_id: extracted_sprite.image_handle_id,
                     colored: extracted_sprite.color != Color::WHITE,

crates/bevy_text/src/text2d.rs

@@ -147,7 +147,7 @@ pub fn update_text2d_layout(
     let factor_changed = scale_factor_changed.iter().last().is_some();
     let scale_factor = windows.scale_factor(WindowId::primary());
 
-    for (entity, text_changed, text, maybe_bounds, mut calculated_size) in text_query.iter_mut() {
+    for (entity, text_changed, text, maybe_bounds, mut calculated_size) in &mut text_query {
         if factor_changed || text_changed || queue.remove(&entity) {
             let text_bounds = match maybe_bounds {
                 Some(bounds) => Vec2::new(

crates/bevy_transform/src/systems.rs

@@ -34,7 +34,7 @@ pub fn transform_propagate_system(
         if let Some((children, changed_children)) = children {
             // If our `Children` has changed, we need to recalculate everything below us
             changed |= changed_children;
-            for child in children.iter() {
+            for child in children {
                 let _ = propagate_recursive(
                     &global_transform,
                     &mut transform_query,
@@ -80,7 +80,7 @@ fn propagate_recursive(
     let (children, changed_children) = children_query.get(entity).map_err(drop)?;
     // If our `Children` has changed, we need to recalculate everything below us
     changed |= changed_children;
-    for child in children.iter() {
+    for child in children {
         let _ = propagate_recursive(
             &global_matrix,
             transform_query,

crates/bevy_ui/src/flex/mod.rs

@@ -112,7 +112,7 @@ impl FlexSurface {
 
     pub fn update_children(&mut self, entity: Entity, children: &Children) {
         let mut taffy_children = Vec::with_capacity(children.len());
-        for child in children.iter() {
+        for child in children {
             if let Some(taffy_node) = self.entity_to_taffy.get(child) {
                 taffy_children.push(*taffy_node);
             } else {
@@ -231,7 +231,7 @@ pub fn flex_node_system(
         query: Query<(Entity, &Style, Option<&CalculatedSize>), F>,
     ) {
         // update changed nodes
-        for (entity, style, calculated_size) in query.iter() {
+        for (entity, style, calculated_size) in &query {
             // TODO: remove node from old hierarchy if its root has changed
             if let Some(calculated_size) = calculated_size {
                 flex_surface.upsert_leaf(entity, style, *calculated_size, scaling_factor);
@@ -241,7 +241,7 @@ pub fn flex_node_system(
         }
     }
 
-    for (entity, style, calculated_size) in changed_size_query.iter() {
+    for (entity, style, calculated_size) in &changed_size_query {
         flex_surface.upsert_leaf(entity, style, *calculated_size, logical_to_physical_factor);
     }
 
@@ -253,7 +253,7 @@ pub fn flex_node_system(
     }
 
     // update children
-    for (entity, children) in children_query.iter() {
+    for (entity, children) in &children_query {
         flex_surface.update_children(entity, children);
     }
 
@@ -265,7 +265,7 @@ pub fn flex_node_system(
     let to_logical = |v| (physical_to_logical_factor * v as f64) as f32;
 
     // PERF: try doing this incrementally
-    for (entity, mut node, mut transform, parent) in node_transform_query.iter_mut() {
+    for (entity, mut node, mut transform, parent) in &mut node_transform_query {
         let layout = flex_surface.get_layout(entity).unwrap();
         let new_size = Vec2::new(
             to_logical(layout.size.width),

crates/bevy_ui/src/render/mod.rs

@@ -529,8 +529,8 @@ pub fn queue_uinodes(
         }));
         let draw_ui_function = draw_functions.read().get_id::<DrawUi>().unwrap();
         let pipeline = pipelines.specialize(&mut pipeline_cache, &ui_pipeline, UiPipelineKey {});
-        for mut transparent_phase in views.iter_mut() {
+        for mut transparent_phase in &mut views {
-            for (entity, batch) in ui_batches.iter() {
+            for (entity, batch) in &ui_batches {
                 image_bind_groups
                     .values
                     .entry(batch.image.clone_weak())

crates/bevy_ui/src/update.rs

@@ -23,7 +23,7 @@ pub fn ui_z_system(
     children_query: Query<&Children>,
 ) {
     let mut current_global_z = 0.0;
-    for entity in root_node_query.iter() {
+    for entity in &root_node_query {
         current_global_z = update_hierarchy(
             &children_query,
             &mut node_query,
@@ -71,7 +71,7 @@ pub fn update_clipping_system(
     mut node_query: Query<(&Node, &GlobalTransform, &Style, Option<&mut CalculatedClip>)>,
     children_query: Query<&Children>,
 ) {
-    for root_node in root_node_query.iter() {
+    for root_node in &root_node_query {
         update_clipping(
             &mut commands,
             &children_query,

crates/bevy_ui/src/widget/image.rs

@@ -25,7 +25,7 @@ pub fn image_node_system(
     textures: Res<Assets<Image>>,
     mut query: Query<(&mut CalculatedSize, &UiImage), With<ImageMode>>,
 ) {
-    for (mut calculated_size, image) in query.iter_mut() {
+    for (mut calculated_size, image) in &mut query {
         if let Some(texture) = textures.get(image) {
             let size = Size {
                 width: texture.texture_descriptor.size.width as f32,

crates/bevy_window/src/window.rs

@@ -162,7 +162,7 @@ impl WindowResizeConstraints {
 /// # App::new().add_system(access_window_system).run();
 /// # }
 /// fn access_window_system(mut windows: ResMut<Windows>){
-///     for mut window in windows.iter_mut(){
+///     for mut window in windows.iter_mut() {
 ///         window.set_title(String::from("Yay, I'm a window!"));
 ///     }
 /// }

examples/2d/mesh2d_manual.rs

@@ -317,7 +317,7 @@ pub fn queue_colored_mesh2d(
         return;
     }
     // Iterate each view (a camera is a view)
-    for (visible_entities, mut transparent_phase) in views.iter_mut() {
+    for (visible_entities, mut transparent_phase) in &mut views {
         let draw_colored_mesh2d = transparent_draw_functions
             .read()
             .get_id::<DrawColoredMesh2d>()

examples/2d/move_sprite.rs

@@ -30,7 +30,7 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
 /// The sprite is animated by changing its translation depending on the time that has passed since
 /// the last frame.
 fn sprite_movement(time: Res<Time>, mut sprite_position: Query<(&mut Direction, &mut Transform)>) {
-    for (mut logo, mut transform) in sprite_position.iter_mut() {
+    for (mut logo, mut transform) in &mut sprite_position {
         match *logo {
             Direction::Up => transform.translation.y += 150. * time.delta_seconds(),
             Direction::Down => transform.translation.y -= 150. * time.delta_seconds(),

examples/2d/rotation.rs

@@ -156,7 +156,7 @@ fn snap_to_player_system(
     // get the player translation in 2D
     let player_translation = player_transform.translation.xy();
 
-    for mut enemy_transform in query.iter_mut() {
+    for mut enemy_transform in &mut query {
         // get the vector from the enemy ship to the player ship in 2D and normalize it.
         let to_player = (player_translation - enemy_transform.translation.xy()).normalize();
 
@@ -198,7 +198,7 @@ fn rotate_to_player_system(
     // get the player translation in 2D
     let player_translation = player_transform.translation.xy();
 
-    for (config, mut enemy_transform) in query.iter_mut() {
+    for (config, mut enemy_transform) in &mut query {
         // get the enemy ship forward vector in 2D (already unit length)
         let enemy_forward = (enemy_transform.rotation * Vec3::Y).xy();
 

examples/2d/sprite_sheet.rs

@@ -24,7 +24,7 @@ fn animate_sprite(
         &Handle<TextureAtlas>,
     )>,
 ) {
-    for (mut timer, mut sprite, texture_atlas_handle) in query.iter_mut() {
+    for (mut timer, mut sprite, texture_atlas_handle) in &mut query {
         timer.tick(time.delta());
         if timer.just_finished() {
             let texture_atlas = texture_atlases.get(texture_atlas_handle).unwrap();

examples/2d/text2d.rs

@@ -100,7 +100,7 @@ fn animate_translation(
     time: Res<Time>,
     mut query: Query<&mut Transform, (With<Text>, With<AnimateTranslation>)>,
 ) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.translation.x = 100.0 * time.seconds_since_startup().sin() as f32 - 400.0;
         transform.translation.y = 100.0 * time.seconds_since_startup().cos() as f32;
     }
@@ -110,7 +110,7 @@ fn animate_rotation(
     time: Res<Time>,
     mut query: Query<&mut Transform, (With<Text>, With<AnimateRotation>)>,
 ) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotation = Quat::from_rotation_z(time.seconds_since_startup().cos() as f32);
     }
 }
@@ -121,7 +121,7 @@ fn animate_scale(
 ) {
     // Consider changing font-size instead of scaling the transform. Scaling a Text2D will scale the
     // rendered quad, resulting in a pixellated look.
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.translation = Vec3::new(400.0, 0.0, 0.0);
         transform.scale = Vec3::splat((time.seconds_since_startup().sin() as f32 + 1.1) * 2.0);
     }

examples/3d/lighting.rs

@@ -219,7 +219,7 @@ fn animate_light_direction(
     time: Res<Time>,
     mut query: Query<&mut Transform, With<DirectionalLight>>,
 ) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotate_y(time.delta_seconds() * 0.5);
     }
 }
@@ -229,7 +229,7 @@ fn movement(
     time: Res<Time>,
     mut query: Query<&mut Transform, With<Movable>>,
 ) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         let mut direction = Vec3::ZERO;
         if input.pressed(KeyCode::Up) {
             direction.y += 1.0;

examples/3d/load_gltf.rs

@@ -46,7 +46,7 @@ fn animate_light_direction(
     time: Res<Time>,
     mut query: Query<&mut Transform, With<DirectionalLight>>,
 ) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotation = Quat::from_euler(
             EulerRot::ZYX,
             0.0,

examples/3d/parenting.rs

@@ -17,7 +17,7 @@ struct Rotator;
 
 /// rotates the parent, which will result in the child also rotating
 fn rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<Rotator>>) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotate_x(3.0 * time.delta_seconds());
     }
 }

examples/3d/render_to_texture.rs

@@ -144,7 +144,7 @@ fn setup(
 
 /// Rotates the inner cube (first pass)
 fn rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<FirstPassCube>>) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotate_x(1.5 * time.delta_seconds());
         transform.rotate_z(1.3 * time.delta_seconds());
     }
@@ -152,7 +152,7 @@ fn rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<FirstPa
 
 /// Rotates the outer cube (main pass)
 fn cube_rotator_system(time: Res<Time>, mut query: Query<&mut Transform, With<MainPassCube>>) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotate_x(1.0 * time.delta_seconds());
         transform.rotate_y(0.7 * time.delta_seconds());
     }

examples/3d/shadow_biases.rs

@@ -118,7 +118,7 @@ fn toggle_light(
     mut directional_lights: Query<&mut DirectionalLight>,
 ) {
     if input.just_pressed(KeyCode::L) {
-        for mut light in point_lights.iter_mut() {
+        for mut light in &mut point_lights {
             light.intensity = if light.intensity == 0.0 {
                 println!("Using PointLight");
                 100000000.0
@@ -126,7 +126,7 @@ fn toggle_light(
                 0.0
             };
         }
-        for mut light in directional_lights.iter_mut() {
+        for mut light in &mut directional_lights {
             light.illuminance = if light.illuminance == 0.0 {
                 println!("Using DirectionalLight");
                 100000.0
@@ -140,7 +140,7 @@ fn toggle_light(
 fn adjust_point_light_biases(input: Res<Input<KeyCode>>, mut query: Query<&mut PointLight>) {
     let depth_bias_step_size = 0.01;
     let normal_bias_step_size = 0.1;
-    for mut light in query.iter_mut() {
+    for mut light in &mut query {
         if input.just_pressed(KeyCode::Key1) {
             light.shadow_depth_bias -= depth_bias_step_size;
             println!("PointLight shadow_depth_bias: {}", light.shadow_depth_bias);
@@ -172,7 +172,7 @@ fn adjust_directional_light_biases(
 ) {
     let depth_bias_step_size = 0.01;
     let normal_bias_step_size = 0.1;
-    for mut light in query.iter_mut() {
+    for mut light in &mut query {
         if input.just_pressed(KeyCode::Key5) {
             light.shadow_depth_bias -= depth_bias_step_size;
             println!(
@@ -259,7 +259,7 @@ fn camera_controller(
         mouse_delta += mouse_event.delta;
     }
 
-    for (mut transform, mut options) in query.iter_mut() {
+    for (mut transform, mut options) in &mut query {
         if !options.enabled {
             continue;
         }

examples/3d/shadow_caster_receiver.rs

@@ -124,7 +124,7 @@ fn toggle_light(
     mut directional_lights: Query<&mut DirectionalLight>,
 ) {
     if input.just_pressed(KeyCode::L) {
-        for mut light in point_lights.iter_mut() {
+        for mut light in &mut point_lights {
             light.intensity = if light.intensity == 0.0 {
                 println!("Using PointLight");
                 100000000.0
@@ -132,7 +132,7 @@ fn toggle_light(
                 0.0
             };
         }
-        for mut light in directional_lights.iter_mut() {
+        for mut light in &mut directional_lights {
             light.illuminance = if light.illuminance == 0.0 {
                 println!("Using DirectionalLight");
                 100000.0

examples/3d/shapes.rs

@@ -86,7 +86,7 @@ fn setup(
 }
 
 fn rotate(mut query: Query<&mut Transform, With<Shape>>, time: Res<Time>) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotate_y(time.delta_seconds() / 2.);
     }
 }

examples/3d/update_gltf_scene.rs

@@ -48,7 +48,7 @@ fn move_scene_entities(
     children: Query<&Children>,
     mut transforms: Query<&mut Transform>,
 ) {
-    for moved_scene_entity in moved_scene.iter() {
+    for moved_scene_entity in &moved_scene {
         let mut offset = 0.;
         iter_hierarchy(moved_scene_entity, &children, &mut |entity| {
             if let Ok(mut transform) = transforms.get_mut(entity) {

examples/animation/custom_skinned_mesh.rs

@@ -163,7 +163,7 @@ fn setup(
 
 /// Animate the joint marked with [`AnimatedJoint`] component.
 fn joint_animation(time: Res<Time>, mut query: Query<&mut Transform, With<AnimatedJoint>>) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotation = Quat::from_axis_angle(
             Vec3::Z,
             0.5 * PI * time.time_since_startup().as_secs_f32().sin(),

examples/animation/gltf_skinned_mesh.rs

@@ -50,7 +50,7 @@ fn joint_animation(
     mut transform_query: Query<&mut Transform>,
 ) {
     // Iter skinned mesh entity
-    for skinned_mesh_parent in parent_query.iter() {
+    for skinned_mesh_parent in &parent_query {
         // Mesh node is the parent of the skinned mesh entity.
         let mesh_node_entity = skinned_mesh_parent.get();
         // Get `Children` in the mesh node.

examples/async_tasks/async_compute.rs

@@ -86,7 +86,7 @@ fn handle_tasks(
     box_mesh_handle: Res<BoxMeshHandle>,
     box_material_handle: Res<BoxMaterialHandle>,
 ) {
-    for (entity, mut task) in transform_tasks.iter_mut() {
+    for (entity, mut task) in &mut transform_tasks {
         if let Some(transform) = future::block_on(future::poll_once(&mut task.0)) {
             // Add our new PbrBundle of components to our tagged entity
             commands.entity(entity).insert_bundle(PbrBundle {

examples/async_tasks/external_source_external_thread.rs

@@ -84,7 +84,7 @@ fn move_text(
     mut texts: Query<(Entity, &mut Transform), With<Text>>,
     time: Res<Time>,
 ) {
-    for (entity, mut position) in texts.iter_mut() {
+    for (entity, mut position) in &mut texts {
         position.translation -= Vec3::new(0.0, 100.0 * time.delta_seconds(), 0.0);
         if position.translation.y < -300.0 {
             commands.entity(entity).despawn();

examples/ecs/component_change_detection.rs

@@ -22,7 +22,7 @@ fn setup(mut commands: Commands) {
 }
 
 fn change_component(time: Res<Time>, mut query: Query<(Entity, &mut MyComponent)>) {
-    for (entity, mut component) in query.iter_mut() {
+    for (entity, mut component) in &mut query {
         if rand::thread_rng().gen_bool(0.1) {
             info!("changing component {:?}", entity);
             component.0 = time.seconds_since_startup();
@@ -33,7 +33,7 @@ fn change_component(time: Res<Time>, mut query: Query<(Entity, &mut MyComponent)
 // There are query filters for `Changed<T>` and `Added<T>`
 // Only entities matching the filters will be in the query
 fn change_detection(query: Query<(Entity, &MyComponent), Changed<MyComponent>>) {
-    for (entity, component) in query.iter() {
+    for (entity, component) in &query {
         info!("{:?} changed: {:?}", entity, component,);
     }
 }
@@ -46,7 +46,7 @@ fn tracker_monitoring(
         Option<ChangeTrackers<MyComponent>>,
     )>,
 ) {
-    for (entity, component, trackers) in query.iter() {
+    for (entity, component, trackers) in &query {
         info!("{:?}: {:?} -> {:?}", entity, component, trackers);
     }
 }

examples/ecs/custom_query_param.rs

@@ -56,7 +56,7 @@ fn print_components_read_only(
     query: Query<ReadOnlyCustomQuery<ComponentC, ComponentD>, QueryFilter<ComponentC, ComponentD>>,
 ) {
     println!("Print components (read_only):");
-    for e in query.iter() {
+    for e in &query {
         println!("Entity: {:?}", e.entity);
         println!("A: {:?}", e.a);
         println!("B: {:?}", e.b);
@@ -127,7 +127,7 @@ fn print_components_iter_mut(
     mut query: Query<CustomQuery<ComponentC, ComponentD>, QueryFilter<ComponentC, ComponentD>>,
 ) {
     println!("Print components (iter_mut):");
-    for e in query.iter_mut() {
+    for e in &mut query {
         // Re-declaring the variable to illustrate the type of the actual iterator item.
         let e: CustomQueryItem<'_, _, _> = e;
         println!("Entity: {:?}", e.entity);
@@ -145,7 +145,7 @@ fn print_components_iter(
     query: Query<CustomQuery<ComponentC, ComponentD>, QueryFilter<ComponentC, ComponentD>>,
 ) {
     println!("Print components (iter):");
-    for e in query.iter() {
+    for e in &query {
         // Re-declaring the variable to illustrate the type of the actual iterator item.
         let e: CustomQueryReadOnlyItem<'_, _, _> = e;
         println!("Entity: {:?}", e.entity);
@@ -177,7 +177,7 @@ fn print_components_tuple(
     >,
 ) {
     println!("Print components (tuple):");
-    for (entity, a, b, nested, (generic_c, generic_d)) in query.iter() {
+    for (entity, a, b, nested, (generic_c, generic_d)) in &query {
         println!("Entity: {:?}", entity);
         println!("A: {:?}", a);
         println!("B: {:?}", b);

examples/ecs/ecs_guide.rs

@@ -88,7 +88,7 @@ fn new_round_system(game_rules: Res<GameRules>, mut game_state: ResMut<GameState
 
 // This system updates the score for each entity with the "Player" and "Score" component.
 fn score_system(mut query: Query<(&Player, &mut Score)>) {
-    for (player, mut score) in query.iter_mut() {
+    for (player, mut score) in &mut query {
         let scored_a_point = random::<bool>();
         if scored_a_point {
             score.value += 1;
@@ -114,7 +114,7 @@ fn score_check_system(
     mut game_state: ResMut<GameState>,
     query: Query<(&Player, &Score)>,
 ) {
-    for (player, score) in query.iter() {
+    for (player, score) in &query {
         if score.value == game_rules.winning_score {
             game_state.winning_player = Some(player.name.clone());
         }

examples/ecs/generic_system.rs

@@ -66,7 +66,7 @@ fn setup_system(mut commands: Commands) {
 }
 
 fn print_text_system(time: Res<Time>, mut query: Query<(&mut PrinterTick, &TextToPrint)>) {
-    for (mut timer, text) in query.iter_mut() {
+    for (mut timer, text) in &mut query {
         if timer.tick(time.delta()).just_finished() {
             info!("{}", text.0);
         }
@@ -85,7 +85,7 @@ fn transition_to_in_game_system(
 // Type arguments on functions come after the function name, but before ordinary arguments.
 // Here, the `Component` trait is a trait bound on T, our generic type
 fn cleanup_system<T: Component>(mut commands: Commands, query: Query<Entity, With<T>>) {
-    for e in query.iter() {
+    for e in &query {
         commands.entity(e).despawn_recursive();
     }
 }

examples/ecs/hierarchy.rs

@@ -71,14 +71,14 @@ fn rotate(
     mut transform_query: Query<&mut Transform, With<Sprite>>,
 ) {
     let angle = std::f32::consts::PI / 2.0;
-    for (parent, children) in parents_query.iter_mut() {
+    for (parent, children) in &mut parents_query {
         if let Ok(mut transform) = transform_query.get_mut(parent) {
             transform.rotate_z(-angle * time.delta_seconds());
         }
 
         // To iterate through the entities children, just treat the Children component as a Vec
         // Alternatively, you could query entities that have a Parent component
-        for child in children.iter() {
+        for child in children {
             if let Ok(mut transform) = transform_query.get_mut(*child) {
                 transform.rotate_z(angle * 2.0 * time.delta_seconds());
             }

examples/ecs/iter_combinations.rs

@@ -164,7 +164,7 @@ fn interact_bodies(mut query: Query<(&Mass, &GlobalTransform, &mut Acceleration)
 
 fn integrate(mut query: Query<(&mut Acceleration, &mut Transform, &mut LastPos)>) {
     let dt_sq = (DELTA_TIME * DELTA_TIME) as f32;
-    for (mut acceleration, mut transform, mut last_pos) in query.iter_mut() {
+    for (mut acceleration, mut transform, mut last_pos) in &mut query {
         // verlet integration
         // x(t+dt) = 2x(t) - x(t-dt) + a(t)dt^2 + O(dt^4)
 

examples/ecs/state.rs

@@ -79,7 +79,7 @@ fn menu(
         (Changed<Interaction>, With<Button>),
     >,
 ) {
-    for (interaction, mut color) in interaction_query.iter_mut() {
+    for (interaction, mut color) in &mut interaction_query {
         match *interaction {
             Interaction::Clicked => {
                 *color = PRESSED_BUTTON.into();
@@ -112,7 +112,7 @@ fn movement(
     input: Res<Input<KeyCode>>,
     mut query: Query<&mut Transform, With<Sprite>>,
 ) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         let mut direction = Vec3::ZERO;
         if input.pressed(KeyCode::Left) {
             direction.x -= 1.0;
@@ -134,7 +134,7 @@ fn movement(
 }
 
 fn change_color(time: Res<Time>, mut query: Query<&mut Sprite>) {
-    for mut sprite in query.iter_mut() {
+    for mut sprite in &mut query {
         sprite
             .color
             .set_b((time.seconds_since_startup() * 0.5).sin() as f32 + 2.0);

examples/ecs/timers.rs

@@ -45,7 +45,7 @@ fn setup(mut commands: Commands) {
 /// This system ticks all the `Timer` components on entities within the scene
 /// using bevy's `Time` resource to get the delta between each update.
 fn print_when_completed(time: Res<Time>, mut query: Query<&mut PrintOnCompletionTimer>) {
-    for mut timer in query.iter_mut() {
+    for mut timer in &mut query {
         if timer.tick(time.delta()).just_finished() {
             info!("Entity timer just finished");
         }

examples/games/alien_cake_addict.rs

@@ -175,7 +175,7 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>, mut game: ResMu
 
 // remove all entities that are not a camera
 fn teardown(mut commands: Commands, entities: Query<Entity, Without<Camera>>) {
-    for entity in entities.iter() {
+    for entity in &entities {
         commands.entity(entity).despawn_recursive();
     }
 }

examples/games/breakout.rs

@@ -343,7 +343,7 @@ fn move_paddle(
 }
 
 fn apply_velocity(mut query: Query<(&mut Transform, &Velocity)>) {
-    for (mut transform, velocity) in query.iter_mut() {
+    for (mut transform, velocity) in &mut query {
         transform.translation.x += velocity.x * TIME_STEP;
         transform.translation.y += velocity.y * TIME_STEP;
     }
@@ -365,7 +365,7 @@ fn check_for_collisions(
     let ball_size = ball_transform.scale.truncate();
 
     // check collision with walls
-    for (collider_entity, transform, maybe_brick) in collider_query.iter() {
+    for (collider_entity, transform, maybe_brick) in &collider_query {
         let collision = collide(
             ball_transform.translation,
             ball_size,

examples/games/contributors.rs

@@ -242,7 +242,7 @@ fn deselect(sprite: &mut Sprite, contributor: &Contributor, transform: &mut Tran
 fn velocity_system(time: Res<Time>, mut velocity_query: Query<&mut Velocity>) {
     let delta = time.delta_seconds();
 
-    for mut velocity in velocity_query.iter_mut() {
+    for mut velocity in &mut velocity_query {
         velocity.translation += Vec3::new(0.0, GRAVITY * delta, 0.0);
     }
 }
@@ -266,7 +266,7 @@ fn collision_system(
     let wall_left = -(window.width() / 2.);
     let wall_right = window.width() / 2.;
 
-    for (mut velocity, mut transform) in query.iter_mut() {
+    for (mut velocity, mut transform) in &mut query {
         let left = transform.translation.x - SPRITE_SIZE / 2.0;
         let right = transform.translation.x + SPRITE_SIZE / 2.0;
         let top = transform.translation.y + SPRITE_SIZE / 2.0;
@@ -299,7 +299,7 @@ fn collision_system(
 fn move_system(time: Res<Time>, mut query: Query<(&Velocity, &mut Transform)>) {
     let delta = time.delta_seconds();
 
-    for (velocity, mut transform) in query.iter_mut() {
+    for (velocity, mut transform) in &mut query {
         transform.translation += delta * velocity.translation;
         transform.rotate_z(velocity.rotation * delta);
     }

examples/games/game_menu.rs

@@ -356,7 +356,7 @@ mod menu {
             (Changed<Interaction>, With<Button>),
         >,
     ) {
-        for (interaction, mut color, selected) in interaction_query.iter_mut() {
+        for (interaction, mut color, selected) in &mut interaction_query {
             *color = match (*interaction, selected) {
                 (Interaction::Clicked, _) | (Interaction::None, Some(_)) => PRESSED_BUTTON.into(),
                 (Interaction::Hovered, Some(_)) => HOVERED_PRESSED_BUTTON.into(),
@@ -374,7 +374,7 @@ mod menu {
         mut commands: Commands,
         mut setting: ResMut<T>,
     ) {
-        for (interaction, button_setting, entity) in interaction_query.iter() {
+        for (interaction, button_setting, entity) in &interaction_query {
             if *interaction == Interaction::Clicked && *setting != *button_setting {
                 let (previous_button, mut previous_color) = selected_query.single_mut();
                 *previous_color = NORMAL_BUTTON.into();
@@ -787,7 +787,7 @@ mod menu {
         mut menu_state: ResMut<State<MenuState>>,
         mut game_state: ResMut<State<GameState>>,
     ) {
-        for (interaction, menu_button_action) in interaction_query.iter() {
+        for (interaction, menu_button_action) in &interaction_query {
             if *interaction == Interaction::Clicked {
                 match menu_button_action {
                     MenuButtonAction::Quit => app_exit_events.send(AppExit),
@@ -814,7 +814,7 @@ mod menu {
 
 // Generic system that takes a component as a parameter, and will despawn all entities with that component
 fn despawn_screen<T: Component>(to_despawn: Query<Entity, With<T>>, mut commands: Commands) {
-    for entity in to_despawn.iter() {
+    for entity in &to_despawn {
         commands.entity(entity).despawn_recursive();
     }
 }

examples/ios/src/lib.rs

@@ -134,7 +134,7 @@ fn button_handler(
         (Changed<Interaction>, With<Button>),
     >,
 ) {
-    for (interaction, mut color) in interaction_query.iter_mut() {
+    for (interaction, mut color) in &mut interaction_query {
         match *interaction {
             Interaction::Clicked => {
                 *color = Color::BLUE.into();

examples/scene/scene.rs

@@ -66,7 +66,7 @@ fn load_scene_system(mut commands: Commands, asset_server: Res<AssetServer>) {
 // This system logs all ComponentA components in our world. Try making a change to a ComponentA in
 // load_scene_example.scn. You should immediately see the changes appear in the console.
 fn log_system(query: Query<(Entity, &ComponentA), Changed<ComponentA>>) {
-    for (entity, component_a) in query.iter() {
+    for (entity, component_a) in &query {
         info!("  Entity({})", entity.id());
         info!(
             "    ComponentA: {{ x: {} y: {} }}\n",

examples/shader/animate_shader.rs

@@ -116,9 +116,9 @@ fn queue_custom(
     let key = MeshPipelineKey::from_msaa_samples(msaa.samples)
         | MeshPipelineKey::from_primitive_topology(PrimitiveTopology::TriangleList);
 
-    for (view, mut transparent_phase) in views.iter_mut() {
+    for (view, mut transparent_phase) in &mut views {
         let rangefinder = view.rangefinder3d();
-        for (entity, mesh_uniform, mesh_handle) in material_meshes.iter() {
+        for (entity, mesh_uniform, mesh_handle) in &material_meshes {
             if let Some(mesh) = render_meshes.get(mesh_handle) {
                 let pipeline = pipelines
                     .specialize(&mut pipeline_cache, &custom_pipeline, key, &mesh.layout)

examples/shader/post_processing.rs

@@ -157,7 +157,7 @@ fn main_camera_cube_rotator_system(
     time: Res<Time>,
     mut query: Query<&mut Transform, With<MainCube>>,
 ) {
-    for mut transform in query.iter_mut() {
+    for mut transform in &mut query {
         transform.rotate_x(0.55 * time.delta_seconds());
         transform.rotate_z(0.15 * time.delta_seconds());
     }

examples/shader/shader_instancing.rs

@@ -116,9 +116,9 @@ fn queue_custom(
 
     let msaa_key = MeshPipelineKey::from_msaa_samples(msaa.samples);
 
-    for (view, mut transparent_phase) in views.iter_mut() {
+    for (view, mut transparent_phase) in &mut views {
         let rangefinder = view.rangefinder3d();
-        for (entity, mesh_uniform, mesh_handle) in material_meshes.iter() {
+        for (entity, mesh_uniform, mesh_handle) in &material_meshes {
             if let Some(mesh) = meshes.get(mesh_handle) {
                 let key =
                     msaa_key | MeshPipelineKey::from_primitive_topology(mesh.primitive_topology);
@@ -147,7 +147,7 @@ fn prepare_instance_buffers(
     query: Query<(Entity, &InstanceMaterialData)>,
     render_device: Res<RenderDevice>,
 ) {
-    for (entity, instance_data) in query.iter() {
+    for (entity, instance_data) in &query {
         let buffer = render_device.create_buffer_with_data(&BufferInitDescriptor {
             label: Some("instance data buffer"),
             contents: bytemuck::cast_slice(instance_data.as_slice()),

examples/stress_tests/bevymark.rs

@@ -223,7 +223,7 @@ fn spawn_birds(
 }
 
 fn movement_system(time: Res<Time>, mut bird_query: Query<(&mut Bird, &mut Transform)>) {
-    for (mut bird, mut transform) in bird_query.iter_mut() {
+    for (mut bird, mut transform) in &mut bird_query {
         transform.translation.x += bird.velocity.x * time.delta_seconds();
         transform.translation.y += bird.velocity.y * time.delta_seconds();
         bird.velocity.y += GRAVITY * time.delta_seconds();
@@ -235,7 +235,7 @@ fn collision_system(windows: Res<Windows>, mut bird_query: Query<(&mut Bird, &Tr
     let half_width = window.width() as f32 * 0.5;
     let half_height = window.height() as f32 * 0.5;
 
-    for (mut bird, transform) in bird_query.iter_mut() {
+    for (mut bird, transform) in &mut bird_query {
         let x_vel = bird.velocity.x;
         let y_vel = bird.velocity.y;
         let x_pos = transform.translation.x;

examples/stress_tests/many_foxes.rs

@@ -187,7 +187,7 @@ fn setup_scene_once_loaded(
     mut done: Local<bool>,
 ) {
     if !*done && player.iter().len() == foxes.count {
-        for mut player in player.iter_mut() {
+        for mut player in &mut player {
             player.play(animations.0[0].clone_weak()).repeat();
         }
         *done = true;
@@ -204,7 +204,7 @@ fn update_fox_rings(
     }
 
     let dt = time.delta_seconds();
-    for (ring, rotation_direction, mut transform) in rings.iter_mut() {
+    for (ring, rotation_direction, mut transform) in &mut rings {
         let angular_velocity = foxes.speed / ring.radius;
         transform.rotate_y(rotation_direction.sign() * angular_velocity * dt);
     }
@@ -233,7 +233,7 @@ fn keyboard_animation_control(
         *current_animation = (*current_animation + 1) % animations.0.len();
     }
 
-    for mut player in animation_player.iter_mut() {
+    for mut player in &mut animation_player {
         if keyboard_input.just_pressed(KeyCode::Space) {
             if player.is_paused() {
                 player.resume();

examples/stress_tests/transform_hierarchy.rs

@@ -244,7 +244,7 @@ struct Update(f32);
 
 /// update positions system
 fn update(time: Res<Time>, mut query: Query<(&mut Transform, &mut Update)>) {
-    for (mut t, mut u) in query.iter_mut() {
+    for (mut t, mut u) in &mut query {
         u.0 += time.delta_seconds() * 0.1;
         set_translation(&mut t.translation, u.0);
     }

examples/tools/scene_viewer.rs

@@ -219,7 +219,7 @@ fn setup_scene_after_load(
 
         let mut min = Vec3A::splat(f32::MAX);
         let mut max = Vec3A::splat(f32::MIN);
-        for (transform, maybe_aabb) in meshes.iter() {
+        for (transform, maybe_aabb) in &meshes {
             let aabb = maybe_aabb.unwrap();
             // If the Aabb had not been rotated, applying the non-uniform scale would produce the
             // correct bounds. However, it could very well be rotated and so we first convert to
@@ -309,7 +309,7 @@ fn update_lights(
     } else if key_input.just_pressed(KeyCode::Key0) {
         projection_adjustment.z += SCALE_STEP;
     }
-    for (_, mut light) in query.iter_mut() {
+    for (_, mut light) in &mut query {
         light.shadow_projection.left *= projection_adjustment.x;
         light.shadow_projection.right *= projection_adjustment.x;
         light.shadow_projection.bottom *= projection_adjustment.y;
@@ -325,7 +325,7 @@ fn update_lights(
         *animate_directional_light = !*animate_directional_light;
     }
     if *animate_directional_light {
-        for (mut transform, _) in query.iter_mut() {
+        for (mut transform, _) in &mut query {
             transform.rotation = Quat::from_euler(
                 EulerRot::ZYX,
                 0.0,

examples/transforms/3d_rotation.rs

@@ -48,7 +48,7 @@ fn setup(
 
 // This system will rotate any entity in the scene with a Rotatable component around its y-axis.
 fn rotate_cube(mut cubes: Query<(&mut Transform, &Rotatable)>, timer: Res<Time>) {
-    for (mut transform, cube) in cubes.iter_mut() {
+    for (mut transform, cube) in &mut cubes {
         // The speed is first multiplied by TAU which is a full rotation (360deg) in radians,
         // and then multiplied by delta_seconds which is the time that passed last frame.
         // In other words. Speed is equal to the amount of rotations per second.

examples/transforms/global_vs_local_translation.rs

@@ -128,7 +128,7 @@ fn move_cubes_according_to_global_transform(
     direction: Res<Direction>,
     timer: Res<Time>,
 ) {
-    for mut global_transform in cubes.iter_mut() {
+    for mut global_transform in &mut cubes {
         global_transform.translation += direction.0 * timer.delta_seconds();
     }
 }
@@ -139,7 +139,7 @@ fn move_cubes_according_to_local_transform(
     direction: Res<Direction>,
     timer: Res<Time>,
 ) {
-    for mut transform in cubes.iter_mut() {
+    for mut transform in &mut cubes {
         transform.translation += direction.0 * timer.delta_seconds();
     }
 }
@@ -166,7 +166,7 @@ fn toggle_movement(
 ) {
     // Update the currently movable entities and remove their Move component if the assigned key was pressed to disable their movement.
     // This will also make them transparent so they can be identified as 'disabled' in the scene.
-    for (entity, material_handle, toggled_by) in movable_entities.iter() {
+    for (entity, material_handle, toggled_by) in &movable_entities {
         if keyboard_input.just_pressed(toggled_by.0) {
             materials
                 .get_mut(material_handle)
@@ -178,7 +178,7 @@ fn toggle_movement(
     }
     // Update the currently non-movable entities and add a Move component if the assigned key was pressed to enable their movement.
     // This will also make them opaque so they can be identified as 'enabled' in the scene.
-    for (entity, material_handle, toggled_by) in static_entities.iter() {
+    for (entity, material_handle, toggled_by) in &static_entities {
         if keyboard_input.just_pressed(toggled_by.0) {
             materials
                 .get_mut(material_handle)

examples/transforms/scale.rs

@@ -66,7 +66,7 @@ fn setup(
 // This system will check if a scaled entity went above or below the entities scaling bounds
 // and change the direction of the scaling vector.
 fn change_scale_direction(mut cubes: Query<(&mut Transform, &mut Scaling)>) {
-    for (mut transform, mut cube) in cubes.iter_mut() {
+    for (mut transform, mut cube) in &mut cubes {
         // If an entity scaled beyond the maximum of its size in any dimension
         // the scaling vector is flipped so the scaling is gradually reverted.
         // Additionally, to ensure the condition does not trigger again we floor the elements to
@@ -92,7 +92,7 @@ fn change_scale_direction(mut cubes: Query<(&mut Transform, &mut Scaling)>) {
 // This system will scale any entity with assigned Scaling in each direction
 // by cycling through the directions to scale.
 fn scale_cube(mut cubes: Query<(&mut Transform, &Scaling)>, timer: Res<Time>) {
-    for (mut transform, cube) in cubes.iter_mut() {
+    for (mut transform, cube) in &mut cubes {
         transform.scale += cube.scale_direction * cube.scale_speed * timer.delta_seconds();
     }
 }

examples/transforms/transform.rs

@@ -90,7 +90,7 @@ fn setup(
 
 // This system will move the cube forward.
 fn move_cube(mut cubes: Query<(&mut Transform, &mut CubeState)>, timer: Res<Time>) {
-    for (mut transform, cube) in cubes.iter_mut() {
+    for (mut transform, cube) in &mut cubes {
         // Move the cube forward smoothly at a given move_speed.
         let forward = transform.forward();
         transform.translation += forward * cube.move_speed * timer.delta_seconds();
@@ -107,11 +107,11 @@ fn rotate_cube(
 ) {
     // Calculate the point to circle around. (The position of the center_sphere)
     let mut center: Vec3 = Vec3::ZERO;
-    for sphere in center_spheres.iter() {
+    for sphere in &center_spheres {
         center += sphere.translation;
     }
     // Update the rotation of the cube(s).
-    for (mut transform, cube) in cubes.iter_mut() {
+    for (mut transform, cube) in &mut cubes {
         // Calculate the rotation of the cube if it would be looking at the sphere in the center.
         let look_at_sphere = transform.looking_at(center, transform.local_y());
         // Interpolate between the current rotation and the fully turned rotation
@@ -132,11 +132,11 @@ fn scale_down_sphere_proportional_to_cube_travel_distance(
     // First we need to calculate the length of between
     // the current position of the orbiting cube and the spawn position.
     let mut distances = 0.0;
-    for (cube_transform, cube_state) in cubes.iter() {
+    for (cube_transform, cube_state) in &cubes {
         distances += (cube_state.start_pos - cube_transform.translation).length();
     }
     // Now we use the calculated value to scale the sphere in the center accordingly.
-    for (mut transform, center) in centers.iter_mut() {
+    for (mut transform, center) in &mut centers {
         // Calculate the new size from the calculated distances and the centers scale_factor.
         // Since we want to have the sphere at its max_size at the cubes spawn location we start by
         // using the max_size as start value and subtract the distances scaled by a scaling factor.

examples/transforms/translation.rs

@@ -62,7 +62,7 @@ fn setup(
 
 // This system will move all Movable entities with a Transform
 fn move_cube(mut cubes: Query<(&mut Transform, &mut Movable)>, timer: Res<Time>) {
-    for (mut transform, mut cube) in cubes.iter_mut() {
+    for (mut transform, mut cube) in &mut cubes {
         // Check if the entity moved too far from its spawn, if so invert the moving direction.
         if (cube.spawn - transform.translation).length() > cube.max_distance {
             cube.speed *= -1.0;

examples/ui/button.rs

@@ -24,7 +24,7 @@ fn button_system(
     >,
     mut text_query: Query<&mut Text>,
 ) {
-    for (interaction, mut color, children) in interaction_query.iter_mut() {
+    for (interaction, mut color, children) in &mut interaction_query {
         let mut text = text_query.get_mut(children[0]).unwrap();
         match *interaction {
             Interaction::Clicked => {

examples/ui/font_atlas_debug.rs

@@ -65,7 +65,7 @@ fn atlas_render_system(
 
 fn text_update_system(mut state: ResMut<State>, time: Res<Time>, mut query: Query<&mut Text>) {
     if state.timer.tick(time.delta()).finished() {
-        for mut text in query.iter_mut() {
+        for mut text in &mut query {
             let c = rand::random::<u8>() as char;
             if !text.sections[0].value.contains(c) {
                 text.sections[0].value.push(c);

examples/ui/text.rs

@@ -96,7 +96,7 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
 }
 
 fn text_update_system(diagnostics: Res<Diagnostics>, mut query: Query<&mut Text, With<FpsText>>) {
-    for mut text in query.iter_mut() {
+    for mut text in &mut query {
         if let Some(fps) = diagnostics.get(FrameTimeDiagnosticsPlugin::FPS) {
             if let Some(average) = fps.average() {
                 // Update the value of the second section
@@ -107,7 +107,7 @@ fn text_update_system(diagnostics: Res<Diagnostics>, mut query: Query<&mut Text,
 }
 
 fn text_color_system(time: Res<Time>, mut query: Query<&mut Text, With<ColorText>>) {
-    for mut text in query.iter_mut() {
+    for mut text in &mut query {
         let seconds = time.seconds_since_startup() as f32;
         // We used the `Text::with_section` helper method, but it is still just a `Text`,
         // so to update it, we are still updating the one and only section

examples/ui/text_debug.rs

@@ -177,7 +177,7 @@ fn change_text_system(
     diagnostics: Res<Diagnostics>,
     mut query: Query<&mut Text, With<TextChanges>>,
 ) {
-    for mut text in query.iter_mut() {
+    for mut text in &mut query {
         let mut fps = 0.0;
         if let Some(fps_diagnostic) = diagnostics.get(FrameTimeDiagnosticsPlugin::FPS) {
             if let Some(fps_avg) = fps_diagnostic.average() {

examples/ui/ui.rs

@@ -315,7 +315,7 @@ fn mouse_scroll(
     query_item: Query<&Node>,
 ) {
     for mouse_wheel_event in mouse_wheel_events.iter() {
-        for (mut scrolling_list, mut style, children, uinode) in query_list.iter_mut() {
+        for (mut scrolling_list, mut style, children, uinode) in &mut query_list {
             let items_height: f32 = children
                 .iter()
                 .map(|entity| query_item.get(*entity).unwrap().size.y)

examples/window/low_power.rs

@@ -111,7 +111,7 @@ pub(crate) mod test_setup {
         time: Res<Time>,
         mut cube_transform: Query<&mut Transform, With<Rotator>>,
     ) {
-        for mut transform in cube_transform.iter_mut() {
+        for mut transform in &mut cube_transform {
             transform.rotate_x(time.delta_seconds());
             transform.rotate_local_y(time.delta_seconds());
         }

tests/how_to_test_systems.rs

@@ -21,7 +21,7 @@ fn despawn_dead_enemies(
     mut dead_enemies: EventWriter<EnemyDied>,
     enemies: Query<(Entity, &Enemy)>,
 ) {
-    for (entity, enemy) in enemies.iter() {
+    for (entity, enemy) in &enemies {
         if enemy.hit_points == 0 {
             commands.entity(entity).despawn_recursive();
             dead_enemies.send(EnemyDied(enemy.score_value));
@@ -30,7 +30,7 @@ fn despawn_dead_enemies(
 }
 
 fn hurt_enemies(mut enemies: Query<&mut Enemy>) {
-    for mut enemy in enemies.iter_mut() {
+    for mut enemy in &mut enemies {
         enemy.hit_points -= 1;
     }
 }