From 463b7f3afd567ee8f0cddce595ba7609955d9012 Mon Sep 17 00:00:00 2001
From: Brandon Janson <bjanson28@gmail.com>
Date: Wed, 11 Aug 2021 21:20:19 +1000
Subject: [PATCH 1/9] Add generic systems example

---
 Cargo.toml                     |  4 ++
 examples/ecs/generic_system.rs | 78 ++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 examples/ecs/generic_system.rs

diff --git a/Cargo.toml b/Cargo.toml
index 0fafd91be7970..052170c8cf083 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -274,6 +274,10 @@ path = "examples/ecs/event.rs"
 name = "fixed_timestep"
 path = "examples/ecs/fixed_timestep.rs"
 
+[[example]]
+name = "generic_system"
+path = "examples/ecs/generic_system.rs"
+
 [[example]]
 name = "hierarchy"
 path = "examples/ecs/hierarchy.rs"
diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
new file mode 100644
index 0000000000000..ab62b763657e6
--- /dev/null
+++ b/examples/ecs/generic_system.rs
@@ -0,0 +1,78 @@
+use bevy::{ecs::component::Component, prelude::*};
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash)]
+enum AppState {
+    MainMenu,
+    InGame,
+}
+
+struct TextToPrint(String);
+
+struct MenuClose;
+struct LevelUnload;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_state(AppState::MainMenu)
+        .add_startup_system(setup)
+        .add_system(print_text)
+        // .add_system(transition_to_in_game)
+        .add_system_set(
+            SystemSet::on_update(AppState::MainMenu)
+            .with_system(transition_to_in_game)
+        )
+        // add the cleanup systems
+        .add_system_set(
+            SystemSet::on_exit(AppState::MainMenu)
+            .with_system(cleanup_system::<MenuClose>)
+        )
+        .add_system_set(
+            SystemSet::on_exit(AppState::InGame)
+            .with_system(cleanup_system::<LevelUnload>)
+        )
+        .run();
+}
+
+fn setup(
+    mut commands: Commands
+) {
+    commands.spawn()
+        .insert(Timer::from_seconds(1.0, true))
+        .insert(TextToPrint("I will print until you press space.".to_string()))
+        .insert(MenuClose);
+
+    commands.spawn()
+        .insert(Timer::from_seconds(1.0, true))
+        .insert(TextToPrint("I will always print".to_string()))
+        .insert(LevelUnload);
+}
+
+fn print_text(
+    time: Res<Time>,
+    mut query: Query<(&mut Timer, &TextToPrint)>
+) {
+    for (mut timer, text) in query.iter_mut() {
+        if timer.tick(time.delta()).just_finished() {
+            info!("{}", text.0);
+        }
+    }
+}
+
+fn transition_to_in_game(
+    mut state: ResMut<State<AppState>>,
+    keyboard_input: Res<Input<KeyCode>>
+) {
+    if keyboard_input.pressed(KeyCode::Space) {
+        state.set(AppState::InGame).unwrap();
+    }
+}
+
+fn cleanup_system<T: Component>(
+    mut commands: Commands,
+    query: Query<Entity, With<T>>
+) {
+    for e in query.iter() {
+        commands.entity(e).despawn_recursive();
+    }
+}

From 2fa50b255fd1847ba8eeaa97d94b13a7aca49bba Mon Sep 17 00:00:00 2001
From: Brandon Janson <bjanson28@gmail.com>
Date: Wed, 11 Aug 2021 21:26:11 +1000
Subject: [PATCH 2/9] Fix CI issues

---
 examples/README.md             |  1 +
 examples/ecs/generic_system.rs | 41 ++++++++++++----------------------
 2 files changed, 15 insertions(+), 27 deletions(-)

diff --git a/examples/README.md b/examples/README.md
index 7796afdb16223..36e5bbf0b5b1c 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -159,6 +159,7 @@ Example | File | Description
 `component_change_detection` | [`ecs/component_change_detection.rs`](./ecs/component_change_detection.rs) | Change detection on components
 `event` | [`ecs/event.rs`](./ecs/event.rs) | Illustrates event creation, activation, and reception
 `fixed_timestep` | [`ecs/fixed_timestep.rs`](./ecs/fixed_timestep.rs) | Shows how to create systems that run every fixed timestep, rather than every tick
+`generic_system` | [`ecs/generic_system.rs`](./ecs/generic_system.rs) | Shows how to create generic systems
 `hierarchy` | [`ecs/hierarchy.rs`](./ecs/hierarchy.rs) | Creates a hierarchy of parents and children entities
 `iter_combinations` | [`ecs/iter_combinations.rs`](./ecs/iter_combinations.rs) | Shows how to iterate over combinations of query results.
 `parallel_query` | [`ecs/parallel_query.rs`](./ecs/parallel_query.rs) | Illustrates parallel queries with `ParallelIterator`
diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
index ab62b763657e6..eb513868d1896 100644
--- a/examples/ecs/generic_system.rs
+++ b/examples/ecs/generic_system.rs
@@ -17,41 +17,34 @@ fn main() {
         .add_state(AppState::MainMenu)
         .add_startup_system(setup)
         .add_system(print_text)
-        // .add_system(transition_to_in_game)
-        .add_system_set(
-            SystemSet::on_update(AppState::MainMenu)
-            .with_system(transition_to_in_game)
-        )
+        .add_system_set(SystemSet::on_update(AppState::MainMenu).with_system(transition_to_in_game))
         // add the cleanup systems
         .add_system_set(
-            SystemSet::on_exit(AppState::MainMenu)
-            .with_system(cleanup_system::<MenuClose>)
+            SystemSet::on_exit(AppState::MainMenu).with_system(cleanup_system::<MenuClose>),
         )
         .add_system_set(
-            SystemSet::on_exit(AppState::InGame)
-            .with_system(cleanup_system::<LevelUnload>)
+            SystemSet::on_exit(AppState::InGame).with_system(cleanup_system::<LevelUnload>),
         )
         .run();
 }
 
-fn setup(
-    mut commands: Commands
-) {
-    commands.spawn()
+fn setup(mut commands: Commands) {
+    commands
+        .spawn()
         .insert(Timer::from_seconds(1.0, true))
-        .insert(TextToPrint("I will print until you press space.".to_string()))
+        .insert(TextToPrint(
+            "I will print until you press space.".to_string(),
+        ))
         .insert(MenuClose);
 
-    commands.spawn()
+    commands
+        .spawn()
         .insert(Timer::from_seconds(1.0, true))
         .insert(TextToPrint("I will always print".to_string()))
         .insert(LevelUnload);
 }
 
-fn print_text(
-    time: Res<Time>,
-    mut query: Query<(&mut Timer, &TextToPrint)>
-) {
+fn print_text(time: Res<Time>, mut query: Query<(&mut Timer, &TextToPrint)>) {
     for (mut timer, text) in query.iter_mut() {
         if timer.tick(time.delta()).just_finished() {
             info!("{}", text.0);
@@ -59,19 +52,13 @@ fn print_text(
     }
 }
 
-fn transition_to_in_game(
-    mut state: ResMut<State<AppState>>,
-    keyboard_input: Res<Input<KeyCode>>
-) {
+fn transition_to_in_game(mut state: ResMut<State<AppState>>, keyboard_input: Res<Input<KeyCode>>) {
     if keyboard_input.pressed(KeyCode::Space) {
         state.set(AppState::InGame).unwrap();
     }
 }
 
-fn cleanup_system<T: Component>(
-    mut commands: Commands,
-    query: Query<Entity, With<T>>
-) {
+fn cleanup_system<T: Component>(mut commands: Commands, query: Query<Entity, With<T>>) {
     for e in query.iter() {
         commands.entity(e).despawn_recursive();
     }

From cd63208ba3b2cab90f28fdd8c5e3eab58726583b Mon Sep 17 00:00:00 2001
From: B-Janson <brandon@canva.com>
Date: Mon, 13 Sep 2021 21:28:11 +1000
Subject: [PATCH 3/9] Apply suggestions from code review

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
---
 examples/README.md             | 2 +-
 examples/ecs/generic_system.rs | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/examples/README.md b/examples/README.md
index 36e5bbf0b5b1c..7174cd953e410 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -159,7 +159,7 @@ Example | File | Description
 `component_change_detection` | [`ecs/component_change_detection.rs`](./ecs/component_change_detection.rs) | Change detection on components
 `event` | [`ecs/event.rs`](./ecs/event.rs) | Illustrates event creation, activation, and reception
 `fixed_timestep` | [`ecs/fixed_timestep.rs`](./ecs/fixed_timestep.rs) | Shows how to create systems that run every fixed timestep, rather than every tick
-`generic_system` | [`ecs/generic_system.rs`](./ecs/generic_system.rs) | Shows how to create generic systems
+`generic_system` | [`ecs/generic_system.rs`](./ecs/generic_system.rs) | Shows how to create systems that can be reused with different types
 `hierarchy` | [`ecs/hierarchy.rs`](./ecs/hierarchy.rs) | Creates a hierarchy of parents and children entities
 `iter_combinations` | [`ecs/iter_combinations.rs`](./ecs/iter_combinations.rs) | Shows how to iterate over combinations of query results.
 `parallel_query` | [`ecs/parallel_query.rs`](./ecs/parallel_query.rs) | Illustrates parallel queries with `ParallelIterator`
diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
index eb513868d1896..9893bfafa409d 100644
--- a/examples/ecs/generic_system.rs
+++ b/examples/ecs/generic_system.rs
@@ -20,6 +20,7 @@ fn main() {
         .add_system_set(SystemSet::on_update(AppState::MainMenu).with_system(transition_to_in_game))
         // add the cleanup systems
         .add_system_set(
+            // Pass in the types your system should operate on using the ::<T> (turbofish) syntax
             SystemSet::on_exit(AppState::MainMenu).with_system(cleanup_system::<MenuClose>),
         )
         .add_system_set(
@@ -58,6 +59,8 @@ fn transition_to_in_game(mut state: ResMut<State<AppState>>, keyboard_input: Res
     }
 }
 
+// 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() {
         commands.entity(e).despawn_recursive();

From 1f63e1e51af582a015b91fb4411b6f19f86843a5 Mon Sep 17 00:00:00 2001
From: Brandon Janson <bjanson28@gmail.com>
Date: Mon, 13 Sep 2021 21:34:35 +1000
Subject: [PATCH 4/9] Add comment and name all systems with 'system'

---
 examples/ecs/generic_system.rs | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
index 9893bfafa409d..fb1fdfb13a75b 100644
--- a/examples/ecs/generic_system.rs
+++ b/examples/ecs/generic_system.rs
@@ -1,5 +1,17 @@
 use bevy::{ecs::component::Component, prelude::*};
 
+/// Generic types allow us to reuse logic across many related systems,
+/// allowing us to specialize our function's behavior based on which type (or types) are passed in.
+///
+/// This is commonly useful for working on related components or resources,
+/// where we want to have unique types for querying purposes but want them all to work the same way.
+/// This is particularly powerful when combined with user-defined traits to add more functionality to these related types.
+/// Remember to insert a specialized copy of the system into the schedule for each type that you want to operate on!
+///
+/// For more advice on working with generic types in Rust, check out https://doc.rust-lang.org/book/ch10-01-syntax.html
+// or https://doc.rust-lang.org/rust-by-example/generics.html
+
+
 #[derive(Debug, Clone, Eq, PartialEq, Hash)]
 enum AppState {
     MainMenu,
@@ -15,9 +27,9 @@ fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
         .add_state(AppState::MainMenu)
-        .add_startup_system(setup)
-        .add_system(print_text)
-        .add_system_set(SystemSet::on_update(AppState::MainMenu).with_system(transition_to_in_game))
+        .add_startup_system(setup_system)
+        .add_system(print_text_system)
+        .add_system_set(SystemSet::on_update(AppState::MainMenu).with_system(transition_to_in_game_system))
         // add the cleanup systems
         .add_system_set(
             // Pass in the types your system should operate on using the ::<T> (turbofish) syntax
@@ -29,7 +41,7 @@ fn main() {
         .run();
 }
 
-fn setup(mut commands: Commands) {
+fn setup_system(mut commands: Commands) {
     commands
         .spawn()
         .insert(Timer::from_seconds(1.0, true))
@@ -45,7 +57,7 @@ fn setup(mut commands: Commands) {
         .insert(LevelUnload);
 }
 
-fn print_text(time: Res<Time>, mut query: Query<(&mut Timer, &TextToPrint)>) {
+fn print_text_system(time: Res<Time>, mut query: Query<(&mut Timer, &TextToPrint)>) {
     for (mut timer, text) in query.iter_mut() {
         if timer.tick(time.delta()).just_finished() {
             info!("{}", text.0);
@@ -53,7 +65,7 @@ fn print_text(time: Res<Time>, mut query: Query<(&mut Timer, &TextToPrint)>) {
     }
 }
 
-fn transition_to_in_game(mut state: ResMut<State<AppState>>, keyboard_input: Res<Input<KeyCode>>) {
+fn transition_to_in_game_system(mut state: ResMut<State<AppState>>, keyboard_input: Res<Input<KeyCode>>) {
     if keyboard_input.pressed(KeyCode::Space) {
         state.set(AppState::InGame).unwrap();
     }

From bce17e53eb282669ebea51e0becc08fd9400eeb9 Mon Sep 17 00:00:00 2001
From: Brandon Janson <bjanson28@gmail.com>
Date: Mon, 13 Sep 2021 21:39:13 +1000
Subject: [PATCH 5/9] cargo fmt

---
 examples/ecs/generic_system.rs | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
index fb1fdfb13a75b..8437ffc246117 100644
--- a/examples/ecs/generic_system.rs
+++ b/examples/ecs/generic_system.rs
@@ -11,7 +11,6 @@ use bevy::{ecs::component::Component, prelude::*};
 /// For more advice on working with generic types in Rust, check out https://doc.rust-lang.org/book/ch10-01-syntax.html
 // or https://doc.rust-lang.org/rust-by-example/generics.html
 
-
 #[derive(Debug, Clone, Eq, PartialEq, Hash)]
 enum AppState {
     MainMenu,
@@ -29,7 +28,9 @@ fn main() {
         .add_state(AppState::MainMenu)
         .add_startup_system(setup_system)
         .add_system(print_text_system)
-        .add_system_set(SystemSet::on_update(AppState::MainMenu).with_system(transition_to_in_game_system))
+        .add_system_set(
+            SystemSet::on_update(AppState::MainMenu).with_system(transition_to_in_game_system),
+        )
         // add the cleanup systems
         .add_system_set(
             // Pass in the types your system should operate on using the ::<T> (turbofish) syntax
@@ -65,7 +66,10 @@ fn print_text_system(time: Res<Time>, mut query: Query<(&mut Timer, &TextToPrint
     }
 }
 
-fn transition_to_in_game_system(mut state: ResMut<State<AppState>>, keyboard_input: Res<Input<KeyCode>>) {
+fn transition_to_in_game_system(
+    mut state: ResMut<State<AppState>>,
+    keyboard_input: Res<Input<KeyCode>>,
+) {
     if keyboard_input.pressed(KeyCode::Space) {
         state.set(AppState::InGame).unwrap();
     }

From 554fdf9386d93c22eb37b8a9319f618bc965bfc4 Mon Sep 17 00:00:00 2001
From: B-Janson <brandon@canva.com>
Date: Wed, 22 Sep 2021 16:35:14 +1000
Subject: [PATCH 6/9] Update examples/ecs/generic_system.rs

Co-authored-by: Alexander Sepity <ratysz@gmail.com>
---
 examples/ecs/generic_system.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
index 8437ffc246117..610a3e8a1f020 100644
--- a/examples/ecs/generic_system.rs
+++ b/examples/ecs/generic_system.rs
@@ -9,7 +9,7 @@ use bevy::{ecs::component::Component, prelude::*};
 /// Remember to insert a specialized copy of the system into the schedule for each type that you want to operate on!
 ///
 /// For more advice on working with generic types in Rust, check out https://doc.rust-lang.org/book/ch10-01-syntax.html
-// or https://doc.rust-lang.org/rust-by-example/generics.html
+/// or https://doc.rust-lang.org/rust-by-example/generics.html
 
 #[derive(Debug, Clone, Eq, PartialEq, Hash)]
 enum AppState {

From ddd1136fee4e3011424377b89e4ad5160907fcf3 Mon Sep 17 00:00:00 2001
From: Brandon Janson <bjanson28@gmail.com>
Date: Tue, 8 Feb 2022 18:24:55 +1100
Subject: [PATCH 7/9] update to 0.6

---
 examples/ecs/generic_system.rs | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
index 610a3e8a1f020..86abe595e4b4c 100644
--- a/examples/ecs/generic_system.rs
+++ b/examples/ecs/generic_system.rs
@@ -17,9 +17,16 @@ enum AppState {
     InGame,
 }
 
+#[derive(Component)]
 struct TextToPrint(String);
 
+#[derive(Component)]
+struct Timer(bevy::prelude::Timer);
+
+#[derive(Component)]
 struct MenuClose;
+
+#[derive(Component)]
 struct LevelUnload;
 
 fn main() {
@@ -45,7 +52,7 @@ fn main() {
 fn setup_system(mut commands: Commands) {
     commands
         .spawn()
-        .insert(Timer::from_seconds(1.0, true))
+        .insert(Timer(bevy::prelude::Timer::from_seconds(1.0, true)))
         .insert(TextToPrint(
             "I will print until you press space.".to_string(),
         ))
@@ -53,14 +60,14 @@ fn setup_system(mut commands: Commands) {
 
     commands
         .spawn()
-        .insert(Timer::from_seconds(1.0, true))
+        .insert(Timer(bevy::prelude::Timer::from_seconds(1.0, true)))
         .insert(TextToPrint("I will always print".to_string()))
         .insert(LevelUnload);
 }
 
 fn print_text_system(time: Res<Time>, mut query: Query<(&mut Timer, &TextToPrint)>) {
     for (mut timer, text) in query.iter_mut() {
-        if timer.tick(time.delta()).just_finished() {
+        if timer.0.tick(time.delta()).just_finished() {
             info!("{}", text.0);
         }
     }

From 91aa12b1cbde276fa2be8407bfc5cbd329dadd8b Mon Sep 17 00:00:00 2001
From: Brandon Janson <bjanson28@gmail.com>
Date: Tue, 8 Feb 2022 18:54:04 +1100
Subject: [PATCH 8/9] pass ci

---
 examples/ecs/generic_system.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
index 86abe595e4b4c..9c2bfcc2187f1 100644
--- a/examples/ecs/generic_system.rs
+++ b/examples/ecs/generic_system.rs
@@ -8,8 +8,8 @@ use bevy::{ecs::component::Component, prelude::*};
 /// This is particularly powerful when combined with user-defined traits to add more functionality to these related types.
 /// Remember to insert a specialized copy of the system into the schedule for each type that you want to operate on!
 ///
-/// For more advice on working with generic types in Rust, check out https://doc.rust-lang.org/book/ch10-01-syntax.html
-/// or https://doc.rust-lang.org/rust-by-example/generics.html
+/// For more advice on working with generic types in Rust, check out <https://doc.rust-lang.org/book/ch10-01-syntax.html>
+/// or <https://doc.rust-lang.org/rust-by-example/generics.html>
 
 #[derive(Debug, Clone, Eq, PartialEq, Hash)]
 enum AppState {

From ce214dd8e4ed2f0036a33b617d1c3ac46296d588 Mon Sep 17 00:00:00 2001
From: Brandon Janson <bjanson28@gmail.com>
Date: Tue, 8 Feb 2022 19:49:06 +1100
Subject: [PATCH 9/9] Rename timer to PrinterTick

---
 examples/ecs/generic_system.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/examples/ecs/generic_system.rs b/examples/ecs/generic_system.rs
index 9c2bfcc2187f1..ee4aab8f631b9 100644
--- a/examples/ecs/generic_system.rs
+++ b/examples/ecs/generic_system.rs
@@ -21,7 +21,7 @@ enum AppState {
 struct TextToPrint(String);
 
 #[derive(Component)]
-struct Timer(bevy::prelude::Timer);
+struct PrinterTick(bevy::prelude::Timer);
 
 #[derive(Component)]
 struct MenuClose;
@@ -52,7 +52,7 @@ fn main() {
 fn setup_system(mut commands: Commands) {
     commands
         .spawn()
-        .insert(Timer(bevy::prelude::Timer::from_seconds(1.0, true)))
+        .insert(PrinterTick(bevy::prelude::Timer::from_seconds(1.0, true)))
         .insert(TextToPrint(
             "I will print until you press space.".to_string(),
         ))
@@ -60,12 +60,12 @@ fn setup_system(mut commands: Commands) {
 
     commands
         .spawn()
-        .insert(Timer(bevy::prelude::Timer::from_seconds(1.0, true)))
+        .insert(PrinterTick(bevy::prelude::Timer::from_seconds(1.0, true)))
         .insert(TextToPrint("I will always print".to_string()))
         .insert(LevelUnload);
 }
 
-fn print_text_system(time: Res<Time>, mut query: Query<(&mut Timer, &TextToPrint)>) {
+fn print_text_system(time: Res<Time>, mut query: Query<(&mut PrinterTick, &TextToPrint)>) {
     for (mut timer, text) in query.iter_mut() {
         if timer.0.tick(time.delta()).just_finished() {
             info!("{}", text.0);