From 85ced1ec779fed2eb99116a24ef3d313b166ac82 Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Tue, 19 Jan 2021 19:44:43 +0300
Subject: [PATCH 01/14] get_unique and get_unique_mut

---
 .../bevy_ecs/src/system/query/extensions.rs   | 59 +++++++++++++++++++
 crates/bevy_ecs/src/system/query/mod.rs       |  1 +
 2 files changed, 60 insertions(+)
 create mode 100644 crates/bevy_ecs/src/system/query/extensions.rs

diff --git a/crates/bevy_ecs/src/system/query/extensions.rs b/crates/bevy_ecs/src/system/query/extensions.rs
new file mode 100644
index 0000000000000..da293e84c426f
--- /dev/null
+++ b/crates/bevy_ecs/src/system/query/extensions.rs
@@ -0,0 +1,59 @@
+use std::fmt::Debug;
+
+use thiserror::Error;
+
+use crate::{Fetch, Query, QueryFilter, ReadOnlyFetch, WorldQuery};
+
+impl<'a, Q: WorldQuery, F: QueryFilter> Query<'a, Q, F> {
+    pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>>
+    where
+        Q::Fetch: ReadOnlyFetch,
+    {
+        let mut query = self.iter();
+        let first = query.next();
+        let extra_count = query.count();
+
+        match (first, extra_count) {
+            (Some(r), 0) => Ok(r),
+            (None, _) => Err(OnlyQueryError::NoEntities(std::any::type_name::<Self>())),
+            (Some(r), extra) => Err(OnlyQueryError::MultipleEntities(
+                r,
+                extra,
+                std::any::type_name::<Self>(),
+            )),
+        }
+    }
+
+    pub fn get_unique_mut(&mut self) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>> {
+        let mut query = self.iter_mut();
+        let first = query.next();
+        let extra_count = query.count();
+
+        match (first, extra_count) {
+            (Some(r), 0) => Ok(r),
+            (None, _) => Err(OnlyQueryError::NoEntities(std::any::type_name::<Self>())),
+            (Some(r), extra) => Err(OnlyQueryError::MultipleEntities(
+                r,
+                extra,
+                std::any::type_name::<Self>(),
+            )),
+        }
+    }
+}
+
+#[derive(Error)]
+pub enum OnlyQueryError<'a, Q: WorldQuery> {
+    #[error("No entities fit the query {0}")]
+    NoEntities(&'static str),
+    #[error("Multiple entities ({1} extra) fit the query {2}!")]
+    MultipleEntities(<Q::Fetch as Fetch<'a>>::Item, usize, &'static str),
+}
+
+impl<'a, Q: WorldQuery> Debug for OnlyQueryError<'a, Q> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            OnlyQueryError::NoEntities(_) => f.debug_tuple("NoEntities").finish(),
+            OnlyQueryError::MultipleEntities(_, _, _) => f.debug_tuple("MultipleEntities").finish(),
+        }
+    }
+}
diff --git a/crates/bevy_ecs/src/system/query/mod.rs b/crates/bevy_ecs/src/system/query/mod.rs
index 60a309a029b76..40a37b995105b 100644
--- a/crates/bevy_ecs/src/system/query/mod.rs
+++ b/crates/bevy_ecs/src/system/query/mod.rs
@@ -1,4 +1,5 @@
 mod query_set;
+mod extensions;
 pub use query_set::*;
 
 use crate::{

From 573f293048edbd4133dc3b04e4616bab91bc2f29 Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Tue, 19 Jan 2021 20:50:06 +0300
Subject: [PATCH 02/14] Documentation + update breakout example

---
 crates/bevy_ecs/src/system/query/extensions.rs |  6 +++++-
 crates/bevy_ecs/src/system/query/mod.rs        |  2 +-
 examples/game/breakout.rs                      | 10 ++++------
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/crates/bevy_ecs/src/system/query/extensions.rs b/crates/bevy_ecs/src/system/query/extensions.rs
index da293e84c426f..8022d86ada2ff 100644
--- a/crates/bevy_ecs/src/system/query/extensions.rs
+++ b/crates/bevy_ecs/src/system/query/extensions.rs
@@ -5,6 +5,7 @@ use thiserror::Error;
 use crate::{Fetch, Query, QueryFilter, ReadOnlyFetch, WorldQuery};
 
 impl<'a, Q: WorldQuery, F: QueryFilter> Query<'a, Q, F> {
+    /// Takes exactly one result from the query. If there is 0 or <1 results, this will return an error instead.
     pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>>
     where
         Q::Fetch: ReadOnlyFetch,
@@ -24,7 +25,10 @@ impl<'a, Q: WorldQuery, F: QueryFilter> Query<'a, Q, F> {
         }
     }
 
-    pub fn get_unique_mut(&mut self) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>> {
+    /// See [`Query::get_unique`]
+    pub fn get_unique_mut(
+        &mut self,
+    ) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>> {
         let mut query = self.iter_mut();
         let first = query.next();
         let extra_count = query.count();
diff --git a/crates/bevy_ecs/src/system/query/mod.rs b/crates/bevy_ecs/src/system/query/mod.rs
index 40a37b995105b..9c0fe694f077b 100644
--- a/crates/bevy_ecs/src/system/query/mod.rs
+++ b/crates/bevy_ecs/src/system/query/mod.rs
@@ -1,5 +1,5 @@
-mod query_set;
 mod extensions;
+mod query_set;
 pub use query_set::*;
 
 use crate::{
diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 3d52641803c56..e4b5765f26fd8 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -162,7 +162,7 @@ fn paddle_movement_system(
     keyboard_input: Res<Input<KeyCode>>,
     mut query: Query<(&Paddle, &mut Transform)>,
 ) {
-    for (paddle, mut transform) in query.iter_mut() {
+    if let Ok((paddle, mut transform)) = query.get_unique_mut() {
         let mut direction = 0.0;
         if keyboard_input.pressed(KeyCode::Left) {
             direction -= 1.0;
@@ -184,15 +184,13 @@ fn ball_movement_system(time: Res<Time>, mut ball_query: Query<(&Ball, &mut Tran
     // clamp the timestep to stop the ball from escaping when the game starts
     let delta_seconds = f32::min(0.2, time.delta_seconds());
 
-    for (ball, mut transform) in ball_query.iter_mut() {
+    if let Ok((ball, mut transform)) = ball_query.get_unique_mut() {
         transform.translation += ball.velocity * delta_seconds;
     }
 }
 
 fn scoreboard_system(scoreboard: Res<Scoreboard>, mut query: Query<&mut Text>) {
-    for mut text in query.iter_mut() {
-        text.value = format!("Score: {}", scoreboard.score);
-    }
+    query.get_unique_mut().unwrap().value = format!("Score: {}", scoreboard.score)
 }
 
 fn ball_collision_system(
@@ -201,7 +199,7 @@ fn ball_collision_system(
     mut ball_query: Query<(&mut Ball, &Transform, &Sprite)>,
     collider_query: Query<(Entity, &Collider, &Transform, &Sprite)>,
 ) {
-    for (mut ball, ball_transform, sprite) in ball_query.iter_mut() {
+    if let Ok((mut ball, ball_transform, sprite)) = ball_query.get_unique_mut() {
         let ball_size = sprite.size;
         let velocity = &mut ball.velocity;
 

From 326dea97a241c19c9e7d68f2faf042cc07610741 Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Tue, 19 Jan 2021 21:09:57 +0300
Subject: [PATCH 03/14] Doc fix

---
 crates/bevy_ecs/src/system/query/extensions.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/bevy_ecs/src/system/query/extensions.rs b/crates/bevy_ecs/src/system/query/extensions.rs
index 8022d86ada2ff..53252aabeb0ff 100644
--- a/crates/bevy_ecs/src/system/query/extensions.rs
+++ b/crates/bevy_ecs/src/system/query/extensions.rs
@@ -5,7 +5,7 @@ use thiserror::Error;
 use crate::{Fetch, Query, QueryFilter, ReadOnlyFetch, WorldQuery};
 
 impl<'a, Q: WorldQuery, F: QueryFilter> Query<'a, Q, F> {
-    /// Takes exactly one result from the query. If there is 0 or <1 results, this will return an error instead.
+    /// Takes exactly one result from the query. If there no results, or more than 1 result, this will return an error instead.
     pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>>
     where
         Q::Fetch: ReadOnlyFetch,

From 93f07e39222ac26b1da11e28b312c271c5526ce0 Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Tue, 19 Jan 2021 21:10:49 +0300
Subject: [PATCH 04/14] Doc fix

---
 crates/bevy_ecs/src/system/query/extensions.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/bevy_ecs/src/system/query/extensions.rs b/crates/bevy_ecs/src/system/query/extensions.rs
index 53252aabeb0ff..232fb08ff135c 100644
--- a/crates/bevy_ecs/src/system/query/extensions.rs
+++ b/crates/bevy_ecs/src/system/query/extensions.rs
@@ -5,7 +5,7 @@ use thiserror::Error;
 use crate::{Fetch, Query, QueryFilter, ReadOnlyFetch, WorldQuery};
 
 impl<'a, Q: WorldQuery, F: QueryFilter> Query<'a, Q, F> {
-    /// Takes exactly one result from the query. If there no results, or more than 1 result, this will return an error instead.
+    /// Takes exactly one result from the query. If there are no results, or more than 1 result, this will return an error instead.
     pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>>
     where
         Q::Fetch: ReadOnlyFetch,

From 964bfcfe692f2f4a7bfffa02fd3f994fa8d3011b Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Wed, 20 Jan 2021 00:39:11 +0300
Subject: [PATCH 05/14] Implement suggestions

---
 .../bevy_ecs/src/system/query/extensions.rs   | 57 ++++++++++---------
 1 file changed, 29 insertions(+), 28 deletions(-)

diff --git a/crates/bevy_ecs/src/system/query/extensions.rs b/crates/bevy_ecs/src/system/query/extensions.rs
index 232fb08ff135c..ebd3ce8daf819 100644
--- a/crates/bevy_ecs/src/system/query/extensions.rs
+++ b/crates/bevy_ecs/src/system/query/extensions.rs
@@ -6,58 +6,59 @@ use crate::{Fetch, Query, QueryFilter, ReadOnlyFetch, WorldQuery};
 
 impl<'a, Q: WorldQuery, F: QueryFilter> Query<'a, Q, F> {
     /// Takes exactly one result from the query. If there are no results, or more than 1 result, this will return an error instead.
-    pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>>
+    pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>>
     where
         Q::Fetch: ReadOnlyFetch,
     {
         let mut query = self.iter();
         let first = query.next();
-        let extra_count = query.count();
-
-        match (first, extra_count) {
-            (Some(r), 0) => Ok(r),
-            (None, _) => Err(OnlyQueryError::NoEntities(std::any::type_name::<Self>())),
-            (Some(r), extra) => Err(OnlyQueryError::MultipleEntities(
-                r,
-                extra,
-                std::any::type_name::<Self>(),
-            )),
+        let extra = query.next().is_some();
+
+        match (first, extra) {
+            (Some(r), false) => Ok(r),
+            (None, _) => Err(UniqueQueryError::NoEntities(std::any::type_name::<Self>())),
+            (Some(r), _) => Err(UniqueQueryError::MultipleEntities {
+                result: r,
+                query_name: std::any::type_name::<Self>(),
+            }),
         }
     }
 
     /// See [`Query::get_unique`]
     pub fn get_unique_mut(
         &mut self,
-    ) -> Result<<Q::Fetch as Fetch<'_>>::Item, OnlyQueryError<'_, Q>> {
+    ) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>> {
         let mut query = self.iter_mut();
         let first = query.next();
-        let extra_count = query.count();
-
-        match (first, extra_count) {
-            (Some(r), 0) => Ok(r),
-            (None, _) => Err(OnlyQueryError::NoEntities(std::any::type_name::<Self>())),
-            (Some(r), extra) => Err(OnlyQueryError::MultipleEntities(
-                r,
-                extra,
-                std::any::type_name::<Self>(),
-            )),
+        let extra = query.next().is_some();
+
+        match (first, extra) {
+            (Some(r), false) => Ok(r),
+            (None, _) => Err(UniqueQueryError::NoEntities(std::any::type_name::<Self>())),
+            (Some(r), _) => Err(UniqueQueryError::MultipleEntities {
+                result: r,
+                query_name: std::any::type_name::<Self>(),
+            }),
         }
     }
 }
 
 #[derive(Error)]
-pub enum OnlyQueryError<'a, Q: WorldQuery> {
+pub enum UniqueQueryError<'a, Q: WorldQuery> {
     #[error("No entities fit the query {0}")]
     NoEntities(&'static str),
-    #[error("Multiple entities ({1} extra) fit the query {2}!")]
-    MultipleEntities(<Q::Fetch as Fetch<'a>>::Item, usize, &'static str),
+    #[error("Multiple entities fit the query {query_name}!")]
+    MultipleEntities {
+        result: <Q::Fetch as Fetch<'a>>::Item,
+        query_name: &'static str,
+    },
 }
 
-impl<'a, Q: WorldQuery> Debug for OnlyQueryError<'a, Q> {
+impl<'a, Q: WorldQuery> Debug for UniqueQueryError<'a, Q> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            OnlyQueryError::NoEntities(_) => f.debug_tuple("NoEntities").finish(),
-            OnlyQueryError::MultipleEntities(_, _, _) => f.debug_tuple("MultipleEntities").finish(),
+            Self::NoEntities(_) => f.debug_tuple("NoEntities").finish(),
+            Self::MultipleEntities { .. } => f.debug_tuple("MultipleEntities").finish(),
         }
     }
 }

From 370c04466eea7b98eb0e0c85c8575313f5e3fe08 Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Fri, 22 Jan 2021 21:46:28 +0300
Subject: [PATCH 06/14] Update new example

---
 examples/game/alien_cake_addict.rs | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/examples/game/alien_cake_addict.rs b/examples/game/alien_cake_addict.rs
index 9468fd714ff17..c7f3d67b020e7 100644
--- a/examples/game/alien_cake_addict.rs
+++ b/examples/game/alien_cake_addict.rs
@@ -337,9 +337,7 @@ fn rotate_bonus(game: Res<Game>, time: Res<Time>, mut transforms: Query<&mut Tra
 
 // update the score displayed during the game
 fn scoreboard_system(game: Res<Game>, mut query: Query<&mut Text>) {
-    for mut text in query.iter_mut() {
-        text.value = format!("Sugar Rush: {}", game.score);
-    }
+    query.get_unique_mut().unwrap().value = format!("Sugar Rush: {}", game.score);
 }
 
 // restart the game when pressing spacebar

From 5af71fb9eec4c6d9c4d4ab5fc7631d3363d19d8d Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Sat, 6 Mar 2021 00:48:36 +0300
Subject: [PATCH 07/14] Update to latest

---
 crates/bevy_ecs/src/{system => }/query/extensions.rs | 9 +++++++--
 crates/bevy_ecs/src/query/mod.rs                     | 1 +
 2 files changed, 8 insertions(+), 2 deletions(-)
 rename crates/bevy_ecs/src/{system => }/query/extensions.rs (92%)

diff --git a/crates/bevy_ecs/src/system/query/extensions.rs b/crates/bevy_ecs/src/query/extensions.rs
similarity index 92%
rename from crates/bevy_ecs/src/system/query/extensions.rs
rename to crates/bevy_ecs/src/query/extensions.rs
index ebd3ce8daf819..6411fb1e95ebd 100644
--- a/crates/bevy_ecs/src/system/query/extensions.rs
+++ b/crates/bevy_ecs/src/query/extensions.rs
@@ -2,9 +2,14 @@ use std::fmt::Debug;
 
 use thiserror::Error;
 
-use crate::{Fetch, Query, QueryFilter, ReadOnlyFetch, WorldQuery};
+use crate::prelude::Query;
 
-impl<'a, Q: WorldQuery, F: QueryFilter> Query<'a, Q, F> {
+use super::{Fetch, FilterFetch, ReadOnlyFetch, WorldQuery};
+
+impl<'w, Q: WorldQuery, F: WorldQuery> Query<'w, Q, F>
+where
+    F::Fetch: FilterFetch,
+{
     /// Takes exactly one result from the query. If there are no results, or more than 1 result, this will return an error instead.
     pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>>
     where
diff --git a/crates/bevy_ecs/src/query/mod.rs b/crates/bevy_ecs/src/query/mod.rs
index 95b4d7b6e8912..80fd4b4ed7e71 100644
--- a/crates/bevy_ecs/src/query/mod.rs
+++ b/crates/bevy_ecs/src/query/mod.rs
@@ -1,4 +1,5 @@
 mod access;
+mod extensions;
 mod fetch;
 mod filter;
 mod iter;

From cc2f5c916ca02e175fe87979f3e1f9226c058877 Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Sat, 6 Mar 2021 13:30:23 +0300
Subject: [PATCH 08/14] Join impl blocks

---
 crates/bevy_ecs/src/query/extensions.rs | 69 -------------------------
 crates/bevy_ecs/src/query/mod.rs        |  1 -
 crates/bevy_ecs/src/system/query.rs     | 58 ++++++++++++++++++++-
 3 files changed, 57 insertions(+), 71 deletions(-)
 delete mode 100644 crates/bevy_ecs/src/query/extensions.rs

diff --git a/crates/bevy_ecs/src/query/extensions.rs b/crates/bevy_ecs/src/query/extensions.rs
deleted file mode 100644
index 6411fb1e95ebd..0000000000000
--- a/crates/bevy_ecs/src/query/extensions.rs
+++ /dev/null
@@ -1,69 +0,0 @@
-use std::fmt::Debug;
-
-use thiserror::Error;
-
-use crate::prelude::Query;
-
-use super::{Fetch, FilterFetch, ReadOnlyFetch, WorldQuery};
-
-impl<'w, Q: WorldQuery, F: WorldQuery> Query<'w, Q, F>
-where
-    F::Fetch: FilterFetch,
-{
-    /// Takes exactly one result from the query. If there are no results, or more than 1 result, this will return an error instead.
-    pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>>
-    where
-        Q::Fetch: ReadOnlyFetch,
-    {
-        let mut query = self.iter();
-        let first = query.next();
-        let extra = query.next().is_some();
-
-        match (first, extra) {
-            (Some(r), false) => Ok(r),
-            (None, _) => Err(UniqueQueryError::NoEntities(std::any::type_name::<Self>())),
-            (Some(r), _) => Err(UniqueQueryError::MultipleEntities {
-                result: r,
-                query_name: std::any::type_name::<Self>(),
-            }),
-        }
-    }
-
-    /// See [`Query::get_unique`]
-    pub fn get_unique_mut(
-        &mut self,
-    ) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>> {
-        let mut query = self.iter_mut();
-        let first = query.next();
-        let extra = query.next().is_some();
-
-        match (first, extra) {
-            (Some(r), false) => Ok(r),
-            (None, _) => Err(UniqueQueryError::NoEntities(std::any::type_name::<Self>())),
-            (Some(r), _) => Err(UniqueQueryError::MultipleEntities {
-                result: r,
-                query_name: std::any::type_name::<Self>(),
-            }),
-        }
-    }
-}
-
-#[derive(Error)]
-pub enum UniqueQueryError<'a, Q: WorldQuery> {
-    #[error("No entities fit the query {0}")]
-    NoEntities(&'static str),
-    #[error("Multiple entities fit the query {query_name}!")]
-    MultipleEntities {
-        result: <Q::Fetch as Fetch<'a>>::Item,
-        query_name: &'static str,
-    },
-}
-
-impl<'a, Q: WorldQuery> Debug for UniqueQueryError<'a, Q> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Self::NoEntities(_) => f.debug_tuple("NoEntities").finish(),
-            Self::MultipleEntities { .. } => f.debug_tuple("MultipleEntities").finish(),
-        }
-    }
-}
diff --git a/crates/bevy_ecs/src/query/mod.rs b/crates/bevy_ecs/src/query/mod.rs
index 80fd4b4ed7e71..95b4d7b6e8912 100644
--- a/crates/bevy_ecs/src/query/mod.rs
+++ b/crates/bevy_ecs/src/query/mod.rs
@@ -1,5 +1,4 @@
 mod access;
-mod extensions;
 mod fetch;
 mod filter;
 mod iter;
diff --git a/crates/bevy_ecs/src/system/query.rs b/crates/bevy_ecs/src/system/query.rs
index a98f5cd36c63d..93a9676a74ace 100644
--- a/crates/bevy_ecs/src/system/query.rs
+++ b/crates/bevy_ecs/src/system/query.rs
@@ -7,7 +7,7 @@ use crate::{
     world::{Mut, World},
 };
 use bevy_tasks::TaskPool;
-use std::any::TypeId;
+use std::{any::TypeId, fmt::Debug};
 use thiserror::Error;
 
 /// Provides scoped access to a World according to a given [WorldQuery] and query filter
@@ -212,6 +212,42 @@ where
             Err(QueryComponentError::MissingWriteAccess)
         }
     }
+
+    pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>>
+    where
+        Q::Fetch: ReadOnlyFetch,
+    {
+        let mut query = self.iter();
+        let first = query.next();
+        let extra = query.next().is_some();
+
+        match (first, extra) {
+            (Some(r), false) => Ok(r),
+            (None, _) => Err(UniqueQueryError::NoEntities(std::any::type_name::<Self>())),
+            (Some(r), _) => Err(UniqueQueryError::MultipleEntities {
+                result: r,
+                query_name: std::any::type_name::<Self>(),
+            }),
+        }
+    }
+
+    /// See [`Query::get_unique`]
+    pub fn get_unique_mut(
+        &mut self,
+    ) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>> {
+        let mut query = self.iter_mut();
+        let first = query.next();
+        let extra = query.next().is_some();
+
+        match (first, extra) {
+            (Some(r), false) => Ok(r),
+            (None, _) => Err(UniqueQueryError::NoEntities(std::any::type_name::<Self>())),
+            (Some(r), _) => Err(UniqueQueryError::MultipleEntities {
+                result: r,
+                query_name: std::any::type_name::<Self>(),
+            }),
+        }
+    }
 }
 
 /// An error that occurs when retrieving a specific [Entity]'s component from a [Query]
@@ -226,3 +262,23 @@ pub enum QueryComponentError {
     #[error("The requested entity does not exist.")]
     NoSuchEntity,
 }
+
+#[derive(Error)]
+pub enum UniqueQueryError<'a, Q: WorldQuery> {
+    #[error("No entities fit the query {0}")]
+    NoEntities(&'static str),
+    #[error("Multiple entities fit the query {query_name}!")]
+    MultipleEntities {
+        result: <Q::Fetch as Fetch<'a>>::Item,
+        query_name: &'static str,
+    },
+}
+
+impl<'a, Q: WorldQuery> Debug for UniqueQueryError<'a, Q> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::NoEntities(_) => f.debug_tuple("NoEntities").finish(),
+            Self::MultipleEntities { .. } => f.debug_tuple("MultipleEntities").finish(),
+        }
+    }
+}

From 4bc8f0c6ac1b18c685cfc72c2dcd7df3e33d3df6 Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Sat, 6 Mar 2021 13:32:03 +0300
Subject: [PATCH 09/14] Change examples

---
 examples/game/alien_cake_addict.rs | 3 ++-
 examples/game/breakout.rs          | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/examples/game/alien_cake_addict.rs b/examples/game/alien_cake_addict.rs
index af021a5e7afb7..ee8f63a77a21f 100644
--- a/examples/game/alien_cake_addict.rs
+++ b/examples/game/alien_cake_addict.rs
@@ -357,7 +357,8 @@ fn rotate_bonus(game: Res<Game>, time: Res<Time>, mut transforms: Query<&mut Tra
 
 // update the score displayed during the game
 fn scoreboard_system(game: Res<Game>, mut query: Query<&mut Text>) {
-    query.get_unique_mut().unwrap().sections[0].value = format!("Sugar Rush: {}", game.score);
+    let mut text = query.get_unique_mut().unwrap();
+    text.sections[0].value = format!("Sugar Rush: {}", game.score);
 }
 
 // restart the game when pressing spacebar
diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 44514b75ea80f..77b0691f04724 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -202,8 +202,8 @@ fn ball_movement_system(time: Res<Time>, mut ball_query: Query<(&Ball, &mut Tran
 }
 
 fn scoreboard_system(scoreboard: Res<Scoreboard>, mut query: Query<&mut Text>) {
-    query.get_unique_mut().unwrap().sections[1].value = format!("Score: {}", scoreboard.score)
-}
+    let mut text = query.get_unique_mut().unwrap();
+    text.sections[0].value = format!("Score: {}", scoreboard.score);}
 
 fn ball_collision_system(
     mut commands: Commands,

From 435a7f2b214ec4bf7aa47d9054a9406a71549543 Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Sat, 6 Mar 2021 13:57:24 +0300
Subject: [PATCH 10/14] fix formatting

---
 examples/game/breakout.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 77b0691f04724..5497fe63f8050 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -203,7 +203,8 @@ fn ball_movement_system(time: Res<Time>, mut ball_query: Query<(&Ball, &mut Tran
 
 fn scoreboard_system(scoreboard: Res<Scoreboard>, mut query: Query<&mut Text>) {
     let mut text = query.get_unique_mut().unwrap();
-    text.sections[0].value = format!("Score: {}", scoreboard.score);}
+    text.sections[0].value = format!("Score: {}", scoreboard.score);
+}
 
 fn ball_collision_system(
     mut commands: Commands,

From 0be6c8cb10d772b67e871877a1b9824b8288e89f Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Sun, 7 Mar 2021 23:33:33 +0300
Subject: [PATCH 11/14] Refactor code tu use `single`

---
 crates/bevy_ecs/src/system/query.rs | 6 +++---
 examples/game/alien_cake_addict.rs  | 2 +-
 examples/game/breakout.rs           | 8 ++++----
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/crates/bevy_ecs/src/system/query.rs b/crates/bevy_ecs/src/system/query.rs
index 93a9676a74ace..89b93f20f489a 100644
--- a/crates/bevy_ecs/src/system/query.rs
+++ b/crates/bevy_ecs/src/system/query.rs
@@ -213,7 +213,7 @@ where
         }
     }
 
-    pub fn get_unique(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>>
+    pub fn single(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>>
     where
         Q::Fetch: ReadOnlyFetch,
     {
@@ -231,8 +231,8 @@ where
         }
     }
 
-    /// See [`Query::get_unique`]
-    pub fn get_unique_mut(
+    /// See [`Query::single`]
+    pub fn single_mut(
         &mut self,
     ) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>> {
         let mut query = self.iter_mut();
diff --git a/examples/game/alien_cake_addict.rs b/examples/game/alien_cake_addict.rs
index ee8f63a77a21f..325638ff47366 100644
--- a/examples/game/alien_cake_addict.rs
+++ b/examples/game/alien_cake_addict.rs
@@ -357,7 +357,7 @@ fn rotate_bonus(game: Res<Game>, time: Res<Time>, mut transforms: Query<&mut Tra
 
 // update the score displayed during the game
 fn scoreboard_system(game: Res<Game>, mut query: Query<&mut Text>) {
-    let mut text = query.get_unique_mut().unwrap();
+    let mut text = query.single_mut().unwrap();
     text.sections[0].value = format!("Sugar Rush: {}", game.score);
 }
 
diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index 5497fe63f8050..dea6e834c8ac8 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -174,7 +174,7 @@ fn paddle_movement_system(
     keyboard_input: Res<Input<KeyCode>>,
     mut query: Query<(&Paddle, &mut Transform)>,
 ) {
-    if let Ok((paddle, mut transform)) = query.get_unique_mut() {
+    if let Ok((paddle, mut transform)) = query.single_mut() {
         let mut direction = 0.0;
         if keyboard_input.pressed(KeyCode::Left) {
             direction -= 1.0;
@@ -196,13 +196,13 @@ fn ball_movement_system(time: Res<Time>, mut ball_query: Query<(&Ball, &mut Tran
     // clamp the timestep to stop the ball from escaping when the game starts
     let delta_seconds = f32::min(0.2, time.delta_seconds());
 
-    if let Ok((ball, mut transform)) = ball_query.get_unique_mut() {
+    if let Ok((ball, mut transform)) = ball_query.single_mut() {
         transform.translation += ball.velocity * delta_seconds;
     }
 }
 
 fn scoreboard_system(scoreboard: Res<Scoreboard>, mut query: Query<&mut Text>) {
-    let mut text = query.get_unique_mut().unwrap();
+    let mut text = query.single_mut().unwrap();
     text.sections[0].value = format!("Score: {}", scoreboard.score);
 }
 
@@ -212,7 +212,7 @@ fn ball_collision_system(
     mut ball_query: Query<(&mut Ball, &Transform, &Sprite)>,
     collider_query: Query<(Entity, &Collider, &Transform, &Sprite)>,
 ) {
-    if let Ok((mut ball, ball_transform, sprite)) = ball_query.get_unique_mut() {
+    if let Ok((mut ball, ball_transform, sprite)) = ball_query.single_mut() {
         let ball_size = sprite.size;
         let velocity = &mut ball.velocity;
 

From 11c06068d67867f552908e66b3d4a324bd7a175b Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Sun, 7 Mar 2021 23:35:51 +0300
Subject: [PATCH 12/14] Refactor error

---
 crates/bevy_ecs/src/system/query.rs | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/crates/bevy_ecs/src/system/query.rs b/crates/bevy_ecs/src/system/query.rs
index 89b93f20f489a..8fed3e56fe48d 100644
--- a/crates/bevy_ecs/src/system/query.rs
+++ b/crates/bevy_ecs/src/system/query.rs
@@ -213,7 +213,7 @@ where
         }
     }
 
-    pub fn single(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>>
+    pub fn single(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, QuerySingleError<'_, Q>>
     where
         Q::Fetch: ReadOnlyFetch,
     {
@@ -223,8 +223,8 @@ where
 
         match (first, extra) {
             (Some(r), false) => Ok(r),
-            (None, _) => Err(UniqueQueryError::NoEntities(std::any::type_name::<Self>())),
-            (Some(r), _) => Err(UniqueQueryError::MultipleEntities {
+            (None, _) => Err(QuerySingleError::NoEntities(std::any::type_name::<Self>())),
+            (Some(r), _) => Err(QuerySingleError::MultipleEntities {
                 result: r,
                 query_name: std::any::type_name::<Self>(),
             }),
@@ -234,15 +234,15 @@ where
     /// See [`Query::single`]
     pub fn single_mut(
         &mut self,
-    ) -> Result<<Q::Fetch as Fetch<'_>>::Item, UniqueQueryError<'_, Q>> {
+    ) -> Result<<Q::Fetch as Fetch<'_>>::Item, QuerySingleError<'_, Q>> {
         let mut query = self.iter_mut();
         let first = query.next();
         let extra = query.next().is_some();
 
         match (first, extra) {
             (Some(r), false) => Ok(r),
-            (None, _) => Err(UniqueQueryError::NoEntities(std::any::type_name::<Self>())),
-            (Some(r), _) => Err(UniqueQueryError::MultipleEntities {
+            (None, _) => Err(QuerySingleError::NoEntities(std::any::type_name::<Self>())),
+            (Some(r), _) => Err(QuerySingleError::MultipleEntities {
                 result: r,
                 query_name: std::any::type_name::<Self>(),
             }),
@@ -264,7 +264,7 @@ pub enum QueryComponentError {
 }
 
 #[derive(Error)]
-pub enum UniqueQueryError<'a, Q: WorldQuery> {
+pub enum QuerySingleError<'a, Q: WorldQuery> {
     #[error("No entities fit the query {0}")]
     NoEntities(&'static str),
     #[error("Multiple entities fit the query {query_name}!")]
@@ -274,7 +274,7 @@ pub enum UniqueQueryError<'a, Q: WorldQuery> {
     },
 }
 
-impl<'a, Q: WorldQuery> Debug for UniqueQueryError<'a, Q> {
+impl<'a, Q: WorldQuery> Debug for QuerySingleError<'a, Q> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
             Self::NoEntities(_) => f.debug_tuple("NoEntities").finish(),

From e0c7e36cadd48c2174171701e48f322335b5accf Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Sun, 7 Mar 2021 23:41:29 +0300
Subject: [PATCH 13/14] cargo fmt

---
 crates/bevy_ecs/src/system/query.rs | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/crates/bevy_ecs/src/system/query.rs b/crates/bevy_ecs/src/system/query.rs
index 8fed3e56fe48d..621677cd70dc8 100644
--- a/crates/bevy_ecs/src/system/query.rs
+++ b/crates/bevy_ecs/src/system/query.rs
@@ -232,9 +232,7 @@ where
     }
 
     /// See [`Query::single`]
-    pub fn single_mut(
-        &mut self,
-    ) -> Result<<Q::Fetch as Fetch<'_>>::Item, QuerySingleError<'_, Q>> {
+    pub fn single_mut(&mut self) -> Result<<Q::Fetch as Fetch<'_>>::Item, QuerySingleError<'_, Q>> {
         let mut query = self.iter_mut();
         let first = query.next();
         let extra = query.next().is_some();

From 06cd9cda7d1a21bda6f9834a219b9d102e57be1f Mon Sep 17 00:00:00 2001
From: TheRawMeatball <therawmeatball@gmail.com>
Date: Mon, 8 Mar 2021 23:28:19 +0300
Subject: [PATCH 14/14] Remove item from error

---
 crates/bevy_ecs/src/system/query.rs | 38 +++++++++--------------------
 1 file changed, 12 insertions(+), 26 deletions(-)

diff --git a/crates/bevy_ecs/src/system/query.rs b/crates/bevy_ecs/src/system/query.rs
index 621677cd70dc8..d19056b86c42f 100644
--- a/crates/bevy_ecs/src/system/query.rs
+++ b/crates/bevy_ecs/src/system/query.rs
@@ -213,7 +213,7 @@ where
         }
     }
 
-    pub fn single(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, QuerySingleError<'_, Q>>
+    pub fn single(&self) -> Result<<Q::Fetch as Fetch<'_>>::Item, QuerySingleError>
     where
         Q::Fetch: ReadOnlyFetch,
     {
@@ -224,15 +224,14 @@ where
         match (first, extra) {
             (Some(r), false) => Ok(r),
             (None, _) => Err(QuerySingleError::NoEntities(std::any::type_name::<Self>())),
-            (Some(r), _) => Err(QuerySingleError::MultipleEntities {
-                result: r,
-                query_name: std::any::type_name::<Self>(),
-            }),
+            (Some(_), _) => Err(QuerySingleError::MultipleEntities(std::any::type_name::<
+                Self,
+            >())),
         }
     }
 
     /// See [`Query::single`]
-    pub fn single_mut(&mut self) -> Result<<Q::Fetch as Fetch<'_>>::Item, QuerySingleError<'_, Q>> {
+    pub fn single_mut(&mut self) -> Result<<Q::Fetch as Fetch<'_>>::Item, QuerySingleError> {
         let mut query = self.iter_mut();
         let first = query.next();
         let extra = query.next().is_some();
@@ -240,10 +239,9 @@ where
         match (first, extra) {
             (Some(r), false) => Ok(r),
             (None, _) => Err(QuerySingleError::NoEntities(std::any::type_name::<Self>())),
-            (Some(r), _) => Err(QuerySingleError::MultipleEntities {
-                result: r,
-                query_name: std::any::type_name::<Self>(),
-            }),
+            (Some(_), _) => Err(QuerySingleError::MultipleEntities(std::any::type_name::<
+                Self,
+            >())),
         }
     }
 }
@@ -261,22 +259,10 @@ pub enum QueryComponentError {
     NoSuchEntity,
 }
 
-#[derive(Error)]
-pub enum QuerySingleError<'a, Q: WorldQuery> {
+#[derive(Debug, Error)]
+pub enum QuerySingleError {
     #[error("No entities fit the query {0}")]
     NoEntities(&'static str),
-    #[error("Multiple entities fit the query {query_name}!")]
-    MultipleEntities {
-        result: <Q::Fetch as Fetch<'a>>::Item,
-        query_name: &'static str,
-    },
-}
-
-impl<'a, Q: WorldQuery> Debug for QuerySingleError<'a, Q> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Self::NoEntities(_) => f.debug_tuple("NoEntities").finish(),
-            Self::MultipleEntities { .. } => f.debug_tuple("MultipleEntities").finish(),
-        }
-    }
+    #[error("Multiple entities fit the query {0}!")]
+    MultipleEntities(&'static str),
 }