f16768d868
# Objective A common pattern in Rust is the [newtype](https://doc.rust-lang.org/rust-by-example/generics/new_types.html). This is an especially useful pattern in Bevy as it allows us to give common/foreign types different semantics (such as allowing it to implement `Component` or `FromWorld`) or to simply treat them as a "new type" (clever). For example, it allows us to wrap a common `Vec<String>` and do things like: ```rust #[derive(Component)] struct Items(Vec<String>); fn give_sword(query: Query<&mut Items>) { query.single_mut().0.push(String::from("Flaming Poisoning Raging Sword of Doom")); } ``` > We could then define another struct that wraps `Vec<String>` without anything clashing in the query. However, one of the worst parts of this pattern is the ugly `.0` we have to write in order to access the type we actually care about. This is why people often implement `Deref` and `DerefMut` in order to get around this. Since it's such a common pattern, especially for Bevy, it makes sense to add a derive macro to automatically add those implementations. ## Solution Added a derive macro for `Deref` and another for `DerefMut` (both exported into the prelude). This works on all structs (including tuple structs) as long as they only contain a single field: ```rust #[derive(Deref)] struct Foo(String); #[derive(Deref, DerefMut)] struct Bar { name: String, } ``` This allows us to then remove that pesky `.0`: ```rust #[derive(Component, Deref, DerefMut)] struct Items(Vec<String>); fn give_sword(query: Query<&mut Items>) { query.single_mut().push(String::from("Flaming Poisoning Raging Sword of Doom")); } ``` ### Alternatives There are other alternatives to this such as by using the [`derive_more`](https://crates.io/crates/derive_more) crate. However, it doesn't seem like we need an entire crate just yet since we only need `Deref` and `DerefMut` (for now). ### Considerations One thing to consider is that the Rust std library recommends _not_ using `Deref` and `DerefMut` for things like this: "`Deref` should only be implemented for smart pointers to avoid confusion" ([reference](https://doc.rust-lang.org/std/ops/trait.Deref.html)). Personally, I believe it makes sense to use it in the way described above, but others may disagree. ### Additional Context Discord: https://discord.com/channels/691052431525675048/692572690833473578/956648422163746827 (controversiality discussed [here](https://discord.com/channels/691052431525675048/692572690833473578/956711911481835630)) --- ## Changelog - Add `Deref` derive macro (exported to prelude) - Add `DerefMut` derive macro (exported to prelude) - Updated most newtypes in examples to use one or both derives Co-authored-by: MrGVSV <49806985+MrGVSV@users.noreply.github.com>
74 lines
2.5 KiB
Rust
74 lines
2.5 KiB
Rust
use bevy::{prelude::*, tasks::prelude::*};
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use rand::random;
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#[derive(Component, Deref)]
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struct Velocity(Vec2);
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fn spawn_system(mut commands: Commands, asset_server: Res<AssetServer>) {
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commands.spawn_bundle(OrthographicCameraBundle::new_2d());
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let texture = asset_server.load("branding/icon.png");
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for _ in 0..128 {
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commands
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.spawn_bundle(SpriteBundle {
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texture: texture.clone(),
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transform: Transform::from_scale(Vec3::splat(0.1)),
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..default()
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})
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.insert(Velocity(
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20.0 * Vec2::new(random::<f32>() - 0.5, random::<f32>() - 0.5),
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));
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}
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}
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// Move sprites according to their velocity
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fn move_system(pool: Res<ComputeTaskPool>, mut sprites: Query<(&mut Transform, &Velocity)>) {
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// Compute the new location of each sprite in parallel on the
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// ComputeTaskPool using batches of 32 sprites
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//
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// This example is only for demonstrative purposes. Using a
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// ParallelIterator for an inexpensive operation like addition on only 128
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// elements will not typically be faster than just using a normal Iterator.
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// See the ParallelIterator documentation for more information on when
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// to use or not use ParallelIterator over a normal Iterator.
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sprites.par_for_each_mut(&pool, 32, |(mut transform, velocity)| {
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transform.translation += velocity.extend(0.0);
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});
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}
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// Bounce sprites outside the window
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fn bounce_system(
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pool: Res<ComputeTaskPool>,
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windows: Res<Windows>,
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mut sprites: Query<(&Transform, &mut Velocity)>,
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) {
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let window = windows.primary();
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let width = window.width();
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let height = window.height();
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let left = width / -2.0;
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let right = width / 2.0;
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let bottom = height / -2.0;
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let top = height / 2.0;
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sprites
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// Batch size of 32 is chosen to limit the overhead of
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// ParallelIterator, since negating a vector is very inexpensive.
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.par_for_each_mut(&pool, 32, |(transform, mut v)| {
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if !(left < transform.translation.x
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&& transform.translation.x < right
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&& bottom < transform.translation.y
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&& transform.translation.y < top)
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{
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// For simplicity, just reverse the velocity; don't use realistic bounces
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v.0 = -v.0;
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}
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});
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}
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.add_startup_system(spawn_system)
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.add_system(move_system)
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.add_system(bounce_system)
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.run();
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}
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