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>
49 lines
1.5 KiB
Rust
49 lines
1.5 KiB
Rust
use bevy::prelude::*;
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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(setup)
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.add_system(animate_sprite)
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.run();
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}
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#[derive(Component, Deref, DerefMut)]
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struct AnimationTimer(Timer);
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fn animate_sprite(
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time: Res<Time>,
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texture_atlases: Res<Assets<TextureAtlas>>,
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mut query: Query<(
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&mut AnimationTimer,
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&mut TextureAtlasSprite,
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&Handle<TextureAtlas>,
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)>,
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) {
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for (mut timer, mut sprite, texture_atlas_handle) in query.iter_mut() {
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timer.tick(time.delta());
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if timer.just_finished() {
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let texture_atlas = texture_atlases.get(texture_atlas_handle).unwrap();
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sprite.index = (sprite.index + 1) % texture_atlas.textures.len();
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}
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}
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}
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fn setup(
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mut commands: Commands,
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asset_server: Res<AssetServer>,
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mut texture_atlases: ResMut<Assets<TextureAtlas>>,
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) {
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let texture_handle = asset_server.load("textures/rpg/chars/gabe/gabe-idle-run.png");
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let texture_atlas = TextureAtlas::from_grid(texture_handle, Vec2::new(24.0, 24.0), 7, 1);
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let texture_atlas_handle = texture_atlases.add(texture_atlas);
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commands.spawn_bundle(OrthographicCameraBundle::new_2d());
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commands
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.spawn_bundle(SpriteSheetBundle {
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texture_atlas: texture_atlas_handle,
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transform: Transform::from_scale(Vec3::splat(6.0)),
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..default()
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})
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.insert(AnimationTimer(Timer::from_seconds(0.1, true)));
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}
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