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>
75 lines
2.2 KiB
Rust
75 lines
2.2 KiB
Rust
use bevy::{log::info, prelude::*};
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.init_resource::<Countdown>()
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.add_startup_system(setup)
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.add_system(countdown)
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.add_system(print_when_completed)
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.run();
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}
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#[derive(Component, Deref, DerefMut)]
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pub struct PrintOnCompletionTimer(Timer);
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pub struct Countdown {
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pub percent_trigger: Timer,
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pub main_timer: Timer,
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}
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impl Countdown {
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pub fn new() -> Self {
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Self {
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percent_trigger: Timer::from_seconds(4.0, true),
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main_timer: Timer::from_seconds(20.0, false),
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}
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}
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}
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impl Default for Countdown {
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fn default() -> Self {
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Self::new()
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}
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}
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fn setup(mut commands: Commands) {
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// Add an entity to the world with a timer
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commands
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.spawn()
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.insert(PrintOnCompletionTimer(Timer::from_seconds(5.0, false)));
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}
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/// This system ticks all the `Timer` components on entities within the scene
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/// using bevy's `Time` resource to get the delta between each update.
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fn print_when_completed(time: Res<Time>, mut query: Query<&mut PrintOnCompletionTimer>) {
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for mut timer in query.iter_mut() {
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if timer.tick(time.delta()).just_finished() {
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info!("Entity timer just finished");
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}
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}
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}
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/// This system controls ticking the timer within the countdown resource and
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/// handling its state.
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fn countdown(time: Res<Time>, mut countdown: ResMut<Countdown>) {
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countdown.main_timer.tick(time.delta());
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// The API encourages this kind of timer state checking (if you're only checking for one value)
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// Additionally, `finished()` would accomplish the same thing as `just_finished` due to the
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// timer being repeating, however this makes more sense visually.
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if countdown.percent_trigger.tick(time.delta()).just_finished() {
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if !countdown.main_timer.finished() {
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// Print the percent complete the main timer is.
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info!(
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"Timer is {:0.0}% complete!",
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countdown.main_timer.percent() * 100.0
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);
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} else {
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// The timer has finished so we pause the percent output timer
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countdown.percent_trigger.pause();
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info!("Paused percent trigger timer");
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}
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}
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}
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