992681b59b
*This PR description is an edited copy of #5007, written by @alice-i-cecile.* # Objective Follow-up to https://github.com/bevyengine/bevy/pull/2254. The `Resource` trait currently has a blanket implementation for all types that meet its bounds. While ergonomic, this results in several drawbacks: * it is possible to make confusing, silent mistakes such as inserting a function pointer (Foo) rather than a value (Foo::Bar) as a resource * it is challenging to discover if a type is intended to be used as a resource * we cannot later add customization options (see the [RFC](https://github.com/bevyengine/rfcs/blob/main/rfcs/27-derive-component.md) for the equivalent choice for Component). * dependencies can use the same Rust type as a resource in invisibly conflicting ways * raw Rust types used as resources cannot preserve privacy appropriately, as anyone able to access that type can read and write to internal values * we cannot capture a definitive list of possible resources to display to users in an editor ## Notes to reviewers * Review this commit-by-commit; there's effectively no back-tracking and there's a lot of churn in some of these commits. *ira: My commits are not as well organized :')* * I've relaxed the bound on Local to Send + Sync + 'static: I don't think these concerns apply there, so this can keep things simple. Storing e.g. a u32 in a Local is fine, because there's a variable name attached explaining what it does. * I think this is a bad place for the Resource trait to live, but I've left it in place to make reviewing easier. IMO that's best tackled with https://github.com/bevyengine/bevy/issues/4981. ## Changelog `Resource` is no longer automatically implemented for all matching types. Instead, use the new `#[derive(Resource)]` macro. ## Migration Guide Add `#[derive(Resource)]` to all types you are using as a resource. If you are using a third party type as a resource, wrap it in a tuple struct to bypass orphan rules. Consider deriving `Deref` and `DerefMut` to improve ergonomics. `ClearColor` no longer implements `Component`. Using `ClearColor` as a component in 0.8 did nothing. Use the `ClearColorConfig` in the `Camera3d` and `Camera2d` components instead. Co-authored-by: Alice <alice.i.cecile@gmail.com> Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> Co-authored-by: devil-ira <justthecooldude@gmail.com> Co-authored-by: Carter Anderson <mcanders1@gmail.com>
48 lines
1.2 KiB
Rust
48 lines
1.2 KiB
Rust
//! This example creates a custom [`SystemParam`] struct that counts the number of players.
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use bevy::{ecs::system::SystemParam, prelude::*};
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fn main() {
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App::new()
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.insert_resource(PlayerCount(0))
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.add_startup_system(spawn)
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.add_system(count_players)
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.run();
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}
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#[derive(Component)]
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pub struct Player;
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#[derive(Resource)]
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pub struct PlayerCount(usize);
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/// The [`SystemParam`] struct can contain any types that can also be included in a
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/// system function signature.
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///
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/// In this example, it includes a query and a mutable resource.
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#[derive(SystemParam)]
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struct PlayerCounter<'w, 's> {
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players: Query<'w, 's, &'static Player>,
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count: ResMut<'w, PlayerCount>,
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}
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impl<'w, 's> PlayerCounter<'w, 's> {
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fn count(&mut self) {
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self.count.0 = self.players.iter().len();
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}
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}
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/// Spawn some players to count
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fn spawn(mut commands: Commands) {
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commands.spawn().insert(Player);
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commands.spawn().insert(Player);
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commands.spawn().insert(Player);
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}
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/// The [`SystemParam`] can be used directly in a system argument.
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fn count_players(mut counter: PlayerCounter) {
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counter.count();
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println!("{} players in the game", counter.count.0);
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}
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