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*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>
30 lines
998 B
Rust
30 lines
998 B
Rust
//! Illustrates how to make a single system from multiple functions running in sequence and sharing
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//! their inputs and outputs.
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use anyhow::Result;
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use bevy::prelude::*;
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fn main() {
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App::new()
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.insert_resource(Message("42".to_string()))
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.add_system(parse_message_system.chain(handler_system))
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.run();
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}
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#[derive(Resource, Deref)]
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struct Message(String);
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// this system produces a Result<usize> output by trying to parse the Message resource
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fn parse_message_system(message: Res<Message>) -> Result<usize> {
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Ok(message.parse::<usize>()?)
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}
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// This system takes a Result<usize> input and either prints the parsed value or the error message
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// Try changing the Message resource to something that isn't an integer. You should see the error
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// message printed.
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fn handler_system(In(result): In<Result<usize>>) {
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match result {
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Ok(value) => println!("parsed message: {}", value),
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Err(err) => println!("encountered an error: {:?}", err),
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}
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}
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