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# Objective - Improve error descriptions and help understand how to fix them - I noticed one today that could be expanded, it seemed like a good starting point ## Solution - Start something like https://github.com/rust-lang/rust/tree/master/compiler/rustc_error_codes/src/error_codes - Remove sentence about Rust mutability rules which is not very helpful in the error message I decided to start the error code with B for Bevy so that they're not confused with error code from rust (which starts with E) Longer term, there are a few more evolutions that can continue this: - the code samples should be compiled check, and even executed for some of them to check they have the correct error code in a panic - the error could be build on a page in the website like https://doc.rust-lang.org/error-index.html - most panic should have their own error code
1.5 KiB
1.5 KiB
B0002
To keep Rust rules on references (either one mutable reference or any number of immutable references) on a resource, it is not possible to have more than one resource of a kind if one is mutable in the same system. This can happen between Res<T> and ResMut<T> for the same T, or between NonSend<T> and NonSendMut<T> for the same T.
Erroneous code example:
use bevy::prelude::*;
fn update_materials(
mut material_updater: ResMut<Assets<ColorMaterial>>,
current_materials: Res<Assets<ColorMaterial>>,
) {
// ...
}
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_system(update_materials)
.run();
}
This will panic, as it's not possible to have both a mutable and an immutable resource on State at the same time.
As a mutable resource already provide access to the current resource value, you can remove the immutable resource.
use bevy::prelude::*;
fn update_materials(
mut material_updater: ResMut<Assets<ColorMaterial>>,
) {
// ...
}
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_system(update_materials)
.run();
}