Crate bevy_mod_try_system

bevy_mod_try_system provides an extension trait for bevy systems that output Result types which can distinctly pipe Err and Ok values to separate output systems.

This is achieved via the system.pipe_err(err_system) method, which passes Err variants as input to the err_system system, and passes Ok variants to subsequent pipe calls.

In particular, this is useful for managing application-level error context. Since the most common (at least to start) error handling technique might be “log the error”, a utility log_err method, which calls bevy::log::error! on any Err results, is also provided.

Example

In this example, we add an error to a bucket every other update.

use bevy::prelude::*;
use bevy_mod_try_system::*;

#[derive(Debug)]
struct TestError;

#[derive(Default, Resource)]
struct Bucket(Vec<TestError>);

// N.B. We could use `?` in this system, which is convenient.
fn increment_and_error_if_even(mut counter: Local<usize>) -> Result<(), TestError> {
    *counter += 1;
    if *counter % 2 == 1 {
        Ok(())
    } else {
        Err(TestError)
    }
}

fn handle_error(In(error): In<TestError>, mut bucket: ResMut<Bucket>) {
    bucket.0.push(error);
}

fn main() {
    let mut app = App::new();
    app.init_resource::<Bucket>();
    app.add_systems(Update, increment_and_error_if_even.pipe_err(handle_error));
    assert_eq!(app.world().resource::<Bucket>().0.len(), 0);
    app.update();
    assert_eq!(app.world().resource::<Bucket>().0.len(), 0);
    app.update();
    assert_eq!(app.world().resource::<Bucket>().0.len(), 1);
    app.update();
    assert_eq!(app.world().resource::<Bucket>().0.len(), 1);
}

Consider using or referencing bevy_anyhow_alerts to see how to extend this to manage system- and application-level errors.

Traits

• TrySystemExt
  Any system that outputs a Result is a TrySystem.

Type Aliases

• LogErrorsSystem
  An AdapterSystem for systems that return Results and want to log errors.
• TrySystem
  A CombinatorSystem for systems that return Results and handle errors.