Repeat systems

[jim-ec]

I want to repeat a system based on a count variable. How would I achieve that?

A non-compiling snippet outlining my problem:

use bevy::prelude::*;

fn main() {
    App::new()
        // Does not work, add_systems only accepts tuples:
        .add_systems(std::iter::repeat(my_system).take(5))
        .run();
}

fn my_system() {
    println!("Hello world");
}

[TimJentzsch]

This depends on multiple factors:

• Do you want to repeat the system's functionality within a frame or for a defined number of frames?
• Is the number of repetitions fixed once the app has been constructed or could it change every frame?
• Which part of your app should be able to modify the number of repetitions?

For example, if you want to repeat the system's functionality within a frame, have the number of repetitions be variable and modified by other systems in your app, I would do the following:

• Introduce a Resource struct wrapping usize to define the repetition count:

  #[derive(Resource)]
  struct RepetitionCount(usize);

• Initialize the resource to the count you want to start with.

• Modify your system's function signature to pull in the resource:

  fn my_system(repetition_count: Res<RepetitionCount>, ...) { ... }

• Wrap the body of your system in a loop to implement the repetition:

  for _ in (0..repetition_count.0) { ... }

• In the system that should modify the repetition count, pull in ResMut of the count and change it

• Schedule the modifying system to run before my_system

(I didn't check if the example code actually compiles so you might need to adjust it a bit)

[jim-ec]

Thank you. I was hoping there was some kind of system combinator, but this solution also does the job.