Understanding Systems & the Bevy Runtime

[cadojo]

I'm a very early beginner with bevy; congratulations on the excellent work here! Reading through examples, it seems like you can define arguments to your system functions in any order. I also understand that all types must be unique. For example...

//
// From the official Bevy examples...
// 

fn greet_people(
    time: Res<Time>, mut timer: ResMut<GreetTimer>, query: Query<&Name, With<Person>>) {
    // update our timer with the time elapsed since the last update
    // if that caused the timer to finish, we say hello to everyone
    if timer.0.tick(time.delta()).just_finished() {
        for name in &query {
            println!("hello {}!", name.0);
        }
    }
}

Originally greet_people included only the query parameter. Ultimately the time parameter was added to prevent the function from running too often. Either way, the function was added to the App by .add_system(greet_people).

How does bevy know what arguments to pass to each system?

[MrGVSV]

This post by @PROMETHIA-27 might help shed some light. 🙂