Generating a system from a closure taking an arbitrary SystemParam

[Strackeror]

Hi there !
I'm having trouble finding a way to write a function that would build a system from a custom closure, that closure taking an arbitrary SystemParam.

think something like this:

pub fn system_foreach<T, P, F>(app: &mut bevy_app::App, items: Vec<T>, func: F)
where
    T: Send + Sync + 'static,
    P: SystemParam,
    F: Fn(&T, &mut P) + Send + Sync + 'static,
{
    app.add_systems(Update, move |mut param: P| {
        for item in &items {
            func(item, &mut param);
        }
    });
}

#[derive(Resource)]
struct Total(i32);
fn toast(app: &mut App) {
   system_foreach(app, vec![1, 2], |i, a: &mut ResMut<Total>| a.0 += i);
}

this would mean that the 'Total' resource would increment by 3 each update, as the closure is run for all elements of vec![1,2] on each run of the system.

I'm having trouble landing on bounds for P and F to make this function compile in some way. I can kinda make it work by making the closure take a StaticSystemParam<P> but that's very clunky to actually use.

This is currently mostly a thought experiment, to see if I can simplify a pattern in my codebase that I'm seeing repeated a lot, of which this is a simplified version.

[hymm]

The type that a system is passed is actually not SystemParam, but SystemParam::Item. I think you need to change the closure parameter to something like:

   app.add_systems(Update, move |mut param: P::Item<'_, '_>| {

not sure that is valid rust. For a normal function this would look something like:

    fn apply_damage<S: SystemParam>(mut param: S::Item<'_, '_>)
    where
        for<'w, 's> S::Item<'w, 's>: GetDamage,
    {
        param.apply_damage();
    }

[Strackeror]

I think i see the idea, thanks !
But, unless i'm misunderstanding something, this isn't enough:

pub fn system_foreach<T, P, F>(app: &mut bevy_app::App, items: Vec<T>, func: F)
where
    T: Send + Sync + 'static,
    P: SystemParam,
    F: Fn(&T, &mut P::Item<'_, '_>) + Send + Sync + 'static,
{
    app.add_systems(Update, move |mut param: P::Item<'_, '_>| {
        for item in &items {
            func(item, &mut param);
        }
    });
}

this still gives me an error that the closure doesn't implement IntoScheduleConfigs