Composing Systems

[cab]

I was wondering if there were any provided solutions, "tips", or possible contributions I could make for composing systems.

For example, taking the example system:

let update_positions = SystemBuilder::new("update_positions")
        .write_resource::<ExampleResource1>()
        .read_resource::<ExampleResource2>()
        .with_query(<(Write<Pos>, Read<Vel>)>::query())
        .build(|_, mut world, (res1, res2), query| {
            res1.0 = res2.0.clone(); // Write the mutable resource from the immutable resource

            for (mut pos, vel) in query.iter_mut(&mut world) {
                pos.0 += vel.0;
                pos.1 += vel.1;
                pos.2 += vel.2;
            }
        });

It would be nice to be able to compose the function passed to build to e.g. make this system execute every 1000 milliseconds, something like:

 .build(timed_system(1000, |_, mut world, (res1, res2), query| {
            res1.0 = res2.0.clone(); // Write the mutable resource from the immutable resource

            for (mut pos, vel) in query.iter_mut(&mut world) {
                pos.0 += vel.0;
                pos.1 += vel.1;
                pos.2 += vel.2;
            }
        }));

But if you define some function that takes in a FnMut with the same type parameters as build, the query argument type can no longer be inferred, which makes this difficult to work with. Separately, I think there would be no way to specify what resources the "wrapper" system needs without modifying the scheduler.

However, maybe this is just the wrong approach overall, or I'm looking for something different from legion_systems.

This is maybe related to #31.

And thanks for legion, really enjoying using it so far.

[cab]

I think with all the new changes, this issue is no longer relevant. Thanks!