Macro define_system

macro_rules! define_system {
    (/param_defs/ $table:ident / $func_body:block / |$param_name:ident: $param_type:ty|) => { ... };
    (/param_defs/ $table:ident / $func_body:block / |$param_name:ident: $param_type:ty, $($rest_names:ident: $rest_types:ty),+|) => { ... };
    (|$handle_name:pat_param, $($param_name:ident: $param_type:ty),+| $func_body:block) => { ... };
}

Gutputs a closure that can be passed into Scene::run_system, handling extracting properly typed component columns based on the parameter list.

The GameObjectHandleIterator parameter from Scene::run_system is always assigned to first parameter of the closure.

The generated closure extracts the relevant component slices from the anonymous ComponentColumns, and makes them available to the closure body as variables, using the names from the parameter list.

For simplicity, the parameters after the first one can only be mutable slices, but note that Scene::run_system takes a FnMut, so the closure can borrow and even mutate their captured environment.

Example

let mut game_object_handle = None;
scene.run_system(define_system!(|handles, pos: &mut [Position], vel: &[Velocity]| {
    for ((handle, pos), vel) in handles.zip(pos).zip(vel) {
        pos.x += vel.x;
        pos.y += vel.y;
        game_object_handle = Some(handle);
    }
}));
if let Some(handle) = game_object_handle {
    scene.delete(&mut [handle]).unwrap();
}