bevy_ecs/system/
exclusive_system_param.rs

1use crate::{
2    prelude::{FromWorld, QueryState},
3    query::{QueryData, QueryFilter},
4    system::{Local, SystemMeta, SystemParam, SystemState},
5    world::World,
6};
7use bevy_utils::synccell::SyncCell;
8use core::marker::PhantomData;
9use variadics_please::all_tuples;
10
11/// A parameter that can be used in an exclusive system (a system with an `&mut World` parameter).
12/// Any parameters implementing this trait must come after the `&mut World` parameter.
13#[diagnostic::on_unimplemented(
14    message = "`{Self}` can not be used as a parameter for an exclusive system",
15    label = "invalid system parameter"
16)]
17pub trait ExclusiveSystemParam: Sized {
18    /// Used to store data which persists across invocations of a system.
19    type State: Send + Sync + 'static;
20    /// The item type returned when constructing this system param.
21    /// See [`SystemParam::Item`].
22    type Item<'s>: ExclusiveSystemParam<State = Self::State>;
23
24    /// Creates a new instance of this param's [`State`](Self::State).
25    fn init(world: &mut World, system_meta: &mut SystemMeta) -> Self::State;
26
27    /// Creates a parameter to be passed into an [`ExclusiveSystemParamFunction`].
28    ///
29    /// [`ExclusiveSystemParamFunction`]: super::ExclusiveSystemParamFunction
30    fn get_param<'s>(state: &'s mut Self::State, system_meta: &SystemMeta) -> Self::Item<'s>;
31}
32
33/// Shorthand way of accessing the associated type [`ExclusiveSystemParam::Item`]
34/// for a given [`ExclusiveSystemParam`].
35pub type ExclusiveSystemParamItem<'s, P> = <P as ExclusiveSystemParam>::Item<'s>;
36
37impl<'a, D: QueryData + 'static, F: QueryFilter + 'static> ExclusiveSystemParam
38    for &'a mut QueryState<D, F>
39{
40    type State = QueryState<D, F>;
41    type Item<'s> = &'s mut QueryState<D, F>;
42
43    fn init(world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
44        QueryState::new(world)
45    }
46
47    fn get_param<'s>(state: &'s mut Self::State, _system_meta: &SystemMeta) -> Self::Item<'s> {
48        state
49    }
50}
51
52impl<'a, P: SystemParam + 'static> ExclusiveSystemParam for &'a mut SystemState<P> {
53    type State = SystemState<P>;
54    type Item<'s> = &'s mut SystemState<P>;
55
56    fn init(world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
57        SystemState::new(world)
58    }
59
60    fn get_param<'s>(state: &'s mut Self::State, _system_meta: &SystemMeta) -> Self::Item<'s> {
61        state
62    }
63}
64
65impl<'_s, T: FromWorld + Send + 'static> ExclusiveSystemParam for Local<'_s, T> {
66    type State = SyncCell<T>;
67    type Item<'s> = Local<'s, T>;
68
69    fn init(world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
70        SyncCell::new(T::from_world(world))
71    }
72
73    fn get_param<'s>(state: &'s mut Self::State, _system_meta: &SystemMeta) -> Self::Item<'s> {
74        Local(state.get())
75    }
76}
77
78impl<S: ?Sized> ExclusiveSystemParam for PhantomData<S> {
79    type State = ();
80    type Item<'s> = PhantomData<S>;
81
82    fn init(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
83
84    fn get_param<'s>(_state: &'s mut Self::State, _system_meta: &SystemMeta) -> Self::Item<'s> {
85        PhantomData
86    }
87}
88
89macro_rules! impl_exclusive_system_param_tuple {
90    ($(#[$meta:meta])* $($param: ident),*) => {
91        #[expect(
92            clippy::allow_attributes,
93            reason = "This is within a macro, and as such, the below lints may not always apply."
94        )]
95        #[allow(
96            non_snake_case,
97            reason = "Certain variable names are provided by the caller, not by us."
98        )]
99        #[allow(
100            unused_variables,
101            reason = "Zero-length tuples won't use any of the parameters."
102        )]
103        $(#[$meta])*
104        impl<$($param: ExclusiveSystemParam),*> ExclusiveSystemParam for ($($param,)*) {
105            type State = ($($param::State,)*);
106            type Item<'s> = ($($param::Item<'s>,)*);
107
108            #[inline]
109            fn init(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
110                (($($param::init(world, system_meta),)*))
111            }
112
113            #[inline]
114            fn get_param<'s>(
115                state: &'s mut Self::State,
116                system_meta: &SystemMeta,
117            ) -> Self::Item<'s> {
118                let ($($param,)*) = state;
119                #[allow(
120                    clippy::unused_unit,
121                    reason = "Zero-length tuples won't have any params to get."
122                )]
123                ($($param::get_param($param, system_meta),)*)
124            }
125        }
126    };
127}
128
129all_tuples!(
130    #[doc(fake_variadic)]
131    impl_exclusive_system_param_tuple,
132    0,
133    16,
134    P
135);
136
137#[cfg(test)]
138mod tests {
139    use crate::{schedule::Schedule, system::Local, world::World};
140    use alloc::vec::Vec;
141    use bevy_ecs_macros::Resource;
142    use core::marker::PhantomData;
143
144    #[test]
145    fn test_exclusive_system_params() {
146        #[derive(Resource, Default)]
147        struct Res {
148            test_value: u32,
149        }
150
151        fn my_system(world: &mut World, mut local: Local<u32>, _phantom: PhantomData<Vec<u32>>) {
152            assert_eq!(world.resource::<Res>().test_value, *local);
153            *local += 1;
154            world.resource_mut::<Res>().test_value += 1;
155        }
156
157        let mut schedule = Schedule::default();
158        schedule.add_systems(my_system);
159
160        let mut world = World::default();
161        world.init_resource::<Res>();
162
163        schedule.run(&mut world);
164        schedule.run(&mut world);
165
166        assert_eq!(2, world.get_resource::<Res>().unwrap().test_value);
167    }
168}
bevy_ecs/system/exclusive_system_param.rs

bevy_ecs/system/
exclusive_system_param.rs
