bevy_ecs/system/
combinator.rs

1use alloc::borrow::Cow;
2use core::marker::PhantomData;
3
4use crate::{
5    archetype::ArchetypeComponentId,
6    component::{ComponentId, Tick},
7    prelude::World,
8    query::Access,
9    schedule::InternedSystemSet,
10    system::{input::SystemInput, SystemIn},
11    world::unsafe_world_cell::UnsafeWorldCell,
12};
13
14use super::{IntoSystem, ReadOnlySystem, System};
15
16/// Customizes the behavior of a [`CombinatorSystem`].
17///
18/// # Examples
19///
20/// ```
21/// use bevy_ecs::prelude::*;
22/// use bevy_ecs::system::{CombinatorSystem, Combine};
23///
24/// // A system combinator that performs an exclusive-or (XOR)
25/// // operation on the output of two systems.
26/// pub type Xor<A, B> = CombinatorSystem<XorMarker, A, B>;
27///
28/// // This struct is used to customize the behavior of our combinator.
29/// pub struct XorMarker;
30///
31/// impl<A, B> Combine<A, B> for XorMarker
32/// where
33///     A: System<In = (), Out = bool>,
34///     B: System<In = (), Out = bool>,
35/// {
36///     type In = ();
37///     type Out = bool;
38///
39///     fn combine(
40///         _input: Self::In,
41///         a: impl FnOnce(A::In) -> A::Out,
42///         b: impl FnOnce(B::In) -> B::Out,
43///     ) -> Self::Out {
44///         a(()) ^ b(())
45///     }
46/// }
47///
48/// # #[derive(Resource, PartialEq, Eq)] struct A(u32);
49/// # #[derive(Resource, PartialEq, Eq)] struct B(u32);
50/// # #[derive(Resource, Default)] struct RanFlag(bool);
51/// # let mut world = World::new();
52/// # world.init_resource::<RanFlag>();
53/// #
54/// # let mut app = Schedule::default();
55/// app.add_systems(my_system.run_if(Xor::new(
56///     IntoSystem::into_system(resource_equals(A(1))),
57///     IntoSystem::into_system(resource_equals(B(1))),
58///     // The name of the combined system.
59///     std::borrow::Cow::Borrowed("a ^ b"),
60/// )));
61/// # fn my_system(mut flag: ResMut<RanFlag>) { flag.0 = true; }
62/// #
63/// # world.insert_resource(A(0));
64/// # world.insert_resource(B(0));
65/// # app.run(&mut world);
66/// # // Neither condition passes, so the system does not run.
67/// # assert!(!world.resource::<RanFlag>().0);
68/// #
69/// # world.insert_resource(A(1));
70/// # app.run(&mut world);
71/// # // Only the first condition passes, so the system runs.
72/// # assert!(world.resource::<RanFlag>().0);
73/// # world.resource_mut::<RanFlag>().0 = false;
74/// #
75/// # world.insert_resource(B(1));
76/// # app.run(&mut world);
77/// # // Both conditions pass, so the system does not run.
78/// # assert!(!world.resource::<RanFlag>().0);
79/// #
80/// # world.insert_resource(A(0));
81/// # app.run(&mut world);
82/// # // Only the second condition passes, so the system runs.
83/// # assert!(world.resource::<RanFlag>().0);
84/// # world.resource_mut::<RanFlag>().0 = false;
85/// ```
86#[diagnostic::on_unimplemented(
87    message = "`{Self}` can not combine systems `{A}` and `{B}`",
88    label = "invalid system combination",
89    note = "the inputs and outputs of `{A}` and `{B}` are not compatible with this combiner"
90)]
91pub trait Combine<A: System, B: System> {
92    /// The [input](System::In) type for a [`CombinatorSystem`].
93    type In: SystemInput;
94
95    /// The [output](System::Out) type for a [`CombinatorSystem`].
96    type Out;
97
98    /// When used in a [`CombinatorSystem`], this function customizes how
99    /// the two composite systems are invoked and their outputs are combined.
100    ///
101    /// See the trait-level docs for [`Combine`] for an example implementation.
102    fn combine(
103        input: <Self::In as SystemInput>::Inner<'_>,
104        a: impl FnOnce(SystemIn<'_, A>) -> A::Out,
105        b: impl FnOnce(SystemIn<'_, B>) -> B::Out,
106    ) -> Self::Out;
107}
108
109/// A [`System`] defined by combining two other systems.
110/// The behavior of this combinator is specified by implementing the [`Combine`] trait.
111/// For a full usage example, see the docs for [`Combine`].
112pub struct CombinatorSystem<Func, A, B> {
113    _marker: PhantomData<fn() -> Func>,
114    a: A,
115    b: B,
116    name: Cow<'static, str>,
117    component_access: Access<ComponentId>,
118    archetype_component_access: Access<ArchetypeComponentId>,
119}
120
121impl<Func, A, B> CombinatorSystem<Func, A, B> {
122    /// Creates a new system that combines two inner systems.
123    ///
124    /// The returned system will only be usable if `Func` implements [`Combine<A, B>`].
125    pub const fn new(a: A, b: B, name: Cow<'static, str>) -> Self {
126        Self {
127            _marker: PhantomData,
128            a,
129            b,
130            name,
131            component_access: Access::new(),
132            archetype_component_access: Access::new(),
133        }
134    }
135}
136
137impl<A, B, Func> System for CombinatorSystem<Func, A, B>
138where
139    Func: Combine<A, B> + 'static,
140    A: System,
141    B: System,
142{
143    type In = Func::In;
144    type Out = Func::Out;
145
146    fn name(&self) -> Cow<'static, str> {
147        self.name.clone()
148    }
149
150    fn component_access(&self) -> &Access<ComponentId> {
151        &self.component_access
152    }
153
154    fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
155        &self.archetype_component_access
156    }
157
158    fn is_send(&self) -> bool {
159        self.a.is_send() && self.b.is_send()
160    }
161
162    fn is_exclusive(&self) -> bool {
163        self.a.is_exclusive() || self.b.is_exclusive()
164    }
165
166    fn has_deferred(&self) -> bool {
167        self.a.has_deferred() || self.b.has_deferred()
168    }
169
170    unsafe fn run_unsafe(
171        &mut self,
172        input: SystemIn<'_, Self>,
173        world: UnsafeWorldCell,
174    ) -> Self::Out {
175        Func::combine(
176            input,
177            // SAFETY: The world accesses for both underlying systems have been registered,
178            // so the caller will guarantee that no other systems will conflict with `a` or `b`.
179            // Since these closures are `!Send + !Sync + !'static`, they can never be called
180            // in parallel, so their world accesses will not conflict with each other.
181            // Additionally, `update_archetype_component_access` has been called,
182            // which forwards to the implementations for `self.a` and `self.b`.
183            |input| unsafe { self.a.run_unsafe(input, world) },
184            // SAFETY: See the comment above.
185            |input| unsafe { self.b.run_unsafe(input, world) },
186        )
187    }
188
189    fn run(&mut self, input: SystemIn<'_, Self>, world: &mut World) -> Self::Out {
190        let world = world.as_unsafe_world_cell();
191        Func::combine(
192            input,
193            // SAFETY: Since these closures are `!Send + !Sync + !'static`, they can never
194            // be called in parallel. Since mutable access to `world` only exists within
195            // the scope of either closure, we can be sure they will never alias one another.
196            |input| self.a.run(input, unsafe { world.world_mut() }),
197            #[allow(clippy::undocumented_unsafe_blocks)]
198            |input| self.b.run(input, unsafe { world.world_mut() }),
199        )
200    }
201
202    #[inline]
203    fn apply_deferred(&mut self, world: &mut World) {
204        self.a.apply_deferred(world);
205        self.b.apply_deferred(world);
206    }
207
208    #[inline]
209    fn queue_deferred(&mut self, mut world: crate::world::DeferredWorld) {
210        self.a.queue_deferred(world.reborrow());
211        self.b.queue_deferred(world);
212    }
213
214    #[inline]
215    unsafe fn validate_param_unsafe(&mut self, world: UnsafeWorldCell) -> bool {
216        // SAFETY: Delegate to other `System` implementations.
217        unsafe { self.a.validate_param_unsafe(world) }
218    }
219
220    fn initialize(&mut self, world: &mut World) {
221        self.a.initialize(world);
222        self.b.initialize(world);
223        self.component_access.extend(self.a.component_access());
224        self.component_access.extend(self.b.component_access());
225    }
226
227    fn update_archetype_component_access(&mut self, world: UnsafeWorldCell) {
228        self.a.update_archetype_component_access(world);
229        self.b.update_archetype_component_access(world);
230
231        self.archetype_component_access
232            .extend(self.a.archetype_component_access());
233        self.archetype_component_access
234            .extend(self.b.archetype_component_access());
235    }
236
237    fn check_change_tick(&mut self, change_tick: Tick) {
238        self.a.check_change_tick(change_tick);
239        self.b.check_change_tick(change_tick);
240    }
241
242    fn default_system_sets(&self) -> Vec<InternedSystemSet> {
243        let mut default_sets = self.a.default_system_sets();
244        default_sets.append(&mut self.b.default_system_sets());
245        default_sets
246    }
247
248    fn get_last_run(&self) -> Tick {
249        self.a.get_last_run()
250    }
251
252    fn set_last_run(&mut self, last_run: Tick) {
253        self.a.set_last_run(last_run);
254        self.b.set_last_run(last_run);
255    }
256}
257
258/// SAFETY: Both systems are read-only, so any system created by combining them will only read from the world.
259unsafe impl<Func, A, B> ReadOnlySystem for CombinatorSystem<Func, A, B>
260where
261    Func: Combine<A, B> + 'static,
262    A: ReadOnlySystem,
263    B: ReadOnlySystem,
264{
265}
266
267impl<Func, A, B> Clone for CombinatorSystem<Func, A, B>
268where
269    A: Clone,
270    B: Clone,
271{
272    /// Clone the combined system. The cloned instance must be `.initialize()`d before it can run.
273    fn clone(&self) -> Self {
274        CombinatorSystem::new(self.a.clone(), self.b.clone(), self.name.clone())
275    }
276}
277
278/// An [`IntoSystem`] creating an instance of [`PipeSystem`].
279pub struct IntoPipeSystem<A, B> {
280    a: A,
281    b: B,
282}
283
284impl<A, B> IntoPipeSystem<A, B> {
285    /// Creates a new [`IntoSystem`] that pipes two inner systems.
286    pub const fn new(a: A, b: B) -> Self {
287        Self { a, b }
288    }
289}
290
291#[doc(hidden)]
292pub struct IsPipeSystemMarker;
293
294impl<A, B, IA, OA, IB, OB, MA, MB> IntoSystem<IA, OB, (IsPipeSystemMarker, OA, IB, MA, MB)>
295    for IntoPipeSystem<A, B>
296where
297    IA: SystemInput,
298    A: IntoSystem<IA, OA, MA>,
299    B: IntoSystem<IB, OB, MB>,
300    for<'a> IB: SystemInput<Inner<'a> = OA>,
301{
302    type System = PipeSystem<A::System, B::System>;
303
304    fn into_system(this: Self) -> Self::System {
305        let system_a = IntoSystem::into_system(this.a);
306        let system_b = IntoSystem::into_system(this.b);
307        let name = format!("Pipe({}, {})", system_a.name(), system_b.name());
308        PipeSystem::new(system_a, system_b, Cow::Owned(name))
309    }
310}
311
312/// A [`System`] created by piping the output of the first system into the input of the second.
313///
314/// This can be repeated indefinitely, but system pipes cannot branch: the output is consumed by the receiving system.
315///
316/// Given two systems `A` and `B`, A may be piped into `B` as `A.pipe(B)` if the output type of `A` is
317/// equal to the input type of `B`.
318///
319/// Note that for [`FunctionSystem`](crate::system::FunctionSystem)s the output is the return value
320/// of the function and the input is the first [`SystemParam`](crate::system::SystemParam) if it is
321/// tagged with [`In`](crate::system::In) or `()` if the function has no designated input parameter.
322///
323/// # Examples
324///
325/// ```
326/// use std::num::ParseIntError;
327///
328/// use bevy_ecs::prelude::*;
329///
330/// fn main() {
331///     let mut world = World::default();
332///     world.insert_resource(Message("42".to_string()));
333///
334///     // pipe the `parse_message_system`'s output into the `filter_system`s input
335///     let mut piped_system = IntoSystem::into_system(parse_message_system.pipe(filter_system));
336///     piped_system.initialize(&mut world);
337///     assert_eq!(piped_system.run((), &mut world), Some(42));
338/// }
339///
340/// #[derive(Resource)]
341/// struct Message(String);
342///
343/// fn parse_message_system(message: Res<Message>) -> Result<usize, ParseIntError> {
344///     message.0.parse::<usize>()
345/// }
346///
347/// fn filter_system(In(result): In<Result<usize, ParseIntError>>) -> Option<usize> {
348///     result.ok().filter(|&n| n < 100)
349/// }
350/// ```
351pub struct PipeSystem<A, B> {
352    a: A,
353    b: B,
354    name: Cow<'static, str>,
355    component_access: Access<ComponentId>,
356    archetype_component_access: Access<ArchetypeComponentId>,
357}
358
359impl<A, B> PipeSystem<A, B>
360where
361    A: System,
362    B: System,
363    for<'a> B::In: SystemInput<Inner<'a> = A::Out>,
364{
365    /// Creates a new system that pipes two inner systems.
366    pub const fn new(a: A, b: B, name: Cow<'static, str>) -> Self {
367        Self {
368            a,
369            b,
370            name,
371            component_access: Access::new(),
372            archetype_component_access: Access::new(),
373        }
374    }
375}
376
377impl<A, B> System for PipeSystem<A, B>
378where
379    A: System,
380    B: System,
381    for<'a> B::In: SystemInput<Inner<'a> = A::Out>,
382{
383    type In = A::In;
384    type Out = B::Out;
385
386    fn name(&self) -> Cow<'static, str> {
387        self.name.clone()
388    }
389
390    fn component_access(&self) -> &Access<ComponentId> {
391        &self.component_access
392    }
393
394    fn archetype_component_access(&self) -> &Access<ArchetypeComponentId> {
395        &self.archetype_component_access
396    }
397
398    fn is_send(&self) -> bool {
399        self.a.is_send() && self.b.is_send()
400    }
401
402    fn is_exclusive(&self) -> bool {
403        self.a.is_exclusive() || self.b.is_exclusive()
404    }
405
406    fn has_deferred(&self) -> bool {
407        self.a.has_deferred() || self.b.has_deferred()
408    }
409
410    unsafe fn run_unsafe(
411        &mut self,
412        input: SystemIn<'_, Self>,
413        world: UnsafeWorldCell,
414    ) -> Self::Out {
415        let value = self.a.run_unsafe(input, world);
416        self.b.run_unsafe(value, world)
417    }
418
419    fn run(&mut self, input: SystemIn<'_, Self>, world: &mut World) -> Self::Out {
420        let value = self.a.run(input, world);
421        self.b.run(value, world)
422    }
423
424    fn apply_deferred(&mut self, world: &mut World) {
425        self.a.apply_deferred(world);
426        self.b.apply_deferred(world);
427    }
428
429    fn queue_deferred(&mut self, mut world: crate::world::DeferredWorld) {
430        self.a.queue_deferred(world.reborrow());
431        self.b.queue_deferred(world);
432    }
433
434    unsafe fn validate_param_unsafe(&mut self, world: UnsafeWorldCell) -> bool {
435        // SAFETY: Delegate to other `System` implementations.
436        unsafe { self.a.validate_param_unsafe(world) }
437    }
438
439    fn validate_param(&mut self, world: &World) -> bool {
440        self.a.validate_param(world) && self.b.validate_param(world)
441    }
442
443    fn initialize(&mut self, world: &mut World) {
444        self.a.initialize(world);
445        self.b.initialize(world);
446        self.component_access.extend(self.a.component_access());
447        self.component_access.extend(self.b.component_access());
448    }
449
450    fn update_archetype_component_access(&mut self, world: UnsafeWorldCell) {
451        self.a.update_archetype_component_access(world);
452        self.b.update_archetype_component_access(world);
453
454        self.archetype_component_access
455            .extend(self.a.archetype_component_access());
456        self.archetype_component_access
457            .extend(self.b.archetype_component_access());
458    }
459
460    fn check_change_tick(&mut self, change_tick: Tick) {
461        self.a.check_change_tick(change_tick);
462        self.b.check_change_tick(change_tick);
463    }
464
465    fn default_system_sets(&self) -> Vec<InternedSystemSet> {
466        let mut default_sets = self.a.default_system_sets();
467        default_sets.append(&mut self.b.default_system_sets());
468        default_sets
469    }
470
471    fn get_last_run(&self) -> Tick {
472        self.a.get_last_run()
473    }
474
475    fn set_last_run(&mut self, last_run: Tick) {
476        self.a.set_last_run(last_run);
477        self.b.set_last_run(last_run);
478    }
479}
480
481/// SAFETY: Both systems are read-only, so any system created by piping them will only read from the world.
482unsafe impl<A, B> ReadOnlySystem for PipeSystem<A, B>
483where
484    A: ReadOnlySystem,
485    B: ReadOnlySystem,
486    for<'a> B::In: SystemInput<Inner<'a> = A::Out>,
487{
488}
bevy_ecs/system/combinator.rs

bevy_ecs/system/
combinator.rs
