bevy_ecs/reflect/
component.rs

1//! Definitions for [`Component`] reflection.
2//! This allows inserting, updating, removing and generally interacting with components
3//! whose types are only known at runtime.
4//!
5//! This module exports two types: [`ReflectComponentFns`] and [`ReflectComponent`].
6//!
7//! # Architecture
8//!
9//! [`ReflectComponent`] wraps a [`ReflectComponentFns`]. In fact, each method on
10//! [`ReflectComponent`] wraps a call to a function pointer field in `ReflectComponentFns`.
11//!
12//! ## Who creates `ReflectComponent`s?
13//!
14//! When a user adds the `#[reflect(Component)]` attribute to their `#[derive(Reflect)]`
15//! type, it tells the derive macro for `Reflect` to add the following single line to its
16//! [`get_type_registration`] method (see the relevant code[^1]).
17//!
18//! ```
19//! # use bevy_reflect::{FromType, Reflect};
20//! # use bevy_ecs::prelude::{ReflectComponent, Component};
21//! # #[derive(Default, Reflect, Component)]
22//! # struct A;
23//! # impl A {
24//! #   fn foo() {
25//! # let mut registration = bevy_reflect::TypeRegistration::of::<A>();
26//! registration.insert::<ReflectComponent>(FromType::<Self>::from_type());
27//! #   }
28//! # }
29//! ```
30//!
31//! This line adds a `ReflectComponent` to the registration data for the type in question.
32//! The user can access the `ReflectComponent` for type `T` through the type registry,
33//! as per the `trait_reflection.rs` example.
34//!
35//! The `FromType::<Self>::from_type()` in the previous line calls the `FromType<C>`
36//! implementation of `ReflectComponent`.
37//!
38//! The `FromType<C>` impl creates a function per field of [`ReflectComponentFns`].
39//! In those functions, we call generic methods on [`World`] and [`EntityWorldMut`].
40//!
41//! The result is a `ReflectComponent` completely independent of `C`, yet capable
42//! of using generic ECS methods such as `entity.get::<C>()` to get `&dyn Reflect`
43//! with underlying type `C`, without the `C` appearing in the type signature.
44//!
45//! ## A note on code generation
46//!
47//! A downside of this approach is that monomorphized code (ie: concrete code
48//! for generics) is generated **unconditionally**, regardless of whether it ends
49//! up used or not.
50//!
51//! Adding `N` fields on `ReflectComponentFns` will generate `N × M` additional
52//! functions, where `M` is how many types derive `#[reflect(Component)]`.
53//!
54//! Those functions will increase the size of the final app binary.
55//!
56//! [^1]: `crates/bevy_reflect/bevy_reflect_derive/src/registration.rs`
57//!
58//! [`get_type_registration`]: bevy_reflect::GetTypeRegistration::get_type_registration
59
60use super::from_reflect_with_fallback;
61use crate::{
62    change_detection::Mut,
63    component::{ComponentId, ComponentMutability},
64    entity::{Entity, EntityMapper},
65    prelude::Component,
66    relationship::RelationshipHookMode,
67    world::{
68        unsafe_world_cell::UnsafeEntityCell, EntityMut, EntityWorldMut, FilteredEntityMut,
69        FilteredEntityRef, World,
70    },
71};
72use bevy_reflect::{FromReflect, FromType, PartialReflect, Reflect, TypePath, TypeRegistry};
73use bevy_utils::prelude::DebugName;
74
75/// A struct used to operate on reflected [`Component`] trait of a type.
76///
77/// A [`ReflectComponent`] for type `T` can be obtained via
78/// [`bevy_reflect::TypeRegistration::data`].
79#[derive(Clone)]
80pub struct ReflectComponent(ReflectComponentFns);
81
82/// The raw function pointers needed to make up a [`ReflectComponent`].
83///
84/// This is used when creating custom implementations of [`ReflectComponent`] with
85/// [`ReflectComponent::new()`].
86///
87/// > **Note:**
88/// > Creating custom implementations of [`ReflectComponent`] is an advanced feature that most users
89/// > will not need.
90/// > Usually a [`ReflectComponent`] is created for a type by deriving [`Reflect`]
91/// > and adding the `#[reflect(Component)]` attribute.
92/// > After adding the component to the [`TypeRegistry`],
93/// > its [`ReflectComponent`] can then be retrieved when needed.
94///
95/// Creating a custom [`ReflectComponent`] may be useful if you need to create new component types
96/// at runtime, for example, for scripting implementations.
97///
98/// By creating a custom [`ReflectComponent`] and inserting it into a type's
99/// [`TypeRegistration`][bevy_reflect::TypeRegistration],
100/// you can modify the way that reflected components of that type will be inserted into the Bevy
101/// world.
102#[derive(Clone)]
103pub struct ReflectComponentFns {
104    /// Function pointer implementing [`ReflectComponent::insert()`].
105    pub insert: fn(&mut EntityWorldMut, &dyn PartialReflect, &TypeRegistry),
106    /// Function pointer implementing [`ReflectComponent::apply()`].
107    pub apply: fn(EntityMut, &dyn PartialReflect),
108    /// Function pointer implementing [`ReflectComponent::apply_or_insert_mapped()`].
109    pub apply_or_insert_mapped: fn(
110        &mut EntityWorldMut,
111        &dyn PartialReflect,
112        &TypeRegistry,
113        &mut dyn EntityMapper,
114        RelationshipHookMode,
115    ),
116    /// Function pointer implementing [`ReflectComponent::remove()`].
117    pub remove: fn(&mut EntityWorldMut),
118    /// Function pointer implementing [`ReflectComponent::contains()`].
119    pub contains: fn(FilteredEntityRef) -> bool,
120    /// Function pointer implementing [`ReflectComponent::reflect()`].
121    pub reflect: for<'w> fn(FilteredEntityRef<'w, '_>) -> Option<&'w dyn Reflect>,
122    /// Function pointer implementing [`ReflectComponent::reflect_mut()`].
123    pub reflect_mut: for<'w> fn(FilteredEntityMut<'w, '_>) -> Option<Mut<'w, dyn Reflect>>,
124    /// Function pointer implementing [`ReflectComponent::map_entities()`].
125    pub map_entities: fn(&mut dyn Reflect, &mut dyn EntityMapper),
126    /// Function pointer implementing [`ReflectComponent::reflect_unchecked_mut()`].
127    ///
128    /// # Safety
129    /// The function may only be called with an [`UnsafeEntityCell`] that can be used to mutably access the relevant component on the given entity.
130    pub reflect_unchecked_mut: unsafe fn(UnsafeEntityCell<'_>) -> Option<Mut<'_, dyn Reflect>>,
131    /// Function pointer implementing [`ReflectComponent::copy()`].
132    pub copy: fn(&World, &mut World, Entity, Entity, &TypeRegistry),
133    /// Function pointer implementing [`ReflectComponent::register_component()`].
134    pub register_component: fn(&mut World) -> ComponentId,
135}
136
137impl ReflectComponentFns {
138    /// Get the default set of [`ReflectComponentFns`] for a specific component type using its
139    /// [`FromType`] implementation.
140    ///
141    /// This is useful if you want to start with the default implementation before overriding some
142    /// of the functions to create a custom implementation.
143    pub fn new<T: Component + FromReflect + TypePath>() -> Self {
144        <ReflectComponent as FromType<T>>::from_type().0
145    }
146}
147
148impl ReflectComponent {
149    /// Insert a reflected [`Component`] into the entity like [`insert()`](EntityWorldMut::insert).
150    pub fn insert(
151        &self,
152        entity: &mut EntityWorldMut,
153        component: &dyn PartialReflect,
154        registry: &TypeRegistry,
155    ) {
156        (self.0.insert)(entity, component, registry);
157    }
158
159    /// Uses reflection to set the value of this [`Component`] type in the entity to the given value.
160    ///
161    /// # Panics
162    ///
163    /// Panics if there is no [`Component`] of the given type.
164    ///
165    /// Will also panic if [`Component`] is immutable.
166    pub fn apply<'a>(&self, entity: impl Into<EntityMut<'a>>, component: &dyn PartialReflect) {
167        (self.0.apply)(entity.into(), component);
168    }
169
170    /// Uses reflection to set the value of this [`Component`] type in the entity to the given value or insert a new one if it does not exist.
171    ///
172    /// # Panics
173    ///
174    /// Panics if [`Component`] is immutable.
175    pub fn apply_or_insert_mapped(
176        &self,
177        entity: &mut EntityWorldMut,
178        component: &dyn PartialReflect,
179        registry: &TypeRegistry,
180        map: &mut dyn EntityMapper,
181        relationship_hook_mode: RelationshipHookMode,
182    ) {
183        (self.0.apply_or_insert_mapped)(entity, component, registry, map, relationship_hook_mode);
184    }
185
186    /// Removes this [`Component`] type from the entity. Does nothing if it doesn't exist.
187    pub fn remove(&self, entity: &mut EntityWorldMut) {
188        (self.0.remove)(entity);
189    }
190
191    /// Returns whether entity contains this [`Component`]
192    pub fn contains<'w, 's>(&self, entity: impl Into<FilteredEntityRef<'w, 's>>) -> bool {
193        (self.0.contains)(entity.into())
194    }
195
196    /// Gets the value of this [`Component`] type from the entity as a reflected reference.
197    pub fn reflect<'w, 's>(
198        &self,
199        entity: impl Into<FilteredEntityRef<'w, 's>>,
200    ) -> Option<&'w dyn Reflect> {
201        (self.0.reflect)(entity.into())
202    }
203
204    /// Gets the value of this [`Component`] type from the entity as a mutable reflected reference.
205    ///
206    /// # Panics
207    ///
208    /// Panics if [`Component`] is immutable.
209    pub fn reflect_mut<'w, 's>(
210        &self,
211        entity: impl Into<FilteredEntityMut<'w, 's>>,
212    ) -> Option<Mut<'w, dyn Reflect>> {
213        (self.0.reflect_mut)(entity.into())
214    }
215
216    /// # Safety
217    /// This method does not prevent you from having two mutable pointers to the same data,
218    /// violating Rust's aliasing rules. To avoid this:
219    /// * Only call this method with a [`UnsafeEntityCell`] that may be used to mutably access the component on the entity `entity`
220    /// * Don't call this method more than once in the same scope for a given [`Component`].
221    ///
222    /// # Panics
223    ///
224    /// Panics if [`Component`] is immutable.
225    pub unsafe fn reflect_unchecked_mut<'a>(
226        &self,
227        entity: UnsafeEntityCell<'a>,
228    ) -> Option<Mut<'a, dyn Reflect>> {
229        // SAFETY: safety requirements deferred to caller
230        unsafe { (self.0.reflect_unchecked_mut)(entity) }
231    }
232
233    /// Gets the value of this [`Component`] type from entity from `source_world` and [applies](Self::apply()) it to the value of this [`Component`] type in entity in `destination_world`.
234    ///
235    /// # Panics
236    ///
237    /// Panics if there is no [`Component`] of the given type or either entity does not exist.
238    pub fn copy(
239        &self,
240        source_world: &World,
241        destination_world: &mut World,
242        source_entity: Entity,
243        destination_entity: Entity,
244        registry: &TypeRegistry,
245    ) {
246        (self.0.copy)(
247            source_world,
248            destination_world,
249            source_entity,
250            destination_entity,
251            registry,
252        );
253    }
254
255    /// Register the type of this [`Component`] in [`World`], returning its [`ComponentId`].
256    pub fn register_component(&self, world: &mut World) -> ComponentId {
257        (self.0.register_component)(world)
258    }
259
260    /// Create a custom implementation of [`ReflectComponent`].
261    ///
262    /// This is an advanced feature,
263    /// useful for scripting implementations,
264    /// that should not be used by most users
265    /// unless you know what you are doing.
266    ///
267    /// Usually you should derive [`Reflect`] and add the `#[reflect(Component)]` component
268    /// to generate a [`ReflectComponent`] implementation automatically.
269    ///
270    /// See [`ReflectComponentFns`] for more information.
271    pub fn new(fns: ReflectComponentFns) -> Self {
272        Self(fns)
273    }
274
275    /// The underlying function pointers implementing methods on `ReflectComponent`.
276    ///
277    /// This is useful when you want to keep track locally of an individual
278    /// function pointer.
279    ///
280    /// Calling [`TypeRegistry::get`] followed by
281    /// [`TypeRegistration::data::<ReflectComponent>`] can be costly if done several
282    /// times per frame. Consider cloning [`ReflectComponent`] and keeping it
283    /// between frames, cloning a `ReflectComponent` is very cheap.
284    ///
285    /// If you only need a subset of the methods on `ReflectComponent`,
286    /// use `fn_pointers` to get the underlying [`ReflectComponentFns`]
287    /// and copy the subset of function pointers you care about.
288    ///
289    /// [`TypeRegistration::data::<ReflectComponent>`]: bevy_reflect::TypeRegistration::data
290    /// [`TypeRegistry::get`]: bevy_reflect::TypeRegistry::get
291    pub fn fn_pointers(&self) -> &ReflectComponentFns {
292        &self.0
293    }
294
295    /// Calls a dynamic version of [`Component::map_entities`].
296    pub fn map_entities(&self, component: &mut dyn Reflect, func: &mut dyn EntityMapper) {
297        (self.0.map_entities)(component, func);
298    }
299}
300
301impl<C: Component + Reflect + TypePath> FromType<C> for ReflectComponent {
302    fn from_type() -> Self {
303        // TODO: Currently we panic if a component is immutable and you use
304        // reflection to mutate it. Perhaps the mutation methods should be fallible?
305        ReflectComponent(ReflectComponentFns {
306            insert: |entity, reflected_component, registry| {
307                let component = entity.world_scope(|world| {
308                    from_reflect_with_fallback::<C>(reflected_component, world, registry)
309                });
310                entity.insert(component);
311            },
312            apply: |mut entity, reflected_component| {
313                if !C::Mutability::MUTABLE {
314                    let name = DebugName::type_name::<C>();
315                    let name = name.shortname();
316                    panic!("Cannot call `ReflectComponent::apply` on component {name}. It is immutable, and cannot modified through reflection");
317                }
318
319                // SAFETY: guard ensures `C` is a mutable component
320                let mut component = unsafe { entity.get_mut_assume_mutable::<C>() }.unwrap();
321                component.apply(reflected_component);
322            },
323            apply_or_insert_mapped: |entity,
324                                     reflected_component,
325                                     registry,
326                                     mut mapper,
327                                     relationship_hook_mode| {
328                if C::Mutability::MUTABLE {
329                    // SAFETY: guard ensures `C` is a mutable component
330                    if let Some(mut component) = unsafe { entity.get_mut_assume_mutable::<C>() } {
331                        component.apply(reflected_component.as_partial_reflect());
332                        C::map_entities(&mut component, &mut mapper);
333                    } else {
334                        let mut component = entity.world_scope(|world| {
335                            from_reflect_with_fallback::<C>(reflected_component, world, registry)
336                        });
337                        C::map_entities(&mut component, &mut mapper);
338                        entity
339                            .insert_with_relationship_hook_mode(component, relationship_hook_mode);
340                    }
341                } else {
342                    let mut component = entity.world_scope(|world| {
343                        from_reflect_with_fallback::<C>(reflected_component, world, registry)
344                    });
345                    C::map_entities(&mut component, &mut mapper);
346                    entity.insert_with_relationship_hook_mode(component, relationship_hook_mode);
347                }
348            },
349            remove: |entity| {
350                entity.remove::<C>();
351            },
352            contains: |entity| entity.contains::<C>(),
353            copy: |source_world, destination_world, source_entity, destination_entity, registry| {
354                let source_component = source_world.get::<C>(source_entity).unwrap();
355                let destination_component =
356                    from_reflect_with_fallback::<C>(source_component, destination_world, registry);
357                destination_world
358                    .entity_mut(destination_entity)
359                    .insert(destination_component);
360            },
361            reflect: |entity| entity.get::<C>().map(|c| c as &dyn Reflect),
362            reflect_mut: |entity| {
363                if !C::Mutability::MUTABLE {
364                    let name = DebugName::type_name::<C>();
365                    let name = name.shortname();
366                    panic!("Cannot call `ReflectComponent::reflect_mut` on component {name}. It is immutable, and cannot modified through reflection");
367                }
368
369                // SAFETY: guard ensures `C` is a mutable component
370                unsafe {
371                    entity
372                        .into_mut_assume_mutable::<C>()
373                        .map(|c| c.map_unchanged(|value| value as &mut dyn Reflect))
374                }
375            },
376            reflect_unchecked_mut: |entity| {
377                if !C::Mutability::MUTABLE {
378                    let name = DebugName::type_name::<C>();
379                    let name = name.shortname();
380                    panic!("Cannot call `ReflectComponent::reflect_unchecked_mut` on component {name}. It is immutable, and cannot modified through reflection");
381                }
382
383                // SAFETY: reflect_unchecked_mut is an unsafe function pointer used by
384                // `reflect_unchecked_mut` which must be called with an UnsafeEntityCell with access to the component `C` on the `entity`
385                // guard ensures `C` is a mutable component
386                let c = unsafe { entity.get_mut_assume_mutable::<C>() };
387                c.map(|c| c.map_unchanged(|value| value as &mut dyn Reflect))
388            },
389            register_component: |world: &mut World| -> ComponentId {
390                world.register_component::<C>()
391            },
392            map_entities: |reflect: &mut dyn Reflect, mut mapper: &mut dyn EntityMapper| {
393                let component = reflect.downcast_mut::<C>().unwrap();
394                Component::map_entities(component, &mut mapper);
395            },
396        })
397    }
398}
bevy_ecs/reflect/component.rs

bevy_ecs/reflect/
component.rs
