//! Types for declaring and storing [`Component`]s. use crate::{ archetype::ArchetypeFlags, bundle::BundleInfo, change_detection::{MaybeLocation, MAX_CHANGE_AGE}, entity::{ComponentCloneCtx, Entity, SourceComponent}, query::DebugCheckedUnwrap, relationship::RelationshipInsertHookMode, resource::Resource, storage::{SparseSetIndex, SparseSets, Table, TableRow}, system::{Commands, Local, SystemParam}, world::{DeferredWorld, FromWorld, World}, }; #[cfg(feature = "bevy_reflect")] use alloc::boxed::Box; use alloc::{borrow::Cow, format, vec::Vec}; pub use bevy_ecs_macros::Component; use bevy_platform_support::collections::{HashMap, HashSet}; use bevy_platform_support::sync::Arc; use bevy_ptr::{OwningPtr, UnsafeCellDeref}; #[cfg(feature = "bevy_reflect")] use bevy_reflect::Reflect; use bevy_utils::TypeIdMap; use core::{ alloc::Layout, any::{Any, TypeId}, cell::UnsafeCell, fmt::Debug, marker::PhantomData, mem::needs_drop, }; use disqualified::ShortName; use thiserror::Error; /// A data type that can be used to store data for an [entity]. /// /// `Component` is a [derivable trait]: this means that a data type can implement it by applying a `#[derive(Component)]` attribute to it. /// However, components must always satisfy the `Send + Sync + 'static` trait bounds. /// /// [entity]: crate::entity /// [derivable trait]: https://doc.rust-lang.org/book/appendix-03-derivable-traits.html /// /// # Examples /// /// Components can take many forms: they are usually structs, but can also be of every other kind of data type, like enums or zero sized types. /// The following examples show how components are laid out in code. /// /// ``` /// # use bevy_ecs::component::Component; /// # struct Color; /// # /// // A component can contain data... /// #[derive(Component)] /// struct LicensePlate(String); /// /// // ... but it can also be a zero-sized marker. /// #[derive(Component)] /// struct Car; /// /// // Components can also be structs with named fields... /// #[derive(Component)] /// struct VehiclePerformance { /// acceleration: f32, /// top_speed: f32, /// handling: f32, /// } /// /// // ... or enums. /// #[derive(Component)] /// enum WheelCount { /// Two, /// Three, /// Four, /// } /// ``` /// /// # Component and data access /// /// Components can be marked as immutable by adding the `#[component(immutable)]` /// attribute when using the derive macro. /// See the documentation for [`ComponentMutability`] for more details around this /// feature. /// /// See the [`entity`] module level documentation to learn how to add or remove components from an entity. /// /// See the documentation for [`Query`] to learn how to access component data from a system. /// /// [`entity`]: crate::entity#usage /// [`Query`]: crate::system::Query /// [`ComponentMutability`]: crate::component::ComponentMutability /// /// # Choosing a storage type /// /// Components can be stored in the world using different strategies with their own performance implications. /// By default, components are added to the [`Table`] storage, which is optimized for query iteration. /// /// Alternatively, components can be added to the [`SparseSet`] storage, which is optimized for component insertion and removal. /// This is achieved by adding an additional `#[component(storage = "SparseSet")]` attribute to the derive one: /// /// ``` /// # use bevy_ecs::component::Component; /// # /// #[derive(Component)] /// #[component(storage = "SparseSet")] /// struct ComponentA; /// ``` /// /// [`Table`]: crate::storage::Table /// [`SparseSet`]: crate::storage::SparseSet /// /// # Required Components /// /// Components can specify Required Components. If some [`Component`] `A` requires [`Component`] `B`, then when `A` is inserted, /// `B` will _also_ be initialized and inserted (if it was not manually specified). /// /// The [`Default`] constructor will be used to initialize the component, by default: /// /// ``` /// # use bevy_ecs::prelude::*; /// #[derive(Component)] /// #[require(B)] /// struct A; /// /// #[derive(Component, Default, PartialEq, Eq, Debug)] /// struct B(usize); /// /// # let mut world = World::default(); /// // This will implicitly also insert B with the Default constructor /// let id = world.spawn(A).id(); /// assert_eq!(&B(0), world.entity(id).get::().unwrap()); /// /// // This will _not_ implicitly insert B, because it was already provided /// world.spawn((A, B(11))); /// ``` /// /// Components can have more than one required component: /// /// ``` /// # use bevy_ecs::prelude::*; /// #[derive(Component)] /// #[require(B, C)] /// struct A; /// /// #[derive(Component, Default, PartialEq, Eq, Debug)] /// #[require(C)] /// struct B(usize); /// /// #[derive(Component, Default, PartialEq, Eq, Debug)] /// struct C(u32); /// /// # let mut world = World::default(); /// // This will implicitly also insert B and C with their Default constructors /// let id = world.spawn(A).id(); /// assert_eq!(&B(0), world.entity(id).get::().unwrap()); /// assert_eq!(&C(0), world.entity(id).get::().unwrap()); /// ``` /// /// You can also define a custom constructor function or closure: /// /// ``` /// # use bevy_ecs::prelude::*; /// #[derive(Component)] /// #[require(C(init_c))] /// struct A; /// /// #[derive(Component, PartialEq, Eq, Debug)] /// #[require(C(|| C(20)))] /// struct B; /// /// #[derive(Component, PartialEq, Eq, Debug)] /// struct C(usize); /// /// fn init_c() -> C { /// C(10) /// } /// /// # let mut world = World::default(); /// // This will implicitly also insert C with the `|| C(20)` constructor closure /// let id = world.spawn(B).id(); /// assert_eq!(&C(20), world.entity(id).get::().unwrap()); /// ``` /// /// Required components are _recursive_. This means, if a Required Component has required components, /// those components will _also_ be inserted if they are missing: /// /// ``` /// # use bevy_ecs::prelude::*; /// #[derive(Component)] /// #[require(B)] /// struct A; /// /// #[derive(Component, Default, PartialEq, Eq, Debug)] /// #[require(C)] /// struct B(usize); /// /// #[derive(Component, Default, PartialEq, Eq, Debug)] /// struct C(u32); /// /// # let mut world = World::default(); /// // This will implicitly also insert B and C with their Default constructors /// let id = world.spawn(A).id(); /// assert_eq!(&B(0), world.entity(id).get::().unwrap()); /// assert_eq!(&C(0), world.entity(id).get::().unwrap()); /// ``` /// /// Note that cycles in the "component require tree" will result in stack overflows when attempting to /// insert a component. /// /// This "multiple inheritance" pattern does mean that it is possible to have duplicate requires for a given type /// at different levels of the inheritance tree: /// /// ``` /// # use bevy_ecs::prelude::*; /// #[derive(Component)] /// struct X(usize); /// /// #[derive(Component, Default)] /// #[require(X(|| X(1)))] /// struct Y; /// /// #[derive(Component)] /// #[require( /// Y, /// X(|| X(2)), /// )] /// struct Z; /// /// # let mut world = World::default(); /// // In this case, the x2 constructor is used for X /// let id = world.spawn(Z).id(); /// assert_eq!(2, world.entity(id).get::().unwrap().0); /// ``` /// /// In general, this shouldn't happen often, but when it does the algorithm for choosing the constructor from the tree is simple and predictable: /// 1. A constructor from a direct `#[require()]`, if one exists, is selected with priority. /// 2. Otherwise, perform a Depth First Search on the tree of requirements and select the first one found. /// /// From a user perspective, just think about this as the following: /// 1. Specifying a required component constructor for Foo directly on a spawned component Bar will result in that constructor being used (and overriding existing constructors lower in the inheritance tree). This is the classic "inheritance override" behavior people expect. /// 2. For cases where "multiple inheritance" results in constructor clashes, Components should be listed in "importance order". List a component earlier in the requirement list to initialize its inheritance tree earlier. /// /// ## Registering required components at runtime /// /// In most cases, required components should be registered using the `require` attribute as shown above. /// However, in some cases, it may be useful to register required components at runtime. /// /// This can be done through [`World::register_required_components`] or [`World::register_required_components_with`] /// for the [`Default`] and custom constructors respectively: /// /// ``` /// # use bevy_ecs::prelude::*; /// #[derive(Component)] /// struct A; /// /// #[derive(Component, Default, PartialEq, Eq, Debug)] /// struct B(usize); /// /// #[derive(Component, PartialEq, Eq, Debug)] /// struct C(u32); /// /// # let mut world = World::default(); /// // Register B as required by A and C as required by B. /// world.register_required_components::(); /// world.register_required_components_with::(|| C(2)); /// /// // This will implicitly also insert B with its Default constructor /// // and C with the custom constructor defined by B. /// let id = world.spawn(A).id(); /// assert_eq!(&B(0), world.entity(id).get::().unwrap()); /// assert_eq!(&C(2), world.entity(id).get::().unwrap()); /// ``` /// /// Similar rules as before apply to duplicate requires fer a given type at different levels /// of the inheritance tree. `A` requiring `C` directly would take precedence over indirectly /// requiring it through `A` requiring `B` and `B` requiring `C`. /// /// Unlike with the `require` attribute, directly requiring the same component multiple times /// for the same component will result in a panic. This is done to prevent conflicting constructors /// and confusing ordering dependencies. /// /// Note that requirements must currently be registered before the requiring component is inserted /// into the world for the first time. Registering requirements after this will lead to a panic. /// /// # Adding component's hooks /// /// See [`ComponentHooks`] for a detailed explanation of component's hooks. /// /// Alternatively to the example shown in [`ComponentHooks`]' documentation, hooks can be configured using following attributes: /// - `#[component(on_add = on_add_function)]` /// - `#[component(on_insert = on_insert_function)]` /// - `#[component(on_replace = on_replace_function)]` /// - `#[component(on_remove = on_remove_function)]` /// /// ``` /// # use bevy_ecs::component::{Component, HookContext}; /// # use bevy_ecs::world::DeferredWorld; /// # use bevy_ecs::entity::Entity; /// # use bevy_ecs::component::ComponentId; /// # use core::panic::Location; /// # /// #[derive(Component)] /// #[component(on_add = my_on_add_hook)] /// #[component(on_insert = my_on_insert_hook)] /// // Another possible way of configuring hooks: /// // #[component(on_add = my_on_add_hook, on_insert = my_on_insert_hook)] /// // /// // We don't have a replace or remove hook, so we can leave them out: /// // #[component(on_replace = my_on_replace_hook, on_remove = my_on_remove_hook)] /// struct ComponentA; /// /// fn my_on_add_hook(world: DeferredWorld, context: HookContext) { /// // ... /// } /// /// // You can also destructure items directly in the signature /// fn my_on_insert_hook(world: DeferredWorld, HookContext { caller, .. }: HookContext) { /// // ... /// } /// ``` /// /// This also supports function calls that yield closures /// /// ``` /// # use bevy_ecs::component::{Component, HookContext}; /// # use bevy_ecs::world::DeferredWorld; /// # /// #[derive(Component)] /// #[component(on_add = my_msg_hook("hello"))] /// #[component(on_despawn = my_msg_hook("yoink"))] /// struct ComponentA; /// /// // a hook closure generating function /// fn my_msg_hook(message: &'static str) -> impl Fn(DeferredWorld, HookContext) { /// move |_world, _ctx| { /// println!("{message}"); /// } /// } /// ``` /// /// # Implementing the trait for foreign types /// /// As a consequence of the [orphan rule], it is not possible to separate into two different crates the implementation of `Component` from the definition of a type. /// This means that it is not possible to directly have a type defined in a third party library as a component. /// This important limitation can be easily worked around using the [newtype pattern]: /// this makes it possible to locally define and implement `Component` for a tuple struct that wraps the foreign type. /// The following example gives a demonstration of this pattern. /// /// ``` /// // `Component` is defined in the `bevy_ecs` crate. /// use bevy_ecs::component::Component; /// /// // `Duration` is defined in the `std` crate. /// use std::time::Duration; /// /// // It is not possible to implement `Component` for `Duration` from this position, as they are /// // both foreign items, defined in an external crate. However, nothing prevents to define a new /// // `Cooldown` type that wraps `Duration`. As `Cooldown` is defined in a local crate, it is /// // possible to implement `Component` for it. /// #[derive(Component)] /// struct Cooldown(Duration); /// ``` /// /// [orphan rule]: https://doc.rust-lang.org/book/ch10-02-traits.html#implementing-a-trait-on-a-type /// [newtype pattern]: https://doc.rust-lang.org/book/ch19-03-advanced-traits.html#using-the-newtype-pattern-to-implement-external-traits-on-external-types /// /// # `!Sync` Components /// A `!Sync` type cannot implement `Component`. However, it is possible to wrap a `Send` but not `Sync` /// type in [`SyncCell`] or the currently unstable [`Exclusive`] to make it `Sync`. This forces only /// having mutable access (`&mut T` only, never `&T`), but makes it safe to reference across multiple /// threads. /// /// This will fail to compile since `RefCell` is `!Sync`. /// ```compile_fail /// # use std::cell::RefCell; /// # use bevy_ecs::component::Component; /// #[derive(Component)] /// struct NotSync { /// counter: RefCell, /// } /// ``` /// /// This will compile since the `RefCell` is wrapped with `SyncCell`. /// ``` /// # use std::cell::RefCell; /// # use bevy_ecs::component::Component; /// use bevy_utils::synccell::SyncCell; /// /// // This will compile. /// #[derive(Component)] /// struct ActuallySync { /// counter: SyncCell>, /// } /// ``` /// /// [`SyncCell`]: bevy_utils::synccell::SyncCell /// [`Exclusive`]: https://doc.rust-lang.org/nightly/std/sync/struct.Exclusive.html #[diagnostic::on_unimplemented( message = "`{Self}` is not a `Component`", label = "invalid `Component`", note = "consider annotating `{Self}` with `#[derive(Component)]`" )] pub trait Component: Send + Sync + 'static { /// A constant indicating the storage type used for this component. const STORAGE_TYPE: StorageType; /// A marker type to assist Bevy with determining if this component is /// mutable, or immutable. Mutable components will have [`Component`], /// while immutable components will instead have [`Component`]. /// /// * For a component to be mutable, this type must be [`Mutable`]. /// * For a component to be immutable, this type must be [`Immutable`]. type Mutability: ComponentMutability; /// Called when registering this component, allowing mutable access to its [`ComponentHooks`]. #[deprecated( since = "0.16.0", note = "Use the individual hook methods instead (e.g., `Component::on_add`, etc.)" )] fn register_component_hooks(hooks: &mut ComponentHooks) { hooks.update_from_component::(); } /// Gets the `on_add` [`ComponentHook`] for this [`Component`] if one is defined. fn on_add() -> Option { None } /// Gets the `on_insert` [`ComponentHook`] for this [`Component`] if one is defined. fn on_insert() -> Option { None } /// Gets the `on_replace` [`ComponentHook`] for this [`Component`] if one is defined. fn on_replace() -> Option { None } /// Gets the `on_remove` [`ComponentHook`] for this [`Component`] if one is defined. fn on_remove() -> Option { None } /// Gets the `on_despawn` [`ComponentHook`] for this [`Component`] if one is defined. fn on_despawn() -> Option { None } /// Registers required components. fn register_required_components( _component_id: ComponentId, _components: &mut Components, _required_components: &mut RequiredComponents, _inheritance_depth: u16, _recursion_check_stack: &mut Vec, ) { } /// Called when registering this component, allowing to override clone function (or disable cloning altogether) for this component. /// /// See [Handlers section of `EntityClonerBuilder`](crate::entity::EntityClonerBuilder#handlers) to understand how this affects handler priority. #[inline] fn clone_behavior() -> ComponentCloneBehavior { ComponentCloneBehavior::Default } /// Visits entities stored on the component. #[inline] fn visit_entities(_this: &Self, _f: impl FnMut(Entity)) {} /// Returns pointers to every entity stored on the component. This will be used to remap entity references when this entity /// is cloned. #[inline] fn visit_entities_mut(_this: &mut Self, _f: impl FnMut(&mut Entity)) {} } mod private { pub trait Seal {} } /// The mutability option for a [`Component`]. This can either be: /// * [`Mutable`] /// * [`Immutable`] /// /// This is controlled through either [`Component::Mutability`] or `#[component(immutable)]` /// when using the derive macro. /// /// Immutable components are guaranteed to never have an exclusive reference, /// `&mut ...`, created while inserted onto an entity. /// In all other ways, they are identical to mutable components. /// This restriction allows hooks to observe all changes made to an immutable /// component, effectively turning the `OnInsert` and `OnReplace` hooks into a /// `OnMutate` hook. /// This is not practical for mutable components, as the runtime cost of invoking /// a hook for every exclusive reference created would be far too high. /// /// # Examples /// /// ```rust /// # use bevy_ecs::component::Component; /// # /// #[derive(Component)] /// #[component(immutable)] /// struct ImmutableFoo; /// ``` pub trait ComponentMutability: private::Seal + 'static { /// Boolean to indicate if this mutability setting implies a mutable or immutable /// component. const MUTABLE: bool; } /// Parameter indicating a [`Component`] is immutable. /// /// See [`ComponentMutability`] for details. pub struct Immutable; impl private::Seal for Immutable {} impl ComponentMutability for Immutable { const MUTABLE: bool = false; } /// Parameter indicating a [`Component`] is mutable. /// /// See [`ComponentMutability`] for details. pub struct Mutable; impl private::Seal for Mutable {} impl ComponentMutability for Mutable { const MUTABLE: bool = true; } /// The storage used for a specific component type. /// /// # Examples /// The [`StorageType`] for a component is configured via the derive attribute /// /// ``` /// # use bevy_ecs::{prelude::*, component::*}; /// #[derive(Component)] /// #[component(storage = "SparseSet")] /// struct A; /// ``` #[derive(Debug, Copy, Clone, Default, Eq, PartialEq)] pub enum StorageType { /// Provides fast and cache-friendly iteration, but slower addition and removal of components. /// This is the default storage type. #[default] Table, /// Provides fast addition and removal of components, but slower iteration. SparseSet, } /// The type used for [`Component`] lifecycle hooks such as `on_add`, `on_insert` or `on_remove`. pub type ComponentHook = for<'w> fn(DeferredWorld<'w>, HookContext); /// Context provided to a [`ComponentHook`]. #[derive(Clone, Copy, Debug)] pub struct HookContext { /// The [`Entity`] this hook was invoked for. pub entity: Entity, /// The [`ComponentId`] this hook was invoked for. pub component_id: ComponentId, /// The caller location is `Some` if the `track_caller` feature is enabled. pub caller: MaybeLocation, /// Configures how relationship hooks will run pub relationship_insert_hook_mode: RelationshipInsertHookMode, } /// [`World`]-mutating functions that run as part of lifecycle events of a [`Component`]. /// /// Hooks are functions that run when a component is added, overwritten, or removed from an entity. /// These are intended to be used for structural side effects that need to happen when a component is added or removed, /// and are not intended for general-purpose logic. /// /// For example, you might use a hook to update a cached index when a component is added, /// to clean up resources when a component is removed, /// or to keep hierarchical data structures across entities in sync. /// /// This information is stored in the [`ComponentInfo`] of the associated component. /// /// There is two ways of configuring hooks for a component: /// 1. Defining the [`Component::register_component_hooks`] method (see [`Component`]) /// 2. Using the [`World::register_component_hooks`] method /// /// # Example 2 /// /// ``` /// use bevy_ecs::prelude::*; /// use bevy_platform_support::collections::HashSet; /// /// #[derive(Component)] /// struct MyTrackedComponent; /// /// #[derive(Resource, Default)] /// struct TrackedEntities(HashSet); /// /// let mut world = World::new(); /// world.init_resource::(); /// /// // No entities with `MyTrackedComponent` have been added yet, so we can safely add component hooks /// let mut tracked_component_query = world.query::<&MyTrackedComponent>(); /// assert!(tracked_component_query.iter(&world).next().is_none()); /// /// world.register_component_hooks::().on_add(|mut world, context| { /// let mut tracked_entities = world.resource_mut::(); /// tracked_entities.0.insert(context.entity); /// }); /// /// world.register_component_hooks::().on_remove(|mut world, context| { /// let mut tracked_entities = world.resource_mut::(); /// tracked_entities.0.remove(&context.entity); /// }); /// /// let entity = world.spawn(MyTrackedComponent).id(); /// let tracked_entities = world.resource::(); /// assert!(tracked_entities.0.contains(&entity)); /// /// world.despawn(entity); /// let tracked_entities = world.resource::(); /// assert!(!tracked_entities.0.contains(&entity)); /// ``` #[derive(Debug, Clone, Default)] pub struct ComponentHooks { pub(crate) on_add: Option, pub(crate) on_insert: Option, pub(crate) on_replace: Option, pub(crate) on_remove: Option, pub(crate) on_despawn: Option, } impl ComponentHooks { pub(crate) fn update_from_component(&mut self) -> &mut Self { if let Some(hook) = C::on_add() { self.on_add(hook); } if let Some(hook) = C::on_insert() { self.on_insert(hook); } if let Some(hook) = C::on_replace() { self.on_replace(hook); } if let Some(hook) = C::on_remove() { self.on_remove(hook); } if let Some(hook) = C::on_despawn() { self.on_despawn(hook); } self } /// Register a [`ComponentHook`] that will be run when this component is added to an entity. /// An `on_add` hook will always run before `on_insert` hooks. Spawning an entity counts as /// adding all of its components. /// /// # Panics /// /// Will panic if the component already has an `on_add` hook pub fn on_add(&mut self, hook: ComponentHook) -> &mut Self { self.try_on_add(hook) .expect("Component already has an on_add hook") } /// Register a [`ComponentHook`] that will be run when this component is added (with `.insert`) /// or replaced. /// /// An `on_insert` hook always runs after any `on_add` hooks (if the entity didn't already have the component). /// /// # Warning /// /// The hook won't run if the component is already present and is only mutated, such as in a system via a query. /// As a result, this is *not* an appropriate mechanism for reliably updating indexes and other caches. /// /// # Panics /// /// Will panic if the component already has an `on_insert` hook pub fn on_insert(&mut self, hook: ComponentHook) -> &mut Self { self.try_on_insert(hook) .expect("Component already has an on_insert hook") } /// Register a [`ComponentHook`] that will be run when this component is about to be dropped, /// such as being replaced (with `.insert`) or removed. /// /// If this component is inserted onto an entity that already has it, this hook will run before the value is replaced, /// allowing access to the previous data just before it is dropped. /// This hook does *not* run if the entity did not already have this component. /// /// An `on_replace` hook always runs before any `on_remove` hooks (if the component is being removed from the entity). /// /// # Warning /// /// The hook won't run if the component is already present and is only mutated, such as in a system via a query. /// As a result, this is *not* an appropriate mechanism for reliably updating indexes and other caches. /// /// # Panics /// /// Will panic if the component already has an `on_replace` hook pub fn on_replace(&mut self, hook: ComponentHook) -> &mut Self { self.try_on_replace(hook) .expect("Component already has an on_replace hook") } /// Register a [`ComponentHook`] that will be run when this component is removed from an entity. /// Despawning an entity counts as removing all of its components. /// /// # Panics /// /// Will panic if the component already has an `on_remove` hook pub fn on_remove(&mut self, hook: ComponentHook) -> &mut Self { self.try_on_remove(hook) .expect("Component already has an on_remove hook") } /// Register a [`ComponentHook`] that will be run for each component on an entity when it is despawned. /// /// # Panics /// /// Will panic if the component already has an `on_despawn` hook pub fn on_despawn(&mut self, hook: ComponentHook) -> &mut Self { self.try_on_despawn(hook) .expect("Component already has an on_despawn hook") } /// Attempt to register a [`ComponentHook`] that will be run when this component is added to an entity. /// /// This is a fallible version of [`Self::on_add`]. /// /// Returns `None` if the component already has an `on_add` hook. pub fn try_on_add(&mut self, hook: ComponentHook) -> Option<&mut Self> { if self.on_add.is_some() { return None; } self.on_add = Some(hook); Some(self) } /// Attempt to register a [`ComponentHook`] that will be run when this component is added (with `.insert`) /// /// This is a fallible version of [`Self::on_insert`]. /// /// Returns `None` if the component already has an `on_insert` hook. pub fn try_on_insert(&mut self, hook: ComponentHook) -> Option<&mut Self> { if self.on_insert.is_some() { return None; } self.on_insert = Some(hook); Some(self) } /// Attempt to register a [`ComponentHook`] that will be run when this component is replaced (with `.insert`) or removed /// /// This is a fallible version of [`Self::on_replace`]. /// /// Returns `None` if the component already has an `on_replace` hook. pub fn try_on_replace(&mut self, hook: ComponentHook) -> Option<&mut Self> { if self.on_replace.is_some() { return None; } self.on_replace = Some(hook); Some(self) } /// Attempt to register a [`ComponentHook`] that will be run when this component is removed from an entity. /// /// This is a fallible version of [`Self::on_remove`]. /// /// Returns `None` if the component already has an `on_remove` hook. pub fn try_on_remove(&mut self, hook: ComponentHook) -> Option<&mut Self> { if self.on_remove.is_some() { return None; } self.on_remove = Some(hook); Some(self) } /// Attempt to register a [`ComponentHook`] that will be run for each component on an entity when it is despawned. /// /// This is a fallible version of [`Self::on_despawn`]. /// /// Returns `None` if the component already has an `on_despawn` hook. pub fn try_on_despawn(&mut self, hook: ComponentHook) -> Option<&mut Self> { if self.on_despawn.is_some() { return None; } self.on_despawn = Some(hook); Some(self) } } /// Stores metadata for a type of component or resource stored in a specific [`World`]. #[derive(Debug, Clone)] pub struct ComponentInfo { id: ComponentId, descriptor: ComponentDescriptor, hooks: ComponentHooks, required_components: RequiredComponents, required_by: HashSet, } impl ComponentInfo { /// Returns a value uniquely identifying the current component. #[inline] pub fn id(&self) -> ComponentId { self.id } /// Returns the name of the current component. #[inline] pub fn name(&self) -> &str { &self.descriptor.name } /// Returns `true` if the current component is mutable. #[inline] pub fn mutable(&self) -> bool { self.descriptor.mutable } /// Returns [`ComponentCloneBehavior`] of the current component. #[inline] pub fn clone_behavior(&self) -> &ComponentCloneBehavior { &self.descriptor.clone_behavior } /// Returns the [`TypeId`] of the underlying component type. /// Returns `None` if the component does not correspond to a Rust type. #[inline] pub fn type_id(&self) -> Option { self.descriptor.type_id } /// Returns the layout used to store values of this component in memory. #[inline] pub fn layout(&self) -> Layout { self.descriptor.layout } #[inline] /// Get the function which should be called to clean up values of /// the underlying component type. This maps to the /// [`Drop`] implementation for 'normal' Rust components /// /// Returns `None` if values of the underlying component type don't /// need to be dropped, e.g. as reported by [`needs_drop`]. pub fn drop(&self) -> Option)> { self.descriptor.drop } /// Returns a value indicating the storage strategy for the current component. #[inline] pub fn storage_type(&self) -> StorageType { self.descriptor.storage_type } /// Returns `true` if the underlying component type can be freely shared between threads. /// If this returns `false`, then extra care must be taken to ensure that components /// are not accessed from the wrong thread. #[inline] pub fn is_send_and_sync(&self) -> bool { self.descriptor.is_send_and_sync } /// Create a new [`ComponentInfo`]. pub(crate) fn new(id: ComponentId, descriptor: ComponentDescriptor) -> Self { ComponentInfo { id, descriptor, hooks: Default::default(), required_components: Default::default(), required_by: Default::default(), } } /// Update the given flags to include any [`ComponentHook`] registered to self #[inline] pub(crate) fn update_archetype_flags(&self, flags: &mut ArchetypeFlags) { if self.hooks().on_add.is_some() { flags.insert(ArchetypeFlags::ON_ADD_HOOK); } if self.hooks().on_insert.is_some() { flags.insert(ArchetypeFlags::ON_INSERT_HOOK); } if self.hooks().on_replace.is_some() { flags.insert(ArchetypeFlags::ON_REPLACE_HOOK); } if self.hooks().on_remove.is_some() { flags.insert(ArchetypeFlags::ON_REMOVE_HOOK); } if self.hooks().on_despawn.is_some() { flags.insert(ArchetypeFlags::ON_DESPAWN_HOOK); } } /// Provides a reference to the collection of hooks associated with this [`Component`] pub fn hooks(&self) -> &ComponentHooks { &self.hooks } /// Retrieves the [`RequiredComponents`] collection, which contains all required components (and their constructors) /// needed by this component. This includes _recursive_ required components. pub fn required_components(&self) -> &RequiredComponents { &self.required_components } } /// A value which uniquely identifies the type of a [`Component`] or [`Resource`] within a /// [`World`]. /// /// Each time a new `Component` type is registered within a `World` using /// e.g. [`World::register_component`] or [`World::register_component_with_descriptor`] /// or a Resource with e.g. [`World::init_resource`], /// a corresponding `ComponentId` is created to track it. /// /// While the distinction between `ComponentId` and [`TypeId`] may seem superficial, breaking them /// into two separate but related concepts allows components to exist outside of Rust's type system. /// Each Rust type registered as a `Component` will have a corresponding `ComponentId`, but additional /// `ComponentId`s may exist in a `World` to track components which cannot be /// represented as Rust types for scripting or other advanced use-cases. /// /// A `ComponentId` is tightly coupled to its parent `World`. Attempting to use a `ComponentId` from /// one `World` to access the metadata of a `Component` in a different `World` is undefined behavior /// and must not be attempted. /// /// Given a type `T` which implements [`Component`], the `ComponentId` for `T` can be retrieved /// from a `World` using [`World::component_id()`] or via [`Components::component_id()`]. Access /// to the `ComponentId` for a [`Resource`] is available via [`Components::resource_id()`]. #[derive(Debug, Copy, Clone, Hash, Ord, PartialOrd, Eq, PartialEq)] #[cfg_attr( feature = "bevy_reflect", derive(Reflect), reflect(Debug, Hash, PartialEq) )] pub struct ComponentId(usize); impl ComponentId { /// Creates a new [`ComponentId`]. /// /// The `index` is a unique value associated with each type of component in a given world. /// Usually, this value is taken from a counter incremented for each type of component registered with the world. #[inline] pub const fn new(index: usize) -> ComponentId { ComponentId(index) } /// Returns the index of the current component. #[inline] pub fn index(self) -> usize { self.0 } } impl SparseSetIndex for ComponentId { #[inline] fn sparse_set_index(&self) -> usize { self.index() } #[inline] fn get_sparse_set_index(value: usize) -> Self { Self(value) } } /// A value describing a component or resource, which may or may not correspond to a Rust type. #[derive(Clone)] pub struct ComponentDescriptor { name: Cow<'static, str>, // SAFETY: This must remain private. It must match the statically known StorageType of the // associated rust component type if one exists. storage_type: StorageType, // SAFETY: This must remain private. It must only be set to "true" if this component is // actually Send + Sync is_send_and_sync: bool, type_id: Option, layout: Layout, // SAFETY: this function must be safe to call with pointers pointing to items of the type // this descriptor describes. // None if the underlying type doesn't need to be dropped drop: Option unsafe fn(OwningPtr<'a>)>, mutable: bool, clone_behavior: ComponentCloneBehavior, } // We need to ignore the `drop` field in our `Debug` impl impl Debug for ComponentDescriptor { fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { f.debug_struct("ComponentDescriptor") .field("name", &self.name) .field("storage_type", &self.storage_type) .field("is_send_and_sync", &self.is_send_and_sync) .field("type_id", &self.type_id) .field("layout", &self.layout) .field("mutable", &self.mutable) .field("clone_behavior", &self.clone_behavior) .finish() } } impl ComponentDescriptor { /// # Safety /// /// `x` must point to a valid value of type `T`. unsafe fn drop_ptr(x: OwningPtr<'_>) { // SAFETY: Contract is required to be upheld by the caller. unsafe { x.drop_as::(); } } /// Create a new `ComponentDescriptor` for the type `T`. pub fn new() -> Self { Self { name: Cow::Borrowed(core::any::type_name::()), storage_type: T::STORAGE_TYPE, is_send_and_sync: true, type_id: Some(TypeId::of::()), layout: Layout::new::(), drop: needs_drop::().then_some(Self::drop_ptr:: as _), mutable: T::Mutability::MUTABLE, clone_behavior: T::clone_behavior(), } } /// Create a new `ComponentDescriptor`. /// /// # Safety /// - the `drop` fn must be usable on a pointer with a value of the layout `layout` /// - the component type must be safe to access from any thread (Send + Sync in rust terms) pub unsafe fn new_with_layout( name: impl Into>, storage_type: StorageType, layout: Layout, drop: Option unsafe fn(OwningPtr<'a>)>, mutable: bool, clone_behavior: ComponentCloneBehavior, ) -> Self { Self { name: name.into(), storage_type, is_send_and_sync: true, type_id: None, layout, drop, mutable, clone_behavior, } } /// Create a new `ComponentDescriptor` for a resource. /// /// The [`StorageType`] for resources is always [`StorageType::Table`]. pub fn new_resource() -> Self { Self { name: Cow::Borrowed(core::any::type_name::()), // PERF: `SparseStorage` may actually be a more // reasonable choice as `storage_type` for resources. storage_type: StorageType::Table, is_send_and_sync: true, type_id: Some(TypeId::of::()), layout: Layout::new::(), drop: needs_drop::().then_some(Self::drop_ptr:: as _), mutable: true, clone_behavior: ComponentCloneBehavior::Default, } } fn new_non_send(storage_type: StorageType) -> Self { Self { name: Cow::Borrowed(core::any::type_name::()), storage_type, is_send_and_sync: false, type_id: Some(TypeId::of::()), layout: Layout::new::(), drop: needs_drop::().then_some(Self::drop_ptr:: as _), mutable: true, clone_behavior: ComponentCloneBehavior::Default, } } /// Returns a value indicating the storage strategy for the current component. #[inline] pub fn storage_type(&self) -> StorageType { self.storage_type } /// Returns the [`TypeId`] of the underlying component type. /// Returns `None` if the component does not correspond to a Rust type. #[inline] pub fn type_id(&self) -> Option { self.type_id } /// Returns the name of the current component. #[inline] pub fn name(&self) -> &str { self.name.as_ref() } /// Returns whether this component is mutable. #[inline] pub fn mutable(&self) -> bool { self.mutable } } /// Function type that can be used to clone an entity. pub type ComponentCloneFn = fn(&mut Commands, &SourceComponent, &mut ComponentCloneCtx); /// The clone behavior to use when cloning a [`Component`]. #[derive(Clone, Debug, Default, PartialEq, Eq)] pub enum ComponentCloneBehavior { /// Uses the default behavior (which is passed to [`ComponentCloneBehavior::resolve`]) #[default] Default, /// Do not clone this component. Ignore, /// Uses a custom [`ComponentCloneFn`]. Custom(ComponentCloneFn), } impl ComponentCloneBehavior { /// Set clone handler based on `Clone` trait. /// /// If set as a handler for a component that is not the same as the one used to create this handler, it will panic. pub fn clone() -> Self { Self::Custom(component_clone_via_clone::) } /// Set clone handler based on `Reflect` trait. #[cfg(feature = "bevy_reflect")] pub fn reflect() -> Self { Self::Custom(component_clone_via_reflect) } /// Returns the "global default" pub fn global_default_fn() -> ComponentCloneFn { #[cfg(feature = "bevy_reflect")] return component_clone_via_reflect; #[cfg(not(feature = "bevy_reflect"))] return component_clone_ignore; } /// Resolves the [`ComponentCloneBehavior`] to a [`ComponentCloneFn`]. If [`ComponentCloneBehavior::Default`] is /// specified, the given `default` function will be used. pub fn resolve(&self, default: ComponentCloneFn) -> ComponentCloneFn { match self { ComponentCloneBehavior::Default => default, ComponentCloneBehavior::Ignore => component_clone_ignore, ComponentCloneBehavior::Custom(custom) => *custom, } } } /// Stores metadata associated with each kind of [`Component`] in a given [`World`]. #[derive(Debug, Default)] pub struct Components { components: Vec, indices: TypeIdMap, resource_indices: TypeIdMap, } impl Components { /// Registers a [`Component`] of type `T` with this instance. /// If a component of this type has already been registered, this will return /// the ID of the pre-existing component. /// /// # See also /// /// * [`Components::component_id()`] /// * [`Components::register_component_with_descriptor()`] #[inline] pub fn register_component(&mut self) -> ComponentId { self.register_component_internal::(&mut Vec::new()) } #[inline] fn register_component_internal( &mut self, recursion_check_stack: &mut Vec, ) -> ComponentId { let mut is_new_registration = false; let id = { let Components { indices, components, .. } = self; let type_id = TypeId::of::(); *indices.entry(type_id).or_insert_with(|| { let id = Components::register_component_inner( components, ComponentDescriptor::new::(), ); is_new_registration = true; id }) }; if is_new_registration { let mut required_components = RequiredComponents::default(); T::register_required_components( id, self, &mut required_components, 0, recursion_check_stack, ); let info = &mut self.components[id.index()]; #[expect( deprecated, reason = "need to use this method until it is removed to ensure user defined components register hooks correctly" )] // TODO: Replace with `info.hooks.update_from_component::();` once `Component::register_component_hooks` is removed T::register_component_hooks(&mut info.hooks); info.required_components = required_components; } id } /// Registers a component described by `descriptor`. /// /// # Note /// /// If this method is called multiple times with identical descriptors, a distinct [`ComponentId`] /// will be created for each one. /// /// # See also /// /// * [`Components::component_id()`] /// * [`Components::register_component()`] pub fn register_component_with_descriptor( &mut self, descriptor: ComponentDescriptor, ) -> ComponentId { Components::register_component_inner(&mut self.components, descriptor) } #[inline] fn register_component_inner( components: &mut Vec, descriptor: ComponentDescriptor, ) -> ComponentId { let component_id = ComponentId(components.len()); let info = ComponentInfo::new(component_id, descriptor); components.push(info); component_id } /// Returns the number of components registered with this instance. #[inline] pub fn len(&self) -> usize { self.components.len() } /// Returns `true` if there are no components registered with this instance. Otherwise, this returns `false`. #[inline] pub fn is_empty(&self) -> bool { self.components.len() == 0 } /// Gets the metadata associated with the given component. /// /// This will return an incorrect result if `id` did not come from the same world as `self`. It may return `None` or a garbage value. #[inline] pub fn get_info(&self, id: ComponentId) -> Option<&ComponentInfo> { self.components.get(id.0) } /// Returns the name associated with the given component. /// /// This will return an incorrect result if `id` did not come from the same world as `self`. It may return `None` or a garbage value. #[inline] pub fn get_name(&self, id: ComponentId) -> Option<&str> { self.get_info(id).map(ComponentInfo::name) } /// Gets the metadata associated with the given component. /// # Safety /// /// `id` must be a valid [`ComponentId`] #[inline] pub unsafe fn get_info_unchecked(&self, id: ComponentId) -> &ComponentInfo { debug_assert!(id.index() < self.components.len()); // SAFETY: The caller ensures `id` is valid. unsafe { self.components.get_unchecked(id.0) } } #[inline] pub(crate) fn get_hooks_mut(&mut self, id: ComponentId) -> Option<&mut ComponentHooks> { self.components.get_mut(id.0).map(|info| &mut info.hooks) } #[inline] pub(crate) fn get_required_components_mut( &mut self, id: ComponentId, ) -> Option<&mut RequiredComponents> { self.components .get_mut(id.0) .map(|info| &mut info.required_components) } /// Registers the given component `R` and [required components] inherited from it as required by `T`. /// /// When `T` is added to an entity, `R` will also be added if it was not already provided. /// The given `constructor` will be used for the creation of `R`. /// /// [required components]: Component#required-components /// /// # Safety /// /// The given component IDs `required` and `requiree` must be valid. /// /// # Errors /// /// Returns a [`RequiredComponentsError`] if the `required` component is already a directly required component for the `requiree`. /// /// Indirect requirements through other components are allowed. In those cases, the more specific /// registration will be used. pub(crate) unsafe fn register_required_components( &mut self, requiree: ComponentId, required: ComponentId, constructor: fn() -> R, ) -> Result<(), RequiredComponentsError> { // SAFETY: The caller ensures that the `requiree` is valid. let required_components = unsafe { self.get_required_components_mut(requiree) .debug_checked_unwrap() }; // Cannot directly require the same component twice. if required_components .0 .get(&required) .is_some_and(|c| c.inheritance_depth == 0) { return Err(RequiredComponentsError::DuplicateRegistration( requiree, required, )); } // Register the required component for the requiree. // This is a direct requirement with a depth of `0`. required_components.register_by_id(required, constructor, 0); // Add the requiree to the list of components that require the required component. // SAFETY: The component is in the list of required components, so it must exist already. let required_by = unsafe { self.get_required_by_mut(required).debug_checked_unwrap() }; required_by.insert(requiree); let mut required_components_tmp = RequiredComponents::default(); // SAFETY: The caller ensures that the `requiree` and `required` components are valid. let inherited_requirements = unsafe { self.register_inherited_required_components( requiree, required, &mut required_components_tmp, ) }; // SAFETY: The caller ensures that the `requiree` is valid. let required_components = unsafe { self.get_required_components_mut(requiree) .debug_checked_unwrap() }; required_components.0.extend(required_components_tmp.0); // Propagate the new required components up the chain to all components that require the requiree. if let Some(required_by) = self.get_required_by(requiree).cloned() { // `required` is now required by anything that `requiree` was required by. self.get_required_by_mut(required) .unwrap() .extend(required_by.iter().copied()); for &required_by_id in required_by.iter() { // SAFETY: The component is in the list of required components, so it must exist already. let required_components = unsafe { self.get_required_components_mut(required_by_id) .debug_checked_unwrap() }; // Register the original required component in the "parent" of the requiree. // The inheritance depth is 1 deeper than the `requiree` wrt `required_by_id`. let depth = required_components.0.get(&requiree).expect("requiree is required by required_by_id, so its required_components must include requiree").inheritance_depth; required_components.register_by_id(required, constructor, depth + 1); for (component_id, component) in inherited_requirements.iter() { // Register the required component. // The inheritance depth of inherited components is whatever the requiree's // depth is relative to `required_by_id`, plus the inheritance depth of the // inherited component relative to the requiree, plus 1 to account for the // requiree in between. // SAFETY: Component ID and constructor match the ones on the original requiree. // The original requiree is responsible for making sure the registration is safe. unsafe { required_components.register_dynamic( *component_id, component.constructor.clone(), component.inheritance_depth + depth + 1, ); }; } } } Ok(()) } /// Registers the components inherited from `required` for the given `requiree`, /// returning the requirements in a list. /// /// # Safety /// /// The given component IDs `requiree` and `required` must be valid. unsafe fn register_inherited_required_components( &mut self, requiree: ComponentId, required: ComponentId, required_components: &mut RequiredComponents, ) -> Vec<(ComponentId, RequiredComponent)> { // Get required components inherited from the `required` component. // SAFETY: The caller ensures that the `required` component is valid. let required_component_info = unsafe { self.get_info(required).debug_checked_unwrap() }; let inherited_requirements: Vec<(ComponentId, RequiredComponent)> = required_component_info .required_components() .0 .iter() .map(|(component_id, required_component)| { ( *component_id, RequiredComponent { constructor: required_component.constructor.clone(), // Add `1` to the inheritance depth since this will be registered // for the component that requires `required`. inheritance_depth: required_component.inheritance_depth + 1, }, ) }) .collect(); // Register the new required components. for (component_id, component) in inherited_requirements.iter().cloned() { // Register the required component for the requiree. // SAFETY: Component ID and constructor match the ones on the original requiree. unsafe { required_components.register_dynamic( component_id, component.constructor, component.inheritance_depth, ); }; // Add the requiree to the list of components that require the required component. // SAFETY: The caller ensures that the required components are valid. let required_by = unsafe { self.get_required_by_mut(component_id) .debug_checked_unwrap() }; required_by.insert(requiree); } inherited_requirements } // NOTE: This should maybe be private, but it is currently public so that `bevy_ecs_macros` can use it. // We can't directly move this there either, because this uses `Components::get_required_by_mut`, // which is private, and could be equally risky to expose to users. /// Registers the given component `R` and [required components] inherited from it as required by `T`, /// and adds `T` to their lists of requirees. /// /// The given `inheritance_depth` determines how many levels of inheritance deep the requirement is. /// A direct requirement has a depth of `0`, and each level of inheritance increases the depth by `1`. /// Lower depths are more specific requirements, and can override existing less specific registrations. /// /// The `recursion_check_stack` allows checking whether this component tried to register itself as its /// own (indirect) required component. /// /// This method does *not* register any components as required by components that require `T`. /// /// Only use this method if you know what you are doing. In most cases, you should instead use [`World::register_required_components`], /// or the equivalent method in `bevy_app::App`. /// /// [required component]: Component#required-components #[doc(hidden)] pub fn register_required_components_manual( &mut self, required_components: &mut RequiredComponents, constructor: fn() -> R, inheritance_depth: u16, recursion_check_stack: &mut Vec, ) { let requiree = self.register_component_internal::(recursion_check_stack); let required = self.register_component_internal::(recursion_check_stack); // SAFETY: We just created the components. unsafe { self.register_required_components_manual_unchecked::( requiree, required, required_components, constructor, inheritance_depth, ); } } /// Registers the given component `R` and [required components] inherited from it as required by `T`, /// and adds `T` to their lists of requirees. /// /// The given `inheritance_depth` determines how many levels of inheritance deep the requirement is. /// A direct requirement has a depth of `0`, and each level of inheritance increases the depth by `1`. /// Lower depths are more specific requirements, and can override existing less specific registrations. /// /// This method does *not* register any components as required by components that require `T`. /// /// [required component]: Component#required-components /// /// # Safety /// /// The given component IDs `required` and `requiree` must be valid. pub(crate) unsafe fn register_required_components_manual_unchecked( &mut self, requiree: ComponentId, required: ComponentId, required_components: &mut RequiredComponents, constructor: fn() -> R, inheritance_depth: u16, ) { // Components cannot require themselves. if required == requiree { return; } // Register the required component `R` for the requiree. required_components.register_by_id(required, constructor, inheritance_depth); // Add the requiree to the list of components that require `R`. // SAFETY: The caller ensures that the component ID is valid. // Assuming it is valid, the component is in the list of required components, so it must exist already. let required_by = unsafe { self.get_required_by_mut(required).debug_checked_unwrap() }; required_by.insert(requiree); self.register_inherited_required_components(requiree, required, required_components); } #[inline] pub(crate) fn get_required_by(&self, id: ComponentId) -> Option<&HashSet> { self.components.get(id.0).map(|info| &info.required_by) } #[inline] pub(crate) fn get_required_by_mut( &mut self, id: ComponentId, ) -> Option<&mut HashSet> { self.components .get_mut(id.0) .map(|info| &mut info.required_by) } /// Type-erased equivalent of [`Components::component_id()`]. #[inline] pub fn get_id(&self, type_id: TypeId) -> Option { self.indices.get(&type_id).copied() } /// Returns the [`ComponentId`] of the given [`Component`] type `T`. /// /// The returned `ComponentId` is specific to the `Components` instance /// it was retrieved from and should not be used with another `Components` /// instance. /// /// Returns [`None`] if the `Component` type has not /// yet been initialized using [`Components::register_component()`]. /// /// ``` /// use bevy_ecs::prelude::*; /// /// let mut world = World::new(); /// /// #[derive(Component)] /// struct ComponentA; /// /// let component_a_id = world.register_component::(); /// /// assert_eq!(component_a_id, world.components().component_id::().unwrap()) /// ``` /// /// # See also /// /// * [`Components::get_id()`] /// * [`Components::resource_id()`] /// * [`World::component_id()`] #[inline] pub fn component_id(&self) -> Option { self.get_id(TypeId::of::()) } /// Type-erased equivalent of [`Components::resource_id()`]. #[inline] pub fn get_resource_id(&self, type_id: TypeId) -> Option { self.resource_indices.get(&type_id).copied() } /// Returns the [`ComponentId`] of the given [`Resource`] type `T`. /// /// The returned `ComponentId` is specific to the `Components` instance /// it was retrieved from and should not be used with another `Components` /// instance. /// /// Returns [`None`] if the `Resource` type has not /// yet been initialized using [`Components::register_resource()`]. /// /// ``` /// use bevy_ecs::prelude::*; /// /// let mut world = World::new(); /// /// #[derive(Resource, Default)] /// struct ResourceA; /// /// let resource_a_id = world.init_resource::(); /// /// assert_eq!(resource_a_id, world.components().resource_id::().unwrap()) /// ``` /// /// # See also /// /// * [`Components::component_id()`] /// * [`Components::get_resource_id()`] #[inline] pub fn resource_id(&self) -> Option { self.get_resource_id(TypeId::of::()) } /// Registers a [`Resource`] of type `T` with this instance. /// If a resource of this type has already been registered, this will return /// the ID of the pre-existing resource. /// /// # See also /// /// * [`Components::resource_id()`] /// * [`Components::register_resource_with_descriptor()`] #[inline] pub fn register_resource(&mut self) -> ComponentId { // SAFETY: The [`ComponentDescriptor`] matches the [`TypeId`] unsafe { self.get_or_register_resource_with(TypeId::of::(), || { ComponentDescriptor::new_resource::() }) } } /// Registers a [`Resource`] described by `descriptor`. /// /// # Note /// /// If this method is called multiple times with identical descriptors, a distinct [`ComponentId`] /// will be created for each one. /// /// # See also /// /// * [`Components::resource_id()`] /// * [`Components::register_resource()`] pub fn register_resource_with_descriptor( &mut self, descriptor: ComponentDescriptor, ) -> ComponentId { Components::register_resource_inner(&mut self.components, descriptor) } /// Registers a [non-send resource](crate::system::NonSend) of type `T` with this instance. /// If a resource of this type has already been registered, this will return /// the ID of the pre-existing resource. #[inline] pub fn register_non_send(&mut self) -> ComponentId { // SAFETY: The [`ComponentDescriptor`] matches the [`TypeId`] unsafe { self.get_or_register_resource_with(TypeId::of::(), || { ComponentDescriptor::new_non_send::(StorageType::default()) }) } } /// # Safety /// /// The [`ComponentDescriptor`] must match the [`TypeId`] #[inline] unsafe fn get_or_register_resource_with( &mut self, type_id: TypeId, func: impl FnOnce() -> ComponentDescriptor, ) -> ComponentId { let components = &mut self.components; *self.resource_indices.entry(type_id).or_insert_with(|| { let descriptor = func(); Components::register_resource_inner(components, descriptor) }) } #[inline] fn register_resource_inner( components: &mut Vec, descriptor: ComponentDescriptor, ) -> ComponentId { let component_id = ComponentId(components.len()); components.push(ComponentInfo::new(component_id, descriptor)); component_id } /// Gets an iterator over all components registered with this instance. pub fn iter(&self) -> impl Iterator + '_ { self.components.iter() } } /// A value that tracks when a system ran relative to other systems. /// This is used to power change detection. /// /// *Note* that a system that hasn't been run yet has a `Tick` of 0. #[derive(Copy, Clone, Default, Debug, Eq, Hash, PartialEq)] #[cfg_attr( feature = "bevy_reflect", derive(Reflect), reflect(Debug, Hash, PartialEq) )] pub struct Tick { tick: u32, } impl Tick { /// The maximum relative age for a change tick. /// The value of this is equal to [`MAX_CHANGE_AGE`]. /// /// Since change detection will not work for any ticks older than this, /// ticks are periodically scanned to ensure their relative values are below this. pub const MAX: Self = Self::new(MAX_CHANGE_AGE); /// Creates a new [`Tick`] wrapping the given value. #[inline] pub const fn new(tick: u32) -> Self { Self { tick } } /// Gets the value of this change tick. #[inline] pub const fn get(self) -> u32 { self.tick } /// Sets the value of this change tick. #[inline] pub fn set(&mut self, tick: u32) { self.tick = tick; } /// Returns `true` if this `Tick` occurred since the system's `last_run`. /// /// `this_run` is the current tick of the system, used as a reference to help deal with wraparound. #[inline] pub fn is_newer_than(self, last_run: Tick, this_run: Tick) -> bool { // This works even with wraparound because the world tick (`this_run`) is always "newer" than // `last_run` and `self.tick`, and we scan periodically to clamp `ComponentTicks` values // so they never get older than `u32::MAX` (the difference would overflow). // // The clamp here ensures determinism (since scans could differ between app runs). let ticks_since_insert = this_run.relative_to(self).tick.min(MAX_CHANGE_AGE); let ticks_since_system = this_run.relative_to(last_run).tick.min(MAX_CHANGE_AGE); ticks_since_system > ticks_since_insert } /// Returns a change tick representing the relationship between `self` and `other`. #[inline] pub(crate) fn relative_to(self, other: Self) -> Self { let tick = self.tick.wrapping_sub(other.tick); Self { tick } } /// Wraps this change tick's value if it exceeds [`Tick::MAX`]. /// /// Returns `true` if wrapping was performed. Otherwise, returns `false`. #[inline] pub(crate) fn check_tick(&mut self, tick: Tick) -> bool { let age = tick.relative_to(*self); // This comparison assumes that `age` has not overflowed `u32::MAX` before, which will be true // so long as this check always runs before that can happen. if age.get() > Self::MAX.get() { *self = tick.relative_to(Self::MAX); true } else { false } } } /// Interior-mutable access to the [`Tick`]s for a single component or resource. #[derive(Copy, Clone, Debug)] pub struct TickCells<'a> { /// The tick indicating when the value was added to the world. pub added: &'a UnsafeCell, /// The tick indicating the last time the value was modified. pub changed: &'a UnsafeCell, } impl<'a> TickCells<'a> { /// # Safety /// All cells contained within must uphold the safety invariants of [`UnsafeCellDeref::read`]. #[inline] pub(crate) unsafe fn read(&self) -> ComponentTicks { ComponentTicks { // SAFETY: The callers uphold the invariants for `read`. added: unsafe { self.added.read() }, // SAFETY: The callers uphold the invariants for `read`. changed: unsafe { self.changed.read() }, } } } /// Records when a component or resource was added and when it was last mutably dereferenced (or added). #[derive(Copy, Clone, Debug)] #[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Debug))] pub struct ComponentTicks { /// Tick recording the time this component or resource was added. pub added: Tick, /// Tick recording the time this component or resource was most recently changed. pub changed: Tick, } impl ComponentTicks { /// Returns `true` if the component or resource was added after the system last ran /// (or the system is running for the first time). #[inline] pub fn is_added(&self, last_run: Tick, this_run: Tick) -> bool { self.added.is_newer_than(last_run, this_run) } /// Returns `true` if the component or resource was added or mutably dereferenced after the system last ran /// (or the system is running for the first time). #[inline] pub fn is_changed(&self, last_run: Tick, this_run: Tick) -> bool { self.changed.is_newer_than(last_run, this_run) } /// Creates a new instance with the same change tick for `added` and `changed`. pub fn new(change_tick: Tick) -> Self { Self { added: change_tick, changed: change_tick, } } /// Manually sets the change tick. /// /// This is normally done automatically via the [`DerefMut`](std::ops::DerefMut) implementation /// on [`Mut`](crate::change_detection::Mut), [`ResMut`](crate::change_detection::ResMut), etc. /// However, components and resources that make use of interior mutability might require manual updates. /// /// # Example /// ```no_run /// # use bevy_ecs::{world::World, component::ComponentTicks}; /// let world: World = unimplemented!(); /// let component_ticks: ComponentTicks = unimplemented!(); /// /// component_ticks.set_changed(world.read_change_tick()); /// ``` #[inline] pub fn set_changed(&mut self, change_tick: Tick) { self.changed = change_tick; } } /// A [`SystemParam`] that provides access to the [`ComponentId`] for a specific component type. /// /// # Example /// ``` /// # use bevy_ecs::{system::Local, component::{Component, ComponentId, ComponentIdFor}}; /// #[derive(Component)] /// struct Player; /// fn my_system(component_id: ComponentIdFor) { /// let component_id: ComponentId = component_id.get(); /// // ... /// } /// ``` #[derive(SystemParam)] pub struct ComponentIdFor<'s, T: Component>(Local<'s, InitComponentId>); impl ComponentIdFor<'_, T> { /// Gets the [`ComponentId`] for the type `T`. #[inline] pub fn get(&self) -> ComponentId { **self } } impl core::ops::Deref for ComponentIdFor<'_, T> { type Target = ComponentId; fn deref(&self) -> &Self::Target { &self.0.component_id } } impl From> for ComponentId { #[inline] fn from(to_component_id: ComponentIdFor) -> ComponentId { *to_component_id } } /// Initializes the [`ComponentId`] for a specific type when used with [`FromWorld`]. struct InitComponentId { component_id: ComponentId, marker: PhantomData, } impl FromWorld for InitComponentId { fn from_world(world: &mut World) -> Self { Self { component_id: world.register_component::(), marker: PhantomData, } } } /// An error returned when the registration of a required component fails. #[derive(Error, Debug)] #[non_exhaustive] pub enum RequiredComponentsError { /// The component is already a directly required component for the requiree. #[error("Component {0:?} already directly requires component {1:?}")] DuplicateRegistration(ComponentId, ComponentId), /// An archetype with the component that requires other components already exists #[error("An archetype with the component {0:?} that requires other components already exists")] ArchetypeExists(ComponentId), } /// A Required Component constructor. See [`Component`] for details. #[derive(Clone)] pub struct RequiredComponentConstructor( pub Arc, ); impl RequiredComponentConstructor { /// # Safety /// This is intended to only be called in the context of [`BundleInfo::write_components`] to initialized required components. /// Calling it _anywhere else_ should be considered unsafe. /// /// `table_row` and `entity` must correspond to a valid entity that currently needs a component initialized via the constructor stored /// on this [`RequiredComponentConstructor`]. The stored constructor must correspond to a component on `entity` that needs initialization. /// `table` and `sparse_sets` must correspond to storages on a world where `entity` needs this required component initialized. /// /// Again, don't call this anywhere but [`BundleInfo::write_components`]. pub(crate) unsafe fn initialize( &self, table: &mut Table, sparse_sets: &mut SparseSets, change_tick: Tick, table_row: TableRow, entity: Entity, caller: MaybeLocation, ) { (self.0)(table, sparse_sets, change_tick, table_row, entity, caller); } } /// Metadata associated with a required component. See [`Component`] for details. #[derive(Clone)] pub struct RequiredComponent { /// The constructor used for the required component. pub constructor: RequiredComponentConstructor, /// The depth of the component requirement in the requirement hierarchy for this component. /// This is used for determining which constructor is used in cases where there are duplicate requires. /// /// For example, consider the inheritance tree `X -> Y -> Z`, where `->` indicates a requirement. /// `X -> Y` and `Y -> Z` are direct requirements with a depth of 0, while `Z` is only indirectly /// required for `X` with a depth of `1`. /// /// In cases where there are multiple conflicting requirements with the same depth, a higher priority /// will be given to components listed earlier in the `require` attribute, or to the latest added requirement /// if registered at runtime. pub inheritance_depth: u16, } /// The collection of metadata for components that are required for a given component. /// /// For more information, see the "Required Components" section of [`Component`]. #[derive(Default, Clone)] pub struct RequiredComponents(pub(crate) HashMap); impl Debug for RequiredComponents { fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { f.debug_tuple("RequiredComponents") .field(&self.0.keys()) .finish() } } impl RequiredComponents { /// Registers a required component. /// /// If the component is already registered, it will be overwritten if the given inheritance depth /// is smaller than the depth of the existing registration. Otherwise, the new registration will be ignored. /// /// # Safety /// /// `component_id` must match the type initialized by `constructor`. /// `constructor` _must_ initialize a component for `component_id` in such a way that /// matches the storage type of the component. It must only use the given `table_row` or `Entity` to /// initialize the storage for `component_id` corresponding to the given entity. pub unsafe fn register_dynamic( &mut self, component_id: ComponentId, constructor: RequiredComponentConstructor, inheritance_depth: u16, ) { self.0 .entry(component_id) .and_modify(|component| { if component.inheritance_depth > inheritance_depth { // New registration is more specific than existing requirement component.constructor = constructor.clone(); component.inheritance_depth = inheritance_depth; } }) .or_insert(RequiredComponent { constructor, inheritance_depth, }); } /// Registers a required component. /// /// If the component is already registered, it will be overwritten if the given inheritance depth /// is smaller than the depth of the existing registration. Otherwise, the new registration will be ignored. pub fn register( &mut self, components: &mut Components, constructor: fn() -> C, inheritance_depth: u16, ) { let component_id = components.register_component::(); self.register_by_id(component_id, constructor, inheritance_depth); } /// Registers the [`Component`] with the given ID as required if it exists. /// /// If the component is already registered, it will be overwritten if the given inheritance depth /// is smaller than the depth of the existing registration. Otherwise, the new registration will be ignored. pub fn register_by_id( &mut self, component_id: ComponentId, constructor: fn() -> C, inheritance_depth: u16, ) { let erased: RequiredComponentConstructor = RequiredComponentConstructor({ // `portable-atomic-util` `Arc` is not able to coerce an unsized // type like `std::sync::Arc` can. Creating a `Box` first does the // coercion. // // This would be resolved by https://github.com/rust-lang/rust/issues/123430 #[cfg(not(target_has_atomic = "ptr"))] use alloc::boxed::Box; type Constructor = dyn for<'a, 'b> Fn( &'a mut Table, &'b mut SparseSets, Tick, TableRow, Entity, MaybeLocation, ); #[cfg(not(target_has_atomic = "ptr"))] type Intermediate = Box; #[cfg(target_has_atomic = "ptr")] type Intermediate = Arc; let boxed: Intermediate = Intermediate::new( move |table, sparse_sets, change_tick, table_row, entity, caller| { OwningPtr::make(constructor(), |ptr| { // SAFETY: This will only be called in the context of `BundleInfo::write_components`, which will // pass in a valid table_row and entity requiring a C constructor // C::STORAGE_TYPE is the storage type associated with `component_id` / `C` // `ptr` points to valid `C` data, which matches the type associated with `component_id` unsafe { BundleInfo::initialize_required_component( table, sparse_sets, change_tick, table_row, entity, component_id, C::STORAGE_TYPE, ptr, caller, ); } }); }, ); Arc::from(boxed) }); // SAFETY: // `component_id` matches the type initialized by the `erased` constructor above. // `erased` initializes a component for `component_id` in such a way that // matches the storage type of the component. It only uses the given `table_row` or `Entity` to // initialize the storage corresponding to the given entity. unsafe { self.register_dynamic(component_id, erased, inheritance_depth) }; } /// Iterates the ids of all required components. This includes recursive required components. pub fn iter_ids(&self) -> impl Iterator + '_ { self.0.keys().copied() } /// Removes components that are explicitly provided in a given [`Bundle`]. These components should /// be logically treated as normal components, not "required components". /// /// [`Bundle`]: crate::bundle::Bundle pub(crate) fn remove_explicit_components(&mut self, components: &[ComponentId]) { for component in components { self.0.remove(component); } } // Merges `required_components` into this collection. This only inserts a required component // if it _did not already exist_. pub(crate) fn merge(&mut self, required_components: &RequiredComponents) { for (id, constructor) in &required_components.0 { self.0.entry(*id).or_insert_with(|| constructor.clone()); } } } // NOTE: This should maybe be private, but it is currently public so that `bevy_ecs_macros` can use it. // This exists as a standalone function instead of being inlined into the component derive macro so as // to reduce the amount of generated code. #[doc(hidden)] pub fn enforce_no_required_components_recursion( components: &Components, recursion_check_stack: &[ComponentId], ) { if let Some((&requiree, check)) = recursion_check_stack.split_last() { if let Some(direct_recursion) = check .iter() .position(|&id| id == requiree) .map(|index| index == check.len() - 1) { panic!( "Recursive required components detected: {}\nhelp: {}", recursion_check_stack .iter() .map(|id| format!("{}", ShortName(components.get_name(*id).unwrap()))) .collect::>() .join(" → "), if direct_recursion { format!( "Remove require({}).", ShortName(components.get_name(requiree).unwrap()) ) } else { "If this is intentional, consider merging the components.".into() } ); } } } /// Component [clone handler function](ComponentCloneFn) implemented using the [`Clone`] trait. /// Can be [set](Component::clone_behavior) as clone handler for the specific component it is implemented for. /// It will panic if set as handler for any other component. /// pub fn component_clone_via_clone( _commands: &mut Commands, source: &SourceComponent, ctx: &mut ComponentCloneCtx, ) { if let Some(component) = source.read::() { ctx.write_target_component(component.clone()); } } /// Component [clone handler function](ComponentCloneFn) implemented using reflect. /// Can be [set](Component::clone_behavior) as clone handler for any registered component, /// but only reflected components will be cloned. /// /// To clone a component using this handler, the following must be true: /// - World has [`AppTypeRegistry`](crate::reflect::AppTypeRegistry) /// - Component has [`TypeId`] /// - Component is registered /// - Component has [`ReflectFromPtr`](bevy_reflect::ReflectFromPtr) registered /// - Component has one of the following registered: [`ReflectFromReflect`](bevy_reflect::ReflectFromReflect), /// [`ReflectDefault`](bevy_reflect::std_traits::ReflectDefault), [`ReflectFromWorld`](crate::reflect::ReflectFromWorld) /// /// If any of the conditions is not satisfied, the component will be skipped. /// /// See [`EntityClonerBuilder`](crate::entity::EntityClonerBuilder) for details. #[cfg(feature = "bevy_reflect")] pub fn component_clone_via_reflect( commands: &mut Commands, source: &SourceComponent, ctx: &mut ComponentCloneCtx, ) { let Some(app_registry) = ctx.type_registry().cloned() else { return; }; let registry = app_registry.read(); let Some(source_component_reflect) = source.read_reflect(®istry) else { return; }; let component_info = ctx.component_info(); // checked in read_source_component_reflect let type_id = component_info.type_id().unwrap(); // Try to clone using ReflectFromReflect if let Some(reflect_from_reflect) = registry.get_type_data::(type_id) { if let Some(mut component) = reflect_from_reflect.from_reflect(source_component_reflect.as_partial_reflect()) { if let Some(reflect_component) = registry.get_type_data::(type_id) { reflect_component.visit_entities_mut(&mut *component, &mut |entity| { *entity = ctx.entity_mapper().get_mapped(*entity); }); } drop(registry); ctx.write_target_component_reflect(component); return; } } // Else, try to clone using ReflectDefault if let Some(reflect_default) = registry.get_type_data::(type_id) { let mut component = reflect_default.default(); component.apply(source_component_reflect.as_partial_reflect()); drop(registry); ctx.write_target_component_reflect(component); return; } // Otherwise, try to clone using ReflectFromWorld if let Some(reflect_from_world) = registry.get_type_data::(type_id) { let reflect_from_world = reflect_from_world.clone(); let mut mapped_entities = Vec::new(); if let Some(reflect_component) = registry.get_type_data::(type_id) { reflect_component.visit_entities(source_component_reflect, &mut |entity| { mapped_entities.push(entity); }); } let source_component_cloned = source_component_reflect.clone_value(); let component_layout = component_info.layout(); let target = ctx.target(); let component_id = ctx.component_id(); for entity in mapped_entities.iter_mut() { *entity = ctx.entity_mapper().get_mapped(*entity); } drop(registry); commands.queue(move |world: &mut World| { let mut component = reflect_from_world.from_world(world); assert_eq!(type_id, (*component).type_id()); component.apply(source_component_cloned.as_partial_reflect()); if let Some(reflect_component) = app_registry .read() .get_type_data::(type_id) { let mut i = 0; reflect_component.visit_entities_mut(&mut *component, &mut |entity| { *entity = mapped_entities[i]; i += 1; }); } // SAFETY: // - component_id is from the same world as target entity // - component is a valid value represented by component_id unsafe { let raw_component_ptr = core::ptr::NonNull::new_unchecked(Box::into_raw(component).cast::()); world .entity_mut(target) .insert_by_id(component_id, OwningPtr::new(raw_component_ptr)); alloc::alloc::dealloc(raw_component_ptr.as_ptr(), component_layout); } }); } } /// Noop implementation of component clone handler function. /// /// See [`EntityClonerBuilder`](crate::entity::EntityClonerBuilder) for details. pub fn component_clone_ignore( _commands: &mut Commands, _source: &SourceComponent, _ctx: &mut ComponentCloneCtx, ) { } /// Wrapper for components clone specialization using autoderef. #[doc(hidden)] pub struct DefaultCloneBehaviorSpecialization(PhantomData); impl Default for DefaultCloneBehaviorSpecialization { fn default() -> Self { Self(PhantomData) } } /// Base trait for components clone specialization using autoderef. #[doc(hidden)] pub trait DefaultCloneBehaviorBase { fn default_clone_behavior(&self) -> ComponentCloneBehavior; } impl DefaultCloneBehaviorBase for DefaultCloneBehaviorSpecialization { fn default_clone_behavior(&self) -> ComponentCloneBehavior { ComponentCloneBehavior::Default } } /// Specialized trait for components clone specialization using autoderef. #[doc(hidden)] pub trait DefaultCloneBehaviorViaClone { fn default_clone_behavior(&self) -> ComponentCloneBehavior; } impl DefaultCloneBehaviorViaClone for &DefaultCloneBehaviorSpecialization { fn default_clone_behavior(&self) -> ComponentCloneBehavior { ComponentCloneBehavior::clone::() } }