bevy_ecs/world/entity_fetch.rs
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use core::mem::MaybeUninit;
use crate::{
entity::{Entity, EntityHash, EntityHashMap, EntityHashSet},
world::{
error::EntityFetchError, unsafe_world_cell::UnsafeWorldCell, EntityMut, EntityRef,
EntityWorldMut,
},
};
/// Types that can be used to fetch [`Entity`] references from a [`World`].
///
/// Provided implementations are:
/// - [`Entity`]: Fetch a single entity.
/// - `[Entity; N]`/`&[Entity; N]`: Fetch multiple entities, receiving a
/// same-sized array of references.
/// - `&[Entity]`: Fetch multiple entities, receiving a vector of references.
/// - [`&EntityHashSet`](EntityHashSet): Fetch multiple entities, receiving a
/// hash map of [`Entity`] IDs to references.
///
/// # Performance
///
/// - The slice and array implementations perform an aliased mutabiltiy check
/// in [`WorldEntityFetch::fetch_mut`] that is `O(N^2)`.
/// - The [`EntityHashSet`] implementation performs no such check as the type
/// itself guarantees no duplicates.
/// - The single [`Entity`] implementation performs no such check as only one
/// reference is returned.
///
/// # Safety
///
/// Implementor must ensure that:
/// - No aliased mutability is caused by the returned references.
/// - [`WorldEntityFetch::fetch_ref`] returns only read-only references.
/// - [`WorldEntityFetch::fetch_deferred_mut`] returns only non-structurally-mutable references.
///
/// [`World`]: crate::world::World
pub unsafe trait WorldEntityFetch {
/// The read-only reference type returned by [`WorldEntityFetch::fetch_ref`].
type Ref<'w>;
/// The mutable reference type returned by [`WorldEntityFetch::fetch_mut`].
type Mut<'w>;
/// The mutable reference type returned by [`WorldEntityFetch::fetch_deferred_mut`],
/// but without structural mutability.
type DeferredMut<'w>;
/// Returns read-only reference(s) to the entities with the given
/// [`Entity`] IDs, as determined by `self`.
///
/// # Safety
///
/// It is the caller's responsibility to ensure that:
/// - The given [`UnsafeWorldCell`] has read-only access to the fetched entities.
/// - No other mutable references to the fetched entities exist at the same time.
///
/// # Errors
///
/// - Returns [`Entity`] if the entity does not exist.
unsafe fn fetch_ref(self, cell: UnsafeWorldCell<'_>) -> Result<Self::Ref<'_>, Entity>;
/// Returns mutable reference(s) to the entities with the given [`Entity`]
/// IDs, as determined by `self`.
///
/// # Safety
///
/// It is the caller's responsibility to ensure that:
/// - The given [`UnsafeWorldCell`] has mutable access to the fetched entities.
/// - No other references to the fetched entities exist at the same time.
///
/// # Errors
///
/// - Returns [`EntityFetchError::NoSuchEntity`] if the entity does not exist.
/// - Returns [`EntityFetchError::AliasedMutability`] if the entity was
/// requested mutably more than once.
unsafe fn fetch_mut(self, cell: UnsafeWorldCell<'_>)
-> Result<Self::Mut<'_>, EntityFetchError>;
/// Returns mutable reference(s) to the entities with the given [`Entity`]
/// IDs, as determined by `self`, but without structural mutability.
///
/// No structural mutability means components cannot be removed from the
/// entity, new components cannot be added to the entity, and the entity
/// cannot be despawned.
///
/// # Safety
///
/// It is the caller's responsibility to ensure that:
/// - The given [`UnsafeWorldCell`] has mutable access to the fetched entities.
/// - No other references to the fetched entities exist at the same time.
///
/// # Errors
///
/// - Returns [`EntityFetchError::NoSuchEntity`] if the entity does not exist.
/// - Returns [`EntityFetchError::AliasedMutability`] if the entity was
/// requested mutably more than once.
unsafe fn fetch_deferred_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::DeferredMut<'_>, EntityFetchError>;
}
// SAFETY:
// - No aliased mutability is caused because a single reference is returned.
// - No mutable references are returned by `fetch_ref`.
// - No structurally-mutable references are returned by `fetch_deferred_mut`.
unsafe impl WorldEntityFetch for Entity {
type Ref<'w> = EntityRef<'w>;
type Mut<'w> = EntityWorldMut<'w>;
type DeferredMut<'w> = EntityMut<'w>;
unsafe fn fetch_ref(self, cell: UnsafeWorldCell<'_>) -> Result<Self::Ref<'_>, Entity> {
let ecell = cell.get_entity(self).ok_or(self)?;
// SAFETY: caller ensures that the world cell has read-only access to the entity.
Ok(unsafe { EntityRef::new(ecell) })
}
unsafe fn fetch_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::Mut<'_>, EntityFetchError> {
let location = cell
.entities()
.get(self)
.ok_or(EntityFetchError::NoSuchEntity(self))?;
// SAFETY: caller ensures that the world cell has mutable access to the entity.
let world = unsafe { cell.world_mut() };
// SAFETY: location was fetched from the same world's `Entities`.
Ok(unsafe { EntityWorldMut::new(world, self, location) })
}
unsafe fn fetch_deferred_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::DeferredMut<'_>, EntityFetchError> {
let ecell = cell
.get_entity(self)
.ok_or(EntityFetchError::NoSuchEntity(self))?;
// SAFETY: caller ensures that the world cell has mutable access to the entity.
Ok(unsafe { EntityMut::new(ecell) })
}
}
// SAFETY:
// - No aliased mutability is caused because the array is checked for duplicates.
// - No mutable references are returned by `fetch_ref`.
// - No structurally-mutable references are returned by `fetch_deferred_mut`.
unsafe impl<const N: usize> WorldEntityFetch for [Entity; N] {
type Ref<'w> = [EntityRef<'w>; N];
type Mut<'w> = [EntityMut<'w>; N];
type DeferredMut<'w> = [EntityMut<'w>; N];
unsafe fn fetch_ref(self, cell: UnsafeWorldCell<'_>) -> Result<Self::Ref<'_>, Entity> {
<&Self>::fetch_ref(&self, cell)
}
unsafe fn fetch_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::Mut<'_>, EntityFetchError> {
<&Self>::fetch_mut(&self, cell)
}
unsafe fn fetch_deferred_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::DeferredMut<'_>, EntityFetchError> {
<&Self>::fetch_deferred_mut(&self, cell)
}
}
// SAFETY:
// - No aliased mutability is caused because the array is checked for duplicates.
// - No mutable references are returned by `fetch_ref`.
// - No structurally-mutable references are returned by `fetch_deferred_mut`.
unsafe impl<const N: usize> WorldEntityFetch for &'_ [Entity; N] {
type Ref<'w> = [EntityRef<'w>; N];
type Mut<'w> = [EntityMut<'w>; N];
type DeferredMut<'w> = [EntityMut<'w>; N];
unsafe fn fetch_ref(self, cell: UnsafeWorldCell<'_>) -> Result<Self::Ref<'_>, Entity> {
let mut refs = [MaybeUninit::uninit(); N];
for (r, &id) in core::iter::zip(&mut refs, self) {
let ecell = cell.get_entity(id).ok_or(id)?;
// SAFETY: caller ensures that the world cell has read-only access to the entity.
*r = MaybeUninit::new(unsafe { EntityRef::new(ecell) });
}
// SAFETY: Each item was initialized in the loop above.
let refs = refs.map(|r| unsafe { MaybeUninit::assume_init(r) });
Ok(refs)
}
unsafe fn fetch_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::Mut<'_>, EntityFetchError> {
// Check for duplicate entities.
for i in 0..self.len() {
for j in 0..i {
if self[i] == self[j] {
return Err(EntityFetchError::AliasedMutability(self[i]));
}
}
}
let mut refs = [const { MaybeUninit::uninit() }; N];
for (r, &id) in core::iter::zip(&mut refs, self) {
let ecell = cell
.get_entity(id)
.ok_or(EntityFetchError::NoSuchEntity(id))?;
// SAFETY: caller ensures that the world cell has mutable access to the entity.
*r = MaybeUninit::new(unsafe { EntityMut::new(ecell) });
}
// SAFETY: Each item was initialized in the loop above.
let refs = refs.map(|r| unsafe { MaybeUninit::assume_init(r) });
Ok(refs)
}
unsafe fn fetch_deferred_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::DeferredMut<'_>, EntityFetchError> {
// SAFETY: caller ensures that the world cell has mutable access to the entity,
// and `fetch_mut` does not return structurally-mutable references.
unsafe { self.fetch_mut(cell) }
}
}
// SAFETY:
// - No aliased mutability is caused because the slice is checked for duplicates.
// - No mutable references are returned by `fetch_ref`.
// - No structurally-mutable references are returned by `fetch_deferred_mut`.
unsafe impl WorldEntityFetch for &'_ [Entity] {
type Ref<'w> = Vec<EntityRef<'w>>;
type Mut<'w> = Vec<EntityMut<'w>>;
type DeferredMut<'w> = Vec<EntityMut<'w>>;
unsafe fn fetch_ref(self, cell: UnsafeWorldCell<'_>) -> Result<Self::Ref<'_>, Entity> {
let mut refs = Vec::with_capacity(self.len());
for &id in self {
let ecell = cell.get_entity(id).ok_or(id)?;
// SAFETY: caller ensures that the world cell has read-only access to the entity.
refs.push(unsafe { EntityRef::new(ecell) });
}
Ok(refs)
}
unsafe fn fetch_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::Mut<'_>, EntityFetchError> {
// Check for duplicate entities.
for i in 0..self.len() {
for j in 0..i {
if self[i] == self[j] {
return Err(EntityFetchError::AliasedMutability(self[i]));
}
}
}
let mut refs = Vec::with_capacity(self.len());
for &id in self {
let ecell = cell
.get_entity(id)
.ok_or(EntityFetchError::NoSuchEntity(id))?;
// SAFETY: caller ensures that the world cell has mutable access to the entity.
refs.push(unsafe { EntityMut::new(ecell) });
}
Ok(refs)
}
unsafe fn fetch_deferred_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::DeferredMut<'_>, EntityFetchError> {
// SAFETY: caller ensures that the world cell has mutable access to the entity,
// and `fetch_mut` does not return structurally-mutable references.
unsafe { self.fetch_mut(cell) }
}
}
// SAFETY:
// - No aliased mutability is caused because `EntityHashSet` guarantees no duplicates.
// - No mutable references are returned by `fetch_ref`.
// - No structurally-mutable references are returned by `fetch_deferred_mut`.
unsafe impl WorldEntityFetch for &'_ EntityHashSet {
type Ref<'w> = EntityHashMap<EntityRef<'w>>;
type Mut<'w> = EntityHashMap<EntityMut<'w>>;
type DeferredMut<'w> = EntityHashMap<EntityMut<'w>>;
unsafe fn fetch_ref(self, cell: UnsafeWorldCell<'_>) -> Result<Self::Ref<'_>, Entity> {
let mut refs = EntityHashMap::with_capacity_and_hasher(self.len(), EntityHash);
for &id in self {
let ecell = cell.get_entity(id).ok_or(id)?;
// SAFETY: caller ensures that the world cell has read-only access to the entity.
refs.insert(id, unsafe { EntityRef::new(ecell) });
}
Ok(refs)
}
unsafe fn fetch_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::Mut<'_>, EntityFetchError> {
let mut refs = EntityHashMap::with_capacity_and_hasher(self.len(), EntityHash);
for &id in self {
let ecell = cell
.get_entity(id)
.ok_or(EntityFetchError::NoSuchEntity(id))?;
// SAFETY: caller ensures that the world cell has mutable access to the entity.
refs.insert(id, unsafe { EntityMut::new(ecell) });
}
Ok(refs)
}
unsafe fn fetch_deferred_mut(
self,
cell: UnsafeWorldCell<'_>,
) -> Result<Self::DeferredMut<'_>, EntityFetchError> {
// SAFETY: caller ensures that the world cell has mutable access to the entity,
// and `fetch_mut` does not return structurally-mutable references.
unsafe { self.fetch_mut(cell) }
}
}