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# Objective Fix #4278 Fix #5504 Fix #9422 Provide safe ways to borrow an entire entity, while allowing disjoint mutable access. `EntityRef` and `EntityMut` are not suitable for this, since they provide access to the entire world -- they are just helper types for working with `&World`/`&mut World`. This has potential uses for reflection and serialization ## Solution Remove `EntityRef::world`, which allows it to soundly be used within queries. `EntityMut` no longer supports structural world mutations, which allows multiple instances of it to exist for different entities at once. Structural world mutations are performed using the new type `EntityWorldMut`. ```rust fn disjoint_system( q2: Query<&mut A>, q1: Query<EntityMut, Without<A>>, ) { ... } let [entity1, entity2] = world.many_entities_mut([id1, id2]); *entity1.get_mut::<T>().unwrap() = *entity2.get().unwrap(); for entity in world.iter_entities_mut() { ... } ``` --- ## Changelog - Removed `EntityRef::world`, to fix a soundness issue with queries. + Removed the ability to structurally mutate the world using `EntityMut`, which allows it to be used in queries. + Added `EntityWorldMut`, which is used to perform structural mutations that are no longer allowed using `EntityMut`. ## Migration Guide **Note for maintainers: ensure that the guide for #9604 is updated accordingly.** Removed the method `EntityRef::world`, to fix a soundness issue with queries. If you need access to `&World` while using an `EntityRef`, consider passing the world as a separate parameter. `EntityMut` can no longer perform 'structural' world mutations, such as adding or removing components, or despawning the entity. Additionally, `EntityMut::world`, `EntityMut::world_mut` , and `EntityMut::world_scope` have been removed. Instead, use the newly-added type `EntityWorldMut`, which is a helper type for working with `&mut World`. --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> |
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