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# Objective Follow-up to #6404 and #8292. Mutating the world through a shared reference is surprising, and it makes the meaning of `&World` unclear: sometimes it gives read-only access to the entire world, and sometimes it gives interior mutable access to only part of it. This is an up-to-date version of #6972. ## Solution Use `UnsafeWorldCell` for all interior mutability. Now, `&World` *always* gives you read-only access to the entire world. --- ## Changelog TODO - do we still care about changelogs? ## Migration Guide Mutating any world data using `&World` is now considered unsound -- the type `UnsafeWorldCell` must be used to achieve interior mutability. The following methods now accept `UnsafeWorldCell` instead of `&World`: - `QueryState`: `get_unchecked`, `iter_unchecked`, `iter_combinations_unchecked`, `for_each_unchecked`, `get_single_unchecked`, `get_single_unchecked_manual`. - `SystemState`: `get_unchecked_manual` ```rust let mut world = World::new(); let mut query = world.query::<&mut T>(); // Before: let t1 = query.get_unchecked(&world, entity_1); let t2 = query.get_unchecked(&world, entity_2); // After: let world_cell = world.as_unsafe_world_cell(); let t1 = query.get_unchecked(world_cell, entity_1); let t2 = query.get_unchecked(world_cell, entity_2); ``` The methods `QueryState::validate_world` and `SystemState::matches_world` now take a `WorldId` instead of `&World`: ```rust // Before: query_state.validate_world(&world); // After: query_state.validate_world(world.id()); ``` The methods `QueryState::update_archetypes` and `SystemState::update_archetypes` now take `UnsafeWorldCell` instead of `&World`: ```rust // Before: query_state.update_archetypes(&world); // After: query_state.update_archetypes(world.as_unsafe_world_cell_readonly()); ``` |
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