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Emphasize no structural changes in SystemParam::get_param #17996

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merged 6 commits into from
Mar 4, 2025
Merged

Emphasize no structural changes in SystemParam::get_param #17996

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b0a253b
Emphasize no structural changes in SystemParam::get_param
GlennFolker Feb 23, 2025
a37bc17
Add more docs
GlennFolker Feb 24, 2025
f842d91
`cargo fmt --all`
GlennFolker Feb 24, 2025
02d5d80
Merge branch 'main' into get-param-safety
GlennFolker Feb 24, 2025
7f340d9
Merge remote-tracking branch 'upstream/main' into get-param-safety
GlennFolker Mar 4, 2025
801cf28
Just document UnsafeWorldCell
GlennFolker Mar 4, 2025
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14 changes: 11 additions & 3 deletions crates/bevy_ecs/src/system/system_param.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -180,6 +180,9 @@ use variadics_please::{all_tuples, all_tuples_enumerated};
/// The implementor must ensure the following is true.
/// - [`SystemParam::init_state`] correctly registers all [`World`] accesses used
/// by [`SystemParam::get_param`] with the provided [`system_meta`](SystemMeta).
/// - [`SystemParam::get_param`] does **not** make any structural ECS changes in the
/// [`World`], e.g. [`World::spawn`], [`World::register_component`], and other similar
/// methods. In case that's necessary, do that in [`SystemParam::init_state`] instead.
/// - None of the world accesses may conflict with any prior accesses registered
/// on `system_meta`.
pub unsafe trait SystemParam: Sized {
Expand Down Expand Up @@ -274,12 +277,17 @@ pub unsafe trait SystemParam: Sized {

/// Creates a parameter to be passed into a [`SystemParamFunction`](super::SystemParamFunction).
///
/// This method guarantees no structural ECS changes to the `world`, which effectively acts like
/// [`DeferredWorld`] with unsafe accesses to everything requested in [`SystemParam::init_state`].
/// This allows, for example (but not limited to), invoking `get_param` in multiple systems to
/// the same world concurrently, provided all mutable accesses are disjoint.
///
/// # Safety
///
/// - The passed [`UnsafeWorldCell`] must have access to any world data
/// registered in [`init_state`](SystemParam::init_state).
/// - The passed [`UnsafeWorldCell`] must have access to any world data registered
/// in [`init_state`](SystemParam::init_state).
/// - `world` must be the same [`World`] that was used to initialize [`state`](SystemParam::init_state).
/// - all `world`'s archetypes have been processed by [`new_archetype`](SystemParam::new_archetype).
/// - All `world`'s archetypes have been processed by [`new_archetype`](SystemParam::new_archetype).
unsafe fn get_param<'world, 'state>(
state: &'state mut Self::State,
system_meta: &SystemMeta,
Expand Down