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Remove ExclusiveSystemParam::apply (#7489)

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# Objective

The trait method `SystemParam::apply` allows a `SystemParam` type to defer world mutations, which is internally used to apply `Commands` at the end of the stage. Any operations that require `&mut World` access must be deferred in this way, since parallel systems do not have exclusive access to the world.

The `ExclusiveSystemParam` trait (added in #6083) has an `apply` method which serves the same purpose. However, deferring mutations in this way does not make sense for exclusive systems since they already have `&mut World` access: there is no need to wait until a hard sync point, as the system *is* a hard sync point. World mutations can and should be performed within the body of the system.

## Solution

Remove the method. There were no implementations of this method in the engine.

---

## Changelog

*Note for maintainers: this changelog makes more sense if it's placed above the one for #6919.*

- Removed the method `ExclusiveSystemParamState::apply`.

## Migration Guide

*Note for maintainers: this migration guide makes more sense if it's placed above the one for #6919.*

The trait method `ExclusiveSystemParamState::apply` has been removed. If you have an exclusive system with buffers that must be applied, you should apply them within the body of the exclusive system.
This commit is contained in:
JoJoJet 2023-02-04 00:25:09 +00:00
parent 6506ea4d83
commit e0bf4311d3
2 changed files with 4 additions and 11 deletions
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7
crates/bevy_ecs/src/system/exclusive_function_system.rs
View file

@ -132,9 +132,10 @@ where
}
#[inline]
fn apply_buffers(&mut self, world: &mut World) {
let param_state = self.param_state.as_mut().expect(PARAM_MESSAGE);
Param::apply(param_state, world);
fn apply_buffers(&mut self, _world: &mut World) {
// "pure" exclusive systems do not have any buffers to apply.
// Systems made by piping a normal system with an exclusive system
// might have buffers to apply, but this is handled by `PipeSystem`.
}
#[inline]

8
crates/bevy_ecs/src/system/exclusive_system_param.rs
View file

@ -12,8 +12,6 @@ pub trait ExclusiveSystemParam: Sized {
type Item<'s>: ExclusiveSystemParam<State = Self::State>;
fn init(world: &mut World, system_meta: &mut SystemMeta) -> Self::State;
#[inline]
fn apply(_state: &mut Self::State, _world: &mut World) {}
fn get_param<'s>(state: &'s mut Self::State, system_meta: &SystemMeta) -> Self::Item<'s>;
}
@ -74,12 +72,6 @@ macro_rules! impl_exclusive_system_param_tuple {
(($($param::init(_world, _system_meta),)*))
}
#[inline]
fn apply(state: &mut Self::State, _world: &mut World) {
let ($($param,)*) = state;
$($param::apply($param, _world);)*
}
#[inline]
#[allow(clippy::unused_unit)]
fn get_param<'s>(