[Merged by Bors] - Remove ExclusiveSystemParam::apply
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joseph-gio
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I'm in favor of removing this footgun. |
alice-i-cecile
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Feb 3, 2023
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bors r+ |
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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.
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ExclusiveSystemParam::applyExclusiveSystemParam::apply
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Objective
The trait method
SystemParam::applyallows aSystemParamtype to defer world mutations, which is internally used to applyCommandsat the end of the stage. Any operations that require&mut Worldaccess must be deferred in this way, since parallel systems do not have exclusive access to the world.The
ExclusiveSystemParamtrait (added in #6083) has anapplymethod which serves the same purpose. However, deferring mutations in this way does not make sense for exclusive systems since they already have&mut Worldaccess: 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.
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::applyhas 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.