Turn apply_deferred into a ZST System
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bushrat011899
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Nice! I'm in favour of a breaking change to rename this ApplyDeferred. Users aren't supposed to actually call this as a function anyway, and giving it a PascalCase name should help highlight to users that it isn't a normal system.
Memory saving is also nice, especially since this system will be reused a lot in a typical application.
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# Objective - Required by bevyengine#16622 due to differing implementations of `System` by `FunctionSystem` and `ExclusiveFunctionSystem`. - Optimize the memory usage of instances of `apply_deferred` in system schedules. ## Solution By changing `apply_deferred` from being an ordinary system that ends up as an `ExclusiveFunctionSystem`, and instead into a ZST struct that implements `System` manually, we save ~320 bytes per instance of `apply_deferred` in any schedule. ## Testing - All current tests pass. --- ## Migration Guide - If you were previously calling the special `apply_deferred` system via `apply_deferred(world)`, don't.
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Objective
SystembyFunctionSystemandExclusiveFunctionSystem.apply_deferredin system schedules.Solution
By changing
apply_deferredfrom being an ordinary system that ends up as anExclusiveFunctionSystem, and instead into a ZST struct that implementsSystemmanually, we save ~320 bytes per instance ofapply_deferredin any schedule.Testing
Migration Guide
apply_deferredsystem viaapply_deferred(world), don't.