docs/bevy/release-content/migration-guides/function_systems.md 1.9 K · 36 lines · raw · history

1 ---
2 title: "Exclusive function systems have been unified with regular function systems"
3 pull_requests: [25507]
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5
6 `ExclusiveFunctionSystem`, `ExclusiveSystemParam`, and `ExclusiveSystemParamFunction`
7 have been removed. Exclusive function systems now use the same code path as
8 regular function systems: `FunctionSystem`, `SystemParam`, and `SystemParamFunction`.
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10 `&mut World` now implements `SystemParam`, which means it is no longer required
11 to be the first parameter of a function system. Instead, it may appear anywhere
12 in the parameter list, so long as it does not conflict with other system parameters
13 (same as before). Generally speaking, this means systems' "exclusivity" is now
14 tracked at runtime, rather than compile time.
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16 All `ExclusiveSystemParam`s that did not previously implement `SystemParam` now
17 implement it, including `&mut QueryState` and `&mut SystemState`.
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19 It is no longer possible to use `WorldId` in an exclusive system,
20 since the `SystemParam` implementation needs to read it from the `World`.
21 If you were using `WorldId` in an exclusive system,
22 consider calling `World::id()` as the first line of the system.
23 Alternately, use `Local<WorldId>` as a parameter,
24 which will be automatically populated with the correct ID.
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26 `System::is_exclusive()` has been removed. Use `SystemAccess::is_exclusive()` instead,
27 which is created by `System::initialize()` and stored in `SystemWithAccess`.
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29 `System::initialize()` now returns a `SystemAccess` rather than a `FilteredAccessSet`.
30 `SystemAccess` is a superset of `FilteredAccessSet` that also tracks whether the
31 system is exclusive, or requires no access to the world at all. If you require
32 access to a `FilteredAccessSet`, call `SystemAccess::require_shared_access(system_meta)`.
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34 `ExclusiveMarker` has been removed. If you need to mark a system as exclusive,
35 consider piping the system into a `fn(&mut World)` system, which will automatically
36 mark it as exclusive.