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# Objective First of all, this PR took heavy inspiration from #7760 and #5715. It intends to also fix #5569, but with a slightly different approach. This also fixes #9335 by reexporting `DynEq`. ## Solution The advantage of this API is that we can intern a value without allocating for zero-sized-types and for enum variants that have no fields. This PR does this automatically in the `SystemSet` and `ScheduleLabel` derive macros for unit structs and fieldless enum variants. So this should cover many internal and external use cases of `SystemSet` and `ScheduleLabel`. In these optimal use cases, no memory will be allocated. - The interning returns a `Interned<dyn SystemSet>`, which is just a wrapper around a `&'static dyn SystemSet`. - `Hash` and `Eq` are implemented in terms of the pointer value of the reference, similar to my first approach of anonymous system sets in #7676. - Therefore, `Interned<T>` does not implement `Borrow<T>`, only `Deref`. - The debug output of `Interned<T>` is the same as the interned value. Edit: - `AppLabel` is now also interned and the old `derive_label`/`define_label` macros were replaced with the new interning implementation. - Anonymous set ids are reused for different `Schedule`s, reducing the amount of leaked memory. ### Pros - `InternedSystemSet` and `InternedScheduleLabel` behave very similar to the current `BoxedSystemSet` and `BoxedScheduleLabel`, but can be copied without an allocation. - Many use cases don't allocate at all. - Very fast lookups and comparisons when using `InternedSystemSet` and `InternedScheduleLabel`. - The `intern` module might be usable in other areas. - `Interned{ScheduleLabel, SystemSet, AppLabel}` does implement `{ScheduleLabel, SystemSet, AppLabel}`, increasing ergonomics. ### Cons - Implementors of `SystemSet` and `ScheduleLabel` still need to implement `Hash` and `Eq` (and `Clone`) for it to work. ## Changelog ### Added - Added `intern` module to `bevy_utils`. - Added reexports of `DynEq` to `bevy_ecs` and `bevy_app`. ### Changed - Replaced `BoxedSystemSet` and `BoxedScheduleLabel` with `InternedSystemSet` and `InternedScheduleLabel`. - Replaced `impl AsRef<dyn ScheduleLabel>` with `impl ScheduleLabel`. - Replaced `AppLabelId` with `InternedAppLabel`. - Changed `AppLabel` to use `Debug` for error messages. - Changed `AppLabel` to use interning. - Changed `define_label`/`derive_label` to use interning. - Replaced `define_boxed_label`/`derive_boxed_label` with `define_label`/`derive_label`. - Changed anonymous set ids to be only unique inside a schedule, not globally. - Made interned label types implement their label trait. ### Removed - Removed `define_boxed_label` and `derive_boxed_label`. ## Migration guide - Replace `BoxedScheduleLabel` and `Box<dyn ScheduleLabel>` with `InternedScheduleLabel` or `Interned<dyn ScheduleLabel>`. - Replace `BoxedSystemSet` and `Box<dyn SystemSet>` with `InternedSystemSet` or `Interned<dyn SystemSet>`. - Replace `AppLabelId` with `InternedAppLabel` or `Interned<dyn AppLabel>`. - Types manually implementing `ScheduleLabel`, `AppLabel` or `SystemSet` need to implement: - `dyn_hash` directly instead of implementing `DynHash` - `as_dyn_eq` - Pass labels to `World::try_schedule_scope`, `World::schedule_scope`, `World::try_run_schedule`. `World::run_schedule`, `Schedules::remove`, `Schedules::remove_entry`, `Schedules::contains`, `Schedules::get` and `Schedules::get_mut` by value instead of by reference. --------- Co-authored-by: Joseph <21144246+JoJoJet@users.noreply.github.com> Co-authored-by: Carter Anderson <mcanders1@gmail.com> |
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