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# Objective Follow-up to #8030. Now that `SystemParam` and `WorldQuery` are implemented for `PhantomData`, the `ignore` attributes are now unnecessary. --- ## Changelog - Removed the attributes `#[system_param(ignore)]` and `#[world_query(ignore)]`. ## Migration Guide The attributes `#[system_param(ignore)]` and `#[world_query]` ignore have been removed. If you were using either of these with `PhantomData` fields, you can simply remove the attribute: ```rust #[derive(SystemParam)] struct MyParam<'w, 's, Marker> { ... // Before: #[system_param(ignore) _marker: PhantomData<Marker>, // After: _marker: PhantomData<Marker>, } #[derive(WorldQuery)] struct MyQuery<Marker> { ... // Before: #[world_query(ignore) _marker: PhantomData<Marker>, // After: _marker: PhantomData<Marker>, } ``` If you were using this for another type that implements `Default`, consider wrapping that type in `Local<>` (this only works for `SystemParam`): ```rust #[derive(SystemParam)] struct MyParam<'w, 's> { // Before: #[system_param(ignore)] value: MyDefaultType, // This will be initialized using `Default` each time `MyParam` is created. // After: value: Local<MyDefaultType>, // This will be initialized using `Default` the first time `MyParam` is created. } ``` If you are implementing either trait and need to preserve the exact behavior of the old `ignore` attributes, consider manually implementing `SystemParam` or `WorldQuery` for a wrapper struct that uses the `Default` trait: ```rust // Before: #[derive(WorldQuery) struct MyQuery { #[world_query(ignore)] str: String, } // After: #[derive(WorldQuery) struct MyQuery { str: DefaultQuery<String>, } pub struct DefaultQuery<T: Default>(pub T); unsafe impl<T: Default> WorldQuery for DefaultQuery<T> { type Item<'w> = Self; ... unsafe fn fetch<'w>(...) -> Self::Item<'w> { Self(T::default()) } } ``` |
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