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bevy/crates/bevy_ecs/src/system/system_param.rs
Chris Russell eee7fd5b3e
Encapsulate cfg(feature = "track_location") in a type. (#17602) 
# Objective

Eliminate the need to write `cfg(feature = "track_location")` every time
one uses an API that may use location tracking. It's verbose, and a
little intimidating. And it requires code outside of `bevy_ecs` that
wants to use location tracking needs to either unconditionally enable
the feature, or include conditional compilation of its own. It would be
good for users to be able to log locations when they are available
without needing to add feature flags to their own crates.

Reduce the number of cases where code compiles with the `track_location`
feature enabled, but not with it disabled, or vice versa. It can be hard
to remember to test it both ways!

Remove the need to store a `None` in `HookContext` when the
`track_location` feature is disabled.

## Solution

Create an `MaybeLocation<T>` type that contains a `T` if the
`track_location` feature is enabled, and is a ZST if it is not. The
overall API is similar to `Option`, but whether the value is `Some` or
`None` is set at compile time and is the same for all values.

Default `T` to `&'static Location<'static>`, since that is the most
common case.

Remove all `cfg(feature = "track_location")` blocks outside of the
implementation of that type, and instead call methods on it.

When `track_location` is disabled, `MaybeLocation` is a ZST and all
methods are `#[inline]` and empty, so they should be entirely removed by
the compiler. But the code will still be visible to the compiler and
checked, so if it compiles with the feature disabled then it should also
compile with it enabled, and vice versa.

## Open Questions

Where should these types live? I put them in `change_detection` because
that's where the existing `MaybeLocation` types were, but we now use
these outside of change detection.

While I believe that the compiler should be able to remove all of these
calls, I have not actually tested anything. If we want to take this
approach, what testing is required to ensure it doesn't impact
performance?

## Migration Guide

Methods like `Ref::changed_by()` that return a `&'static
Location<'static>` will now be available even when the `track_location`
feature is disabled, but they will return a new `MaybeLocation` type.
`MaybeLocation` wraps a `&'static Location<'static>` when the feature is
enabled, and is a ZST when the feature is disabled.

Existing code that needs a `&Location` can call `into_option().unwrap()`
to recover it. Many trait impls are forwarded, so if you only need
`Display` then no changes will be necessary.

If that code was conditionally compiled, you may instead want to use the
methods on `MaybeLocation` to remove the need for conditional
compilation.

Code that constructs a `Ref`, `Mut`, `Res`, or `ResMut` will now need to
provide location information unconditionally. If you are creating them
from existing Bevy types, you can obtain a `MaybeLocation` from methods
like `Table::get_changed_by_slice_for()` or
`ComponentSparseSet::get_with_ticks`. Otherwise, you will need to store
a `MaybeLocation` next to your data and use methods like `as_ref()` or
`as_mut()` to obtain wrapped references.
2025-02-10 21:21:20 +00:00

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pub use crate::change_detection::{NonSendMut, Res, ResMut};
use crate::{
archetype::{Archetype, Archetypes},
bundle::Bundles,
change_detection::{MaybeLocation, Ticks, TicksMut},
component::{ComponentId, ComponentTicks, Components, Tick},
entity::Entities,
query::{
Access, FilteredAccess, FilteredAccessSet, QueryData, QueryFilter, QuerySingleError,
QueryState, ReadOnlyQueryData,
},
resource::Resource,
storage::ResourceData,
system::{Query, Single, SystemMeta},
world::{
unsafe_world_cell::UnsafeWorldCell, DeferredWorld, FilteredResources, FilteredResourcesMut,
FromWorld, World,
},
};
use alloc::{borrow::ToOwned, boxed::Box, vec::Vec};
pub use bevy_ecs_macros::SystemParam;
use bevy_ptr::UnsafeCellDeref;
use bevy_utils::synccell::SyncCell;
use core::{
any::Any,
fmt::Debug,
marker::PhantomData,
ops::{Deref, DerefMut},
panic::Location,
};
use disqualified::ShortName;
use super::Populated;
use variadics_please::{all_tuples, all_tuples_enumerated};
/// A parameter that can be used in a [`System`](super::System).
///
/// # Derive
///
/// This trait can be derived with the [`derive@super::SystemParam`] macro.
/// This macro only works if each field on the derived struct implements [`SystemParam`].
/// Note: There are additional requirements on the field types.
/// See the *Generic `SystemParam`s* section for details and workarounds of the probable
/// cause if this derive causes an error to be emitted.
///
/// Derived `SystemParam` structs may have two lifetimes: `'w` for data stored in the [`World`],
/// and `'s` for data stored in the parameter's state.
///
/// The following list shows the most common [`SystemParam`]s and which lifetime they require
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource)]
/// # struct SomeResource;
/// # #[derive(Event)]
/// # struct SomeEvent;
/// # #[derive(Resource)]
/// # struct SomeOtherResource;
/// # use bevy_ecs::system::SystemParam;
/// # #[derive(SystemParam)]
/// # struct ParamsExample<'w, 's> {
/// # query:
/// Query<'w, 's, Entity>,
/// # res:
/// Res<'w, SomeResource>,
/// # res_mut:
/// ResMut<'w, SomeOtherResource>,
/// # local:
/// Local<'s, u8>,
/// # commands:
/// Commands<'w, 's>,
/// # eventreader:
/// EventReader<'w, 's, SomeEvent>,
/// # eventwriter:
/// EventWriter<'w, SomeEvent>
/// # }
/// ```
/// ## `PhantomData`
///
/// [`PhantomData`] is a special type of `SystemParam` that does nothing.
/// This is useful for constraining generic types or lifetimes.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource)]
/// # struct SomeResource;
/// use std::marker::PhantomData;
/// use bevy_ecs::system::SystemParam;
///
/// #[derive(SystemParam)]
/// struct MyParam<'w, Marker: 'static> {
/// foo: Res<'w, SomeResource>,
/// marker: PhantomData<Marker>,
/// }
///
/// fn my_system<T: 'static>(param: MyParam<T>) {
/// // Access the resource through `param.foo`
/// }
///
/// # bevy_ecs::system::assert_is_system(my_system::<()>);
/// ```
///
/// # Generic `SystemParam`s
///
/// When using the derive macro, you may see an error in the form of:
///
/// ```text
/// expected ... [ParamType]
/// found associated type `<[ParamType] as SystemParam>::Item<'_, '_>`
/// ```
/// where `[ParamType]` is the type of one of your fields.
/// To solve this error, you can wrap the field of type `[ParamType]` with [`StaticSystemParam`]
/// (i.e. `StaticSystemParam<[ParamType]>`).
///
/// ## Details
///
/// The derive macro requires that the [`SystemParam`] implementation of
/// each field `F`'s [`Item`](`SystemParam::Item`)'s is itself `F`
/// (ignoring lifetimes for simplicity).
/// This assumption is due to type inference reasons, so that the derived [`SystemParam`] can be
/// used as an argument to a function system.
/// If the compiler cannot validate this property for `[ParamType]`, it will error in the form shown above.
///
/// This will most commonly occur when working with `SystemParam`s generically, as the requirement
/// has not been proven to the compiler.
///
/// ## Builders
///
/// If you want to use a [`SystemParamBuilder`](crate::system::SystemParamBuilder) with a derived [`SystemParam`] implementation,
/// add a `#[system_param(builder)]` attribute to the struct.
/// This will generate a builder struct whose name is the param struct suffixed with `Builder`.
/// The builder will not be `pub`, so you may want to expose a method that returns an `impl SystemParamBuilder<T>`.
///
/// ```
/// mod custom_param {
/// # use bevy_ecs::{
/// # prelude::*,
/// # system::{LocalBuilder, QueryParamBuilder, SystemParam},
/// # };
/// #
/// #[derive(SystemParam)]
/// #[system_param(builder)]
/// pub struct CustomParam<'w, 's> {
/// query: Query<'w, 's, ()>,
/// local: Local<'s, usize>,
/// }
///
/// impl<'w, 's> CustomParam<'w, 's> {
/// pub fn builder(
/// local: usize,
/// query: impl FnOnce(&mut QueryBuilder<()>),
/// ) -> impl SystemParamBuilder<Self> {
/// CustomParamBuilder {
/// local: LocalBuilder(local),
/// query: QueryParamBuilder::new(query),
/// }
/// }
/// }
/// }
///
/// use custom_param::CustomParam;
///
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct A;
/// #
/// # let mut world = World::new();
/// #
/// let system = (CustomParam::builder(100, |builder| {
/// builder.with::<A>();
/// }),)
/// .build_state(&mut world)
/// .build_system(|param: CustomParam| {});
/// ```
///
/// # Safety
///
/// The implementor must ensure the following is true.
/// - [`SystemParam::init_state`] correctly registers all [`World`] accesses used
/// by [`SystemParam::get_param`] with the provided [`system_meta`](SystemMeta).
/// - None of the world accesses may conflict with any prior accesses registered
/// on `system_meta`.
pub unsafe trait SystemParam: Sized {
/// Used to store data which persists across invocations of a system.
type State: Send + Sync + 'static;
/// The item type returned when constructing this system param.
/// The value of this associated type should be `Self`, instantiated with new lifetimes.
///
/// You could think of [`SystemParam::Item<'w, 's>`] as being an *operation* that changes the lifetimes bound to `Self`.
type Item<'world, 'state>: SystemParam<State = Self::State>;
/// Registers any [`World`] access used by this [`SystemParam`]
/// and creates a new instance of this param's [`State`](SystemParam::State).
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State;
/// For the specified [`Archetype`], registers the components accessed by this [`SystemParam`] (if applicable).a
///
/// # Safety
/// `archetype` must be from the [`World`] used to initialize `state` in [`SystemParam::init_state`].
#[inline]
#[expect(
unused_variables,
reason = "The parameters here are intentionally unused by the default implementation; however, putting underscores here will result in the underscores being copied by rust-analyzer's tab completion."
)]
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
}
/// Applies any deferred mutations stored in this [`SystemParam`]'s state.
/// This is used to apply [`Commands`] during [`ApplyDeferred`](crate::prelude::ApplyDeferred).
///
/// [`Commands`]: crate::prelude::Commands
#[inline]
#[expect(
unused_variables,
reason = "The parameters here are intentionally unused by the default implementation; however, putting underscores here will result in the underscores being copied by rust-analyzer's tab completion."
)]
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World) {}
/// Queues any deferred mutations to be applied at the next [`ApplyDeferred`](crate::prelude::ApplyDeferred).
#[inline]
#[expect(
unused_variables,
reason = "The parameters here are intentionally unused by the default implementation; however, putting underscores here will result in the underscores being copied by rust-analyzer's tab completion."
)]
fn queue(state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld) {}
/// Validates that the param can be acquired by the [`get_param`](SystemParam::get_param).
/// Built-in executors use this to prevent systems with invalid params from running.
/// For nested [`SystemParam`]s validation will fail if any
/// delegated validation fails.
///
/// However calling and respecting [`SystemParam::validate_param`]
/// is not a strict requirement, [`SystemParam::get_param`] should
/// provide it's own safety mechanism to prevent undefined behavior.
///
/// The [`world`](UnsafeWorldCell) can only be used to read param's data
/// and world metadata. No data can be written.
///
/// When using system parameters that require `change_tick` you can use
/// [`UnsafeWorldCell::change_tick()`]. Even if this isn't the exact
/// same tick used for [`SystemParam::get_param`], the world access
/// ensures that the queried data will be the same in both calls.
///
/// This method has to be called directly before [`SystemParam::get_param`] with no other (relevant)
/// world mutations inbetween. Otherwise, while it won't lead to any undefined behavior,
/// the validity of the param may change.
///
/// # Safety
///
/// - The passed [`UnsafeWorldCell`] must have read-only access to world data
/// registered in [`init_state`](SystemParam::init_state).
/// - `world` must be the same [`World`] that was used to initialize [`state`](SystemParam::init_state).
/// - All `world`'s archetypes have been processed by [`new_archetype`](SystemParam::new_archetype).
#[expect(
unused_variables,
reason = "The parameters here are intentionally unused by the default implementation; however, putting underscores here will result in the underscores being copied by rust-analyzer's tab completion."
)]
unsafe fn validate_param(
state: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
// By default we allow panics in [`SystemParam::get_param`] and return `true`.
// Preventing panics is an optional feature.
true
}
/// Creates a parameter to be passed into a [`SystemParamFunction`](super::SystemParamFunction).
///
/// # Safety
///
/// - The passed [`UnsafeWorldCell`] must have access to any world data
/// registered in [`init_state`](SystemParam::init_state).
/// - `world` must be the same [`World`] that was used to initialize [`state`](SystemParam::init_state).
/// - all `world`'s archetypes have been processed by [`new_archetype`](SystemParam::new_archetype).
unsafe fn get_param<'world, 'state>(
state: &'state mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'world>,
change_tick: Tick,
) -> Self::Item<'world, 'state>;
}
/// A [`SystemParam`] that only reads a given [`World`].
///
/// # Safety
/// This must only be implemented for [`SystemParam`] impls that exclusively read the World passed in to [`SystemParam::get_param`]
pub unsafe trait ReadOnlySystemParam: SystemParam {}
/// Shorthand way of accessing the associated type [`SystemParam::Item`] for a given [`SystemParam`].
pub type SystemParamItem<'w, 's, P> = <P as SystemParam>::Item<'w, 's>;
// SAFETY: QueryState is constrained to read-only fetches, so it only reads World.
unsafe impl<'w, 's, D: ReadOnlyQueryData + 'static, F: QueryFilter + 'static> ReadOnlySystemParam
for Query<'w, 's, D, F>
{
}
// SAFETY: Relevant query ComponentId and ArchetypeComponentId access is applied to SystemMeta. If
// this Query conflicts with any prior access, a panic will occur.
unsafe impl<D: QueryData + 'static, F: QueryFilter + 'static> SystemParam for Query<'_, '_, D, F> {
type State = QueryState<D, F>;
type Item<'w, 's> = Query<'w, 's, D, F>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
let state = QueryState::new_with_access(world, &mut system_meta.archetype_component_access);
init_query_param(world, system_meta, &state);
state
}
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
state.new_archetype(archetype, &mut system_meta.archetype_component_access);
}
#[inline]
unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
// SAFETY: We have registered all of the query's world accesses,
// so the caller ensures that `world` has permission to access any
// world data that the query needs.
unsafe { state.query_unchecked_manual_with_ticks(world, system_meta.last_run, change_tick) }
}
}
pub(crate) fn init_query_param<D: QueryData + 'static, F: QueryFilter + 'static>(
world: &mut World,
system_meta: &mut SystemMeta,
state: &QueryState<D, F>,
) {
assert_component_access_compatibility(
&system_meta.name,
core::any::type_name::<D>(),
core::any::type_name::<F>(),
&system_meta.component_access_set,
&state.component_access,
world,
);
system_meta
.component_access_set
.add(state.component_access.clone());
}
fn assert_component_access_compatibility(
system_name: &str,
query_type: &'static str,
filter_type: &'static str,
system_access: &FilteredAccessSet<ComponentId>,
current: &FilteredAccess<ComponentId>,
world: &World,
) {
let conflicts = system_access.get_conflicts_single(current);
if conflicts.is_empty() {
return;
}
let mut accesses = conflicts.format_conflict_list(world);
// Access list may be empty (if access to all components requested)
if !accesses.is_empty() {
accesses.push(' ');
}
panic!("error[B0001]: Query<{}, {}> in system {system_name} accesses component(s) {accesses}in a way that conflicts with a previous system parameter. Consider using `Without<T>` to create disjoint Queries or merging conflicting Queries into a `ParamSet`. See: https://bevyengine.org/learn/errors/b0001", ShortName(query_type), ShortName(filter_type));
}
// SAFETY: Relevant query ComponentId and ArchetypeComponentId access is applied to SystemMeta. If
// this Query conflicts with any prior access, a panic will occur.
unsafe impl<'a, D: QueryData + 'static, F: QueryFilter + 'static> SystemParam for Single<'a, D, F> {
type State = QueryState<D, F>;
type Item<'w, 's> = Single<'w, D, F>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
Query::init_state(world, system_meta)
}
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
// SAFETY: Delegate to existing `SystemParam` implementations.
unsafe { Query::new_archetype(state, archetype, system_meta) };
}
#[inline]
unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
state.validate_world(world.id());
// SAFETY: State ensures that the components it accesses are not accessible somewhere elsewhere.
let query = unsafe {
state.query_unchecked_manual_with_ticks(world, system_meta.last_run, change_tick)
};
let single = query
.get_single_inner()
.expect("The query was expected to contain exactly one matching entity.");
Single {
item: single,
_filter: PhantomData,
}
}
#[inline]
unsafe fn validate_param(
state: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
state.validate_world(world.id());
// SAFETY: State ensures that the components it accesses are not mutably accessible elsewhere
// and the query is read only.
let query = unsafe {
state.query_unchecked_manual_with_ticks(
world,
system_meta.last_run,
world.change_tick(),
)
};
let is_valid = query.get_single_inner().is_ok();
if !is_valid {
system_meta.try_warn_param::<Self>();
}
is_valid
}
}
// SAFETY: Relevant query ComponentId and ArchetypeComponentId access is applied to SystemMeta. If
// this Query conflicts with any prior access, a panic will occur.
unsafe impl<'a, D: QueryData + 'static, F: QueryFilter + 'static> SystemParam
for Option<Single<'a, D, F>>
{
type State = QueryState<D, F>;
type Item<'w, 's> = Option<Single<'w, D, F>>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
Single::init_state(world, system_meta)
}
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
// SAFETY: Delegate to existing `SystemParam` implementations.
unsafe { Single::new_archetype(state, archetype, system_meta) };
}
#[inline]
unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
state.validate_world(world.id());
// SAFETY: State ensures that the components it accesses are not accessible elsewhere.
let query = unsafe {
state.query_unchecked_manual_with_ticks(world, system_meta.last_run, change_tick)
};
match query.get_single_inner() {
Ok(single) => Some(Single {
item: single,
_filter: PhantomData,
}),
Err(QuerySingleError::NoEntities(_)) => None,
Err(QuerySingleError::MultipleEntities(e)) => panic!("{}", e),
}
}
#[inline]
unsafe fn validate_param(
state: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
state.validate_world(world.id());
// SAFETY: State ensures that the components it accesses are not mutably accessible elsewhere
// and the query is read only.
let query = unsafe {
state.query_unchecked_manual_with_ticks(
world,
system_meta.last_run,
world.change_tick(),
)
};
let result = query.get_single_inner();
let is_valid = !matches!(result, Err(QuerySingleError::MultipleEntities(_)));
if !is_valid {
system_meta.try_warn_param::<Self>();
}
is_valid
}
}
// SAFETY: QueryState is constrained to read-only fetches, so it only reads World.
unsafe impl<'a, D: ReadOnlyQueryData + 'static, F: QueryFilter + 'static> ReadOnlySystemParam
for Single<'a, D, F>
{
}
// SAFETY: QueryState is constrained to read-only fetches, so it only reads World.
unsafe impl<'a, D: ReadOnlyQueryData + 'static, F: QueryFilter + 'static> ReadOnlySystemParam
for Option<Single<'a, D, F>>
{
}
// SAFETY: Relevant query ComponentId and ArchetypeComponentId access is applied to SystemMeta. If
// this Query conflicts with any prior access, a panic will occur.
unsafe impl<D: QueryData + 'static, F: QueryFilter + 'static> SystemParam
for Populated<'_, '_, D, F>
{
type State = QueryState<D, F>;
type Item<'w, 's> = Populated<'w, 's, D, F>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
Query::init_state(world, system_meta)
}
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
// SAFETY: Delegate to existing `SystemParam` implementations.
unsafe { Query::new_archetype(state, archetype, system_meta) };
}
#[inline]
unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
// SAFETY: Delegate to existing `SystemParam` implementations.
let query = unsafe { Query::get_param(state, system_meta, world, change_tick) };
Populated(query)
}
#[inline]
unsafe fn validate_param(
state: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
state.validate_world(world.id());
// SAFETY:
// - We have read-only access to the components accessed by query.
// - The world has been validated.
!unsafe {
state.is_empty_unsafe_world_cell(world, system_meta.last_run, world.change_tick())
}
}
}
// SAFETY: QueryState is constrained to read-only fetches, so it only reads World.
unsafe impl<'w, 's, D: ReadOnlyQueryData + 'static, F: QueryFilter + 'static> ReadOnlySystemParam
for Populated<'w, 's, D, F>
{
}
/// A collection of potentially conflicting [`SystemParam`]s allowed by disjoint access.
///
/// Allows systems to safely access and interact with up to 8 mutually exclusive [`SystemParam`]s, such as
/// two queries that reference the same mutable data or an event reader and writer of the same type.
///
/// Each individual [`SystemParam`] can be accessed by using the functions `p0()`, `p1()`, ..., `p7()`,
/// according to the order they are defined in the `ParamSet`. This ensures that there's either
/// only one mutable reference to a parameter at a time or any number of immutable references.
///
/// # Examples
///
/// The following system mutably accesses the same component two times,
/// which is not allowed due to rust's mutability rules.
///
/// ```should_panic
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Component)]
/// # struct Health;
/// #
/// # #[derive(Component)]
/// # struct Enemy;
/// #
/// # #[derive(Component)]
/// # struct Ally;
/// #
/// // This will panic at runtime when the system gets initialized.
/// fn bad_system(
/// mut enemies: Query<&mut Health, With<Enemy>>,
/// mut allies: Query<&mut Health, With<Ally>>,
/// ) {
/// // ...
/// }
/// #
/// # let mut bad_system_system = IntoSystem::into_system(bad_system);
/// # let mut world = World::new();
/// # bad_system_system.initialize(&mut world);
/// # bad_system_system.run((), &mut world);
/// ```
///
/// Conflicting `SystemParam`s like these can be placed in a `ParamSet`,
/// which leverages the borrow checker to ensure that only one of the contained parameters are accessed at a given time.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Component)]
/// # struct Health;
/// #
/// # #[derive(Component)]
/// # struct Enemy;
/// #
/// # #[derive(Component)]
/// # struct Ally;
/// #
/// // Given the following system
/// fn fancy_system(
/// mut set: ParamSet<(
/// Query<&mut Health, With<Enemy>>,
/// Query<&mut Health, With<Ally>>,
/// )>
/// ) {
/// // This will access the first `SystemParam`.
/// for mut health in set.p0().iter_mut() {
/// // Do your fancy stuff here...
/// }
///
/// // The second `SystemParam`.
/// // This would fail to compile if the previous parameter was still borrowed.
/// for mut health in set.p1().iter_mut() {
/// // Do even fancier stuff here...
/// }
/// }
/// # bevy_ecs::system::assert_is_system(fancy_system);
/// ```
///
/// Of course, `ParamSet`s can be used with any kind of `SystemParam`, not just [queries](Query).
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Event)]
/// # struct MyEvent;
/// # impl MyEvent {
/// # pub fn new() -> Self { Self }
/// # }
/// fn event_system(
/// mut set: ParamSet<(
/// // PROBLEM: `EventReader` and `EventWriter` cannot be used together normally,
/// // because they both need access to the same event queue.
/// // SOLUTION: `ParamSet` allows these conflicting parameters to be used safely
/// // by ensuring only one is accessed at a time.
/// EventReader<MyEvent>,
/// EventWriter<MyEvent>,
/// // PROBLEM: `&World` needs read access to everything, which conflicts with
/// // any mutable access in the same system.
/// // SOLUTION: `ParamSet` ensures `&World` is only accessed when we're not
/// // using the other mutable parameters.
/// &World,
/// )>,
/// ) {
/// for event in set.p0().read() {
/// // ...
/// # let _event = event;
/// }
/// set.p1().send(MyEvent::new());
///
/// let entities = set.p2().entities();
/// // ...
/// # let _entities = entities;
/// }
/// # bevy_ecs::system::assert_is_system(event_system);
/// ```
pub struct ParamSet<'w, 's, T: SystemParam> {
param_states: &'s mut T::State,
world: UnsafeWorldCell<'w>,
system_meta: SystemMeta,
change_tick: Tick,
}
macro_rules! impl_param_set {
($(($index: tt, $param: ident, $system_meta: ident, $fn_name: ident)),*) => {
// SAFETY: All parameters are constrained to ReadOnlySystemParam, so World is only read
unsafe impl<'w, 's, $($param,)*> ReadOnlySystemParam for ParamSet<'w, 's, ($($param,)*)>
where $($param: ReadOnlySystemParam,)*
{ }
// SAFETY: Relevant parameter ComponentId and ArchetypeComponentId access is applied to SystemMeta. If any ParamState conflicts
// with any prior access, a panic will occur.
unsafe impl<'_w, '_s, $($param: SystemParam,)*> SystemParam for ParamSet<'_w, '_s, ($($param,)*)>
{
type State = ($($param::State,)*);
type Item<'w, 's> = ParamSet<'w, 's, ($($param,)*)>;
#[expect(
clippy::allow_attributes,
reason = "This is inside a macro meant for tuples; as such, `non_snake_case` won't always lint."
)]
#[allow(
non_snake_case,
reason = "Certain variable names are provided by the caller, not by us."
)]
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
$(
// Pretend to add each param to the system alone, see if it conflicts
let mut $system_meta = system_meta.clone();
$system_meta.component_access_set.clear();
$system_meta.archetype_component_access.clear();
$param::init_state(world, &mut $system_meta);
// The variable is being defined with non_snake_case here
let $param = $param::init_state(world, &mut system_meta.clone());
)*
// Make the ParamSet non-send if any of its parameters are non-send.
if false $(|| !$system_meta.is_send())* {
system_meta.set_non_send();
}
$(
system_meta
.component_access_set
.extend($system_meta.component_access_set);
system_meta
.archetype_component_access
.extend(&$system_meta.archetype_component_access);
)*
($($param,)*)
}
unsafe fn new_archetype(state: &mut Self::State, archetype: &Archetype, system_meta: &mut SystemMeta) {
// SAFETY: The caller ensures that `archetype` is from the World the state was initialized from in `init_state`.
unsafe { <($($param,)*) as SystemParam>::new_archetype(state, archetype, system_meta); }
}
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World) {
<($($param,)*) as SystemParam>::apply(state, system_meta, world);
}
fn queue(state: &mut Self::State, system_meta: &SystemMeta, mut world: DeferredWorld) {
<($($param,)*) as SystemParam>::queue(state, system_meta, world.reborrow());
}
#[inline]
unsafe fn validate_param<'w, 's>(
state: &'s Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
) -> bool {
<($($param,)*) as SystemParam>::validate_param(state, system_meta, world)
}
#[inline]
unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
ParamSet {
param_states: state,
system_meta: system_meta.clone(),
world,
change_tick,
}
}
}
impl<'w, 's, $($param: SystemParam,)*> ParamSet<'w, 's, ($($param,)*)>
{
$(
/// Gets exclusive access to the parameter at index
#[doc = stringify!($index)]
/// in this [`ParamSet`].
/// No other parameters may be accessed while this one is active.
pub fn $fn_name<'a>(&'a mut self) -> SystemParamItem<'a, 'a, $param> {
// SAFETY: systems run without conflicts with other systems.
// Conflicting params in ParamSet are not accessible at the same time
// ParamSets are guaranteed to not conflict with other SystemParams
unsafe {
$param::get_param(&mut self.param_states.$index, &self.system_meta, self.world, self.change_tick)
}
}
)*
}
}
}
all_tuples_enumerated!(impl_param_set, 1, 8, P, m, p);
// SAFETY: Res only reads a single World resource
unsafe impl<'a, T: Resource> ReadOnlySystemParam for Res<'a, T> {}
// SAFETY: Res ComponentId and ArchetypeComponentId access is applied to SystemMeta. If this Res
// conflicts with any prior access, a panic will occur.
unsafe impl<'a, T: Resource> SystemParam for Res<'a, T> {
type State = ComponentId;
type Item<'w, 's> = Res<'w, T>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
let component_id = world.components.register_resource::<T>();
let archetype_component_id = world.initialize_resource_internal(component_id).id();
let combined_access = system_meta.component_access_set.combined_access();
assert!(
!combined_access.has_resource_write(component_id),
"error[B0002]: Res<{}> in system {} conflicts with a previous ResMut<{0}> access. Consider removing the duplicate access. See: https://bevyengine.org/learn/errors/b0002",
core::any::type_name::<T>(),
system_meta.name,
);
system_meta
.component_access_set
.add_unfiltered_resource_read(component_id);
system_meta
.archetype_component_access
.add_resource_read(archetype_component_id);
component_id
}
#[inline]
unsafe fn validate_param(
&component_id: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
// SAFETY: Read-only access to resource metadata.
let is_valid = unsafe { world.storages() }
.resources
.get(component_id)
.is_some_and(ResourceData::is_present);
if !is_valid {
system_meta.try_warn_param::<Self>();
}
is_valid
}
#[inline]
unsafe fn get_param<'w, 's>(
&mut component_id: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
let (ptr, ticks, caller) =
world
.get_resource_with_ticks(component_id)
.unwrap_or_else(|| {
panic!(
"Resource requested by {} does not exist: {}",
system_meta.name,
core::any::type_name::<T>()
)
});
Res {
value: ptr.deref(),
ticks: Ticks {
added: ticks.added.deref(),
changed: ticks.changed.deref(),
last_run: system_meta.last_run,
this_run: change_tick,
},
changed_by: caller.map(|caller| caller.deref()),
}
}
}
// SAFETY: Only reads a single World resource
unsafe impl<'a, T: Resource> ReadOnlySystemParam for Option<Res<'a, T>> {}
// SAFETY: this impl defers to `Res`, which initializes and validates the correct world access.
unsafe impl<'a, T: Resource> SystemParam for Option<Res<'a, T>> {
type State = ComponentId;
type Item<'w, 's> = Option<Res<'w, T>>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
Res::<T>::init_state(world, system_meta)
}
#[inline]
unsafe fn get_param<'w, 's>(
&mut component_id: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
world
.get_resource_with_ticks(component_id)
.map(|(ptr, ticks, caller)| Res {
value: ptr.deref(),
ticks: Ticks {
added: ticks.added.deref(),
changed: ticks.changed.deref(),
last_run: system_meta.last_run,
this_run: change_tick,
},
changed_by: caller.map(|caller| caller.deref()),
})
}
}
// SAFETY: Res ComponentId and ArchetypeComponentId access is applied to SystemMeta. If this Res
// conflicts with any prior access, a panic will occur.
unsafe impl<'a, T: Resource> SystemParam for ResMut<'a, T> {
type State = ComponentId;
type Item<'w, 's> = ResMut<'w, T>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
let component_id = world.components.register_resource::<T>();
let archetype_component_id = world.initialize_resource_internal(component_id).id();
let combined_access = system_meta.component_access_set.combined_access();
if combined_access.has_resource_write(component_id) {
panic!(
"error[B0002]: ResMut<{}> in system {} conflicts with a previous ResMut<{0}> access. Consider removing the duplicate access. See: https://bevyengine.org/learn/errors/b0002",
core::any::type_name::<T>(), system_meta.name);
} else if combined_access.has_resource_read(component_id) {
panic!(
"error[B0002]: ResMut<{}> in system {} conflicts with a previous Res<{0}> access. Consider removing the duplicate access. See: https://bevyengine.org/learn/errors/b0002",
core::any::type_name::<T>(), system_meta.name);
}
system_meta
.component_access_set
.add_unfiltered_resource_write(component_id);
system_meta
.archetype_component_access
.add_resource_write(archetype_component_id);
component_id
}
#[inline]
unsafe fn validate_param(
&component_id: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
// SAFETY: Read-only access to resource metadata.
let is_valid = unsafe { world.storages() }
.resources
.get(component_id)
.is_some_and(ResourceData::is_present);
if !is_valid {
system_meta.try_warn_param::<Self>();
}
is_valid
}
#[inline]
unsafe fn get_param<'w, 's>(
&mut component_id: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
let value = world
.get_resource_mut_by_id(component_id)
.unwrap_or_else(|| {
panic!(
"Resource requested by {} does not exist: {}",
system_meta.name,
core::any::type_name::<T>()
)
});
ResMut {
value: value.value.deref_mut::<T>(),
ticks: TicksMut {
added: value.ticks.added,
changed: value.ticks.changed,
last_run: system_meta.last_run,
this_run: change_tick,
},
changed_by: value.changed_by,
}
}
}
// SAFETY: this impl defers to `ResMut`, which initializes and validates the correct world access.
unsafe impl<'a, T: Resource> SystemParam for Option<ResMut<'a, T>> {
type State = ComponentId;
type Item<'w, 's> = Option<ResMut<'w, T>>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
ResMut::<T>::init_state(world, system_meta)
}
#[inline]
unsafe fn get_param<'w, 's>(
&mut component_id: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
world
.get_resource_mut_by_id(component_id)
.map(|value| ResMut {
value: value.value.deref_mut::<T>(),
ticks: TicksMut {
added: value.ticks.added,
changed: value.ticks.changed,
last_run: system_meta.last_run,
this_run: change_tick,
},
changed_by: value.changed_by,
})
}
}
/// SAFETY: only reads world
unsafe impl<'w> ReadOnlySystemParam for &'w World {}
// SAFETY: `read_all` access is set and conflicts result in a panic
unsafe impl SystemParam for &'_ World {
type State = ();
type Item<'w, 's> = &'w World;
fn init_state(_world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
let mut access = Access::default();
access.read_all();
if !system_meta
.archetype_component_access
.is_compatible(&access)
{
panic!("&World conflicts with a previous mutable system parameter. Allowing this would break Rust's mutability rules");
}
system_meta.archetype_component_access.extend(&access);
let mut filtered_access = FilteredAccess::default();
filtered_access.read_all();
if !system_meta
.component_access_set
.get_conflicts_single(&filtered_access)
.is_empty()
{
panic!("&World conflicts with a previous mutable system parameter. Allowing this would break Rust's mutability rules");
}
system_meta.component_access_set.add(filtered_access);
}
#[inline]
unsafe fn get_param<'w, 's>(
_state: &'s mut Self::State,
_system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
_change_tick: Tick,
) -> Self::Item<'w, 's> {
// SAFETY: Read-only access to the entire world was registered in `init_state`.
unsafe { world.world() }
}
}
/// SAFETY: `DeferredWorld` can read all components and resources but cannot be used to gain any other mutable references.
unsafe impl<'w> SystemParam for DeferredWorld<'w> {
type State = ();
type Item<'world, 'state> = DeferredWorld<'world>;
fn init_state(_world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
assert!(
!system_meta
.component_access_set
.combined_access()
.has_any_read(),
"DeferredWorld in system {} conflicts with a previous access.",
system_meta.name,
);
system_meta.component_access_set.write_all();
system_meta.archetype_component_access.write_all();
}
unsafe fn get_param<'world, 'state>(
_state: &'state mut Self::State,
_system_meta: &SystemMeta,
world: UnsafeWorldCell<'world>,
_change_tick: Tick,
) -> Self::Item<'world, 'state> {
world.into_deferred()
}
}
/// A system local [`SystemParam`].
///
/// A local may only be accessed by the system itself and is therefore not visible to other systems.
/// If two or more systems specify the same local type each will have their own unique local.
/// If multiple [`SystemParam`]s within the same system each specify the same local type
/// each will get their own distinct data storage.
///
/// The supplied lifetime parameter is the [`SystemParam`]s `'s` lifetime.
///
/// # Examples
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # let world = &mut World::default();
/// fn write_to_local(mut local: Local<usize>) {
/// *local = 42;
/// }
/// fn read_from_local(local: Local<usize>) -> usize {
/// *local
/// }
/// let mut write_system = IntoSystem::into_system(write_to_local);
/// let mut read_system = IntoSystem::into_system(read_from_local);
/// write_system.initialize(world);
/// read_system.initialize(world);
///
/// assert_eq!(read_system.run((), world), 0);
/// write_system.run((), world);
/// // Note how the read local is still 0 due to the locals not being shared.
/// assert_eq!(read_system.run((), world), 0);
/// ```
///
/// A simple way to set a different default value for a local is by wrapping the value with an Option.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # let world = &mut World::default();
/// fn counter_from_10(mut count: Local<Option<usize>>) -> usize {
/// let count = count.get_or_insert(10);
/// *count += 1;
/// *count
/// }
/// let mut counter_system = IntoSystem::into_system(counter_from_10);
/// counter_system.initialize(world);
///
/// // Counter is initialized at 10, and increases to 11 on first run.
/// assert_eq!(counter_system.run((), world), 11);
/// // Counter is only increased by 1 on subsequent runs.
/// assert_eq!(counter_system.run((), world), 12);
/// ```
///
/// N.B. A [`Local`]s value cannot be read or written to outside of the containing system.
/// To add configuration to a system, convert a capturing closure into the system instead:
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # use bevy_ecs::system::assert_is_system;
/// struct Config(u32);
/// #[derive(Resource)]
/// struct MyU32Wrapper(u32);
/// fn reset_to_system(value: Config) -> impl FnMut(ResMut<MyU32Wrapper>) {
/// move |mut val| val.0 = value.0
/// }
///
/// // .add_systems(reset_to_system(my_config))
/// # assert_is_system(reset_to_system(Config(10)));
/// ```
#[derive(Debug)]
pub struct Local<'s, T: FromWorld + Send + 'static>(pub(crate) &'s mut T);
// SAFETY: Local only accesses internal state
unsafe impl<'s, T: FromWorld + Send + 'static> ReadOnlySystemParam for Local<'s, T> {}
impl<'s, T: FromWorld + Send + 'static> Deref for Local<'s, T> {
type Target = T;
#[inline]
fn deref(&self) -> &Self::Target {
self.0
}
}
impl<'s, T: FromWorld + Send + 'static> DerefMut for Local<'s, T> {
#[inline]
fn deref_mut(&mut self) -> &mut Self::Target {
self.0
}
}
impl<'s, 'a, T: FromWorld + Send + 'static> IntoIterator for &'a Local<'s, T>
where
&'a T: IntoIterator,
{
type Item = <&'a T as IntoIterator>::Item;
type IntoIter = <&'a T as IntoIterator>::IntoIter;
fn into_iter(self) -> Self::IntoIter {
self.0.into_iter()
}
}
impl<'s, 'a, T: FromWorld + Send + 'static> IntoIterator for &'a mut Local<'s, T>
where
&'a mut T: IntoIterator,
{
type Item = <&'a mut T as IntoIterator>::Item;
type IntoIter = <&'a mut T as IntoIterator>::IntoIter;
fn into_iter(self) -> Self::IntoIter {
self.0.into_iter()
}
}
// SAFETY: only local state is accessed
unsafe impl<'a, T: FromWorld + Send + 'static> SystemParam for Local<'a, T> {
type State = SyncCell<T>;
type Item<'w, 's> = Local<'s, T>;
fn init_state(world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
SyncCell::new(T::from_world(world))
}
#[inline]
unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
_system_meta: &SystemMeta,
_world: UnsafeWorldCell<'w>,
_change_tick: Tick,
) -> Self::Item<'w, 's> {
Local(state.get())
}
}
/// Types that can be used with [`Deferred<T>`] in systems.
/// This allows storing system-local data which is used to defer [`World`] mutations.
///
/// Types that implement `SystemBuffer` should take care to perform as many
/// computations up-front as possible. Buffers cannot be applied in parallel,
/// so you should try to minimize the time spent in [`SystemBuffer::apply`].
pub trait SystemBuffer: FromWorld + Send + 'static {
/// Applies any deferred mutations to the [`World`].
fn apply(&mut self, system_meta: &SystemMeta, world: &mut World);
/// Queues any deferred mutations to be applied at the next [`ApplyDeferred`](crate::prelude::ApplyDeferred).
fn queue(&mut self, _system_meta: &SystemMeta, _world: DeferredWorld) {}
}
/// A [`SystemParam`] that stores a buffer which gets applied to the [`World`] during
/// [`ApplyDeferred`](crate::schedule::ApplyDeferred).
/// This is used internally by [`Commands`] to defer `World` mutations.
///
/// [`Commands`]: crate::system::Commands
///
/// # Examples
///
/// By using this type to defer mutations, you can avoid mutable `World` access within
/// a system, which allows it to run in parallel with more systems.
///
/// Note that deferring mutations is *not* free, and should only be used if
/// the gains in parallelization outweigh the time it takes to apply deferred mutations.
/// In general, [`Deferred`] should only be used for mutations that are infrequent,
/// or which otherwise take up a small portion of a system's run-time.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// // Tracks whether or not there is a threat the player should be aware of.
/// #[derive(Resource, Default)]
/// pub struct Alarm(bool);
///
/// #[derive(Component)]
/// pub struct Settlement {
/// // ...
/// }
///
/// // A threat from inside the settlement.
/// #[derive(Component)]
/// pub struct Criminal;
///
/// // A threat from outside the settlement.
/// #[derive(Component)]
/// pub struct Monster;
///
/// # impl Criminal { pub fn is_threat(&self, _: &Settlement) -> bool { true } }
///
/// use bevy_ecs::system::{Deferred, SystemBuffer, SystemMeta};
///
/// // Uses deferred mutations to allow signaling the alarm from multiple systems in parallel.
/// #[derive(Resource, Default)]
/// struct AlarmFlag(bool);
///
/// impl AlarmFlag {
/// /// Sounds the alarm the next time buffers are applied via ApplyDeferred.
/// pub fn flag(&mut self) {
/// self.0 = true;
/// }
/// }
///
/// impl SystemBuffer for AlarmFlag {
/// // When `AlarmFlag` is used in a system, this function will get
/// // called the next time buffers are applied via ApplyDeferred.
/// fn apply(&mut self, system_meta: &SystemMeta, world: &mut World) {
/// if self.0 {
/// world.resource_mut::<Alarm>().0 = true;
/// self.0 = false;
/// }
/// }
/// }
///
/// // Sound the alarm if there are any criminals who pose a threat.
/// fn alert_criminal(
/// settlement: Single<&Settlement>,
/// criminals: Query<&Criminal>,
/// mut alarm: Deferred<AlarmFlag>
/// ) {
/// for criminal in &criminals {
/// // Only sound the alarm if the criminal is a threat.
/// // For this example, assume that this check is expensive to run.
/// // Since the majority of this system's run-time is dominated
/// // by calling `is_threat()`, we defer sounding the alarm to
/// // allow this system to run in parallel with other alarm systems.
/// if criminal.is_threat(*settlement) {
/// alarm.flag();
/// }
/// }
/// }
///
/// // Sound the alarm if there is a monster.
/// fn alert_monster(
/// monsters: Query<&Monster>,
/// mut alarm: ResMut<Alarm>
/// ) {
/// if monsters.iter().next().is_some() {
/// // Since this system does nothing except for sounding the alarm,
/// // it would be pointless to defer it, so we sound the alarm directly.
/// alarm.0 = true;
/// }
/// }
///
/// let mut world = World::new();
/// world.init_resource::<Alarm>();
/// world.spawn(Settlement {
/// // ...
/// });
///
/// let mut schedule = Schedule::default();
/// // These two systems have no conflicts and will run in parallel.
/// schedule.add_systems((alert_criminal, alert_monster));
///
/// // There are no criminals or monsters, so the alarm is not sounded.
/// schedule.run(&mut world);
/// assert_eq!(world.resource::<Alarm>().0, false);
///
/// // Spawn a monster, which will cause the alarm to be sounded.
/// let m_id = world.spawn(Monster).id();
/// schedule.run(&mut world);
/// assert_eq!(world.resource::<Alarm>().0, true);
///
/// // Remove the monster and reset the alarm.
/// world.entity_mut(m_id).despawn();
/// world.resource_mut::<Alarm>().0 = false;
///
/// // Spawn a criminal, which will cause the alarm to be sounded.
/// world.spawn(Criminal);
/// schedule.run(&mut world);
/// assert_eq!(world.resource::<Alarm>().0, true);
/// ```
pub struct Deferred<'a, T: SystemBuffer>(pub(crate) &'a mut T);
impl<'a, T: SystemBuffer> Deref for Deferred<'a, T> {
type Target = T;
#[inline]
fn deref(&self) -> &Self::Target {
self.0
}
}
impl<'a, T: SystemBuffer> DerefMut for Deferred<'a, T> {
#[inline]
fn deref_mut(&mut self) -> &mut Self::Target {
self.0
}
}
impl<T: SystemBuffer> Deferred<'_, T> {
/// Returns a [`Deferred<T>`] with a smaller lifetime.
/// This is useful if you have `&mut Deferred<T>` but need `Deferred<T>`.
pub fn reborrow(&mut self) -> Deferred<T> {
Deferred(self.0)
}
}
// SAFETY: Only local state is accessed.
unsafe impl<T: SystemBuffer> ReadOnlySystemParam for Deferred<'_, T> {}
// SAFETY: Only local state is accessed.
unsafe impl<T: SystemBuffer> SystemParam for Deferred<'_, T> {
type State = SyncCell<T>;
type Item<'w, 's> = Deferred<'s, T>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
system_meta.set_has_deferred();
SyncCell::new(T::from_world(world))
}
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World) {
state.get().apply(system_meta, world);
}
fn queue(state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld) {
state.get().queue(system_meta, world);
}
#[inline]
unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
_system_meta: &SystemMeta,
_world: UnsafeWorldCell<'w>,
_change_tick: Tick,
) -> Self::Item<'w, 's> {
Deferred(state.get())
}
}
/// Shared borrow of a non-[`Send`] resource.
///
/// Only `Send` resources may be accessed with the [`Res`] [`SystemParam`]. In case that the
/// resource does not implement `Send`, this `SystemParam` wrapper can be used. This will instruct
/// the scheduler to instead run the system on the main thread so that it doesn't send the resource
/// over to another thread.
///
/// This [`SystemParam`] fails validation if non-send resource doesn't exist.
/// This will cause a panic, but can be configured to do nothing or warn once.
///
/// Use [`Option<NonSend<T>>`] instead if the resource might not always exist.
pub struct NonSend<'w, T: 'static> {
pub(crate) value: &'w T,
ticks: ComponentTicks,
last_run: Tick,
this_run: Tick,
changed_by: MaybeLocation<&'w &'static Location<'static>>,
}
// SAFETY: Only reads a single World non-send resource
unsafe impl<'w, T> ReadOnlySystemParam for NonSend<'w, T> {}
impl<'w, T> Debug for NonSend<'w, T>
where
T: Debug,
{
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
f.debug_tuple("NonSend").field(&self.value).finish()
}
}
impl<'w, T: 'static> NonSend<'w, T> {
/// Returns `true` if the resource was added after the system last ran.
pub fn is_added(&self) -> bool {
self.ticks.is_added(self.last_run, self.this_run)
}
/// Returns `true` if the resource was added or mutably dereferenced after the system last ran.
pub fn is_changed(&self) -> bool {
self.ticks.is_changed(self.last_run, self.this_run)
}
/// The location that last caused this to change.
pub fn changed_by(&self) -> MaybeLocation {
self.changed_by.copied()
}
}
impl<'w, T> Deref for NonSend<'w, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
self.value
}
}
impl<'a, T> From<NonSendMut<'a, T>> for NonSend<'a, T> {
fn from(nsm: NonSendMut<'a, T>) -> Self {
Self {
value: nsm.value,
ticks: ComponentTicks {
added: nsm.ticks.added.to_owned(),
changed: nsm.ticks.changed.to_owned(),
},
this_run: nsm.ticks.this_run,
last_run: nsm.ticks.last_run,
changed_by: nsm.changed_by.map(|changed_by| &*changed_by),
}
}
}
// SAFETY: NonSendComponentId and ArchetypeComponentId access is applied to SystemMeta. If this
// NonSend conflicts with any prior access, a panic will occur.
unsafe impl<'a, T: 'static> SystemParam for NonSend<'a, T> {
type State = ComponentId;
type Item<'w, 's> = NonSend<'w, T>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
system_meta.set_non_send();
let component_id = world.components.register_non_send::<T>();
let archetype_component_id = world.initialize_non_send_internal(component_id).id();
let combined_access = system_meta.component_access_set.combined_access();
assert!(
!combined_access.has_resource_write(component_id),
"error[B0002]: NonSend<{}> in system {} conflicts with a previous mutable resource access ({0}). Consider removing the duplicate access. See: https://bevyengine.org/learn/errors/b0002",
core::any::type_name::<T>(),
system_meta.name,
);
system_meta
.component_access_set
.add_unfiltered_resource_read(component_id);
system_meta
.archetype_component_access
.add_resource_read(archetype_component_id);
component_id
}
#[inline]
unsafe fn validate_param(
&component_id: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
// SAFETY: Read-only access to resource metadata.
let is_valid = unsafe { world.storages() }
.non_send_resources
.get(component_id)
.is_some_and(ResourceData::is_present);
if !is_valid {
system_meta.try_warn_param::<Self>();
}
is_valid
}
#[inline]
unsafe fn get_param<'w, 's>(
&mut component_id: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
let (ptr, ticks, caller) =
world
.get_non_send_with_ticks(component_id)
.unwrap_or_else(|| {
panic!(
"Non-send resource requested by {} does not exist: {}",
system_meta.name,
core::any::type_name::<T>()
)
});
NonSend {
value: ptr.deref(),
ticks: ticks.read(),
last_run: system_meta.last_run,
this_run: change_tick,
changed_by: caller.map(|caller| caller.deref()),
}
}
}
// SAFETY: Only reads a single World non-send resource
unsafe impl<T: 'static> ReadOnlySystemParam for Option<NonSend<'_, T>> {}
// SAFETY: this impl defers to `NonSend`, which initializes and validates the correct world access.
unsafe impl<T: 'static> SystemParam for Option<NonSend<'_, T>> {
type State = ComponentId;
type Item<'w, 's> = Option<NonSend<'w, T>>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
NonSend::<T>::init_state(world, system_meta)
}
#[inline]
unsafe fn get_param<'w, 's>(
&mut component_id: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
world
.get_non_send_with_ticks(component_id)
.map(|(ptr, ticks, caller)| NonSend {
value: ptr.deref(),
ticks: ticks.read(),
last_run: system_meta.last_run,
this_run: change_tick,
changed_by: caller.map(|caller| caller.deref()),
})
}
}
// SAFETY: NonSendMut ComponentId and ArchetypeComponentId access is applied to SystemMeta. If this
// NonSendMut conflicts with any prior access, a panic will occur.
unsafe impl<'a, T: 'static> SystemParam for NonSendMut<'a, T> {
type State = ComponentId;
type Item<'w, 's> = NonSendMut<'w, T>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
system_meta.set_non_send();
let component_id = world.components.register_non_send::<T>();
let archetype_component_id = world.initialize_non_send_internal(component_id).id();
let combined_access = system_meta.component_access_set.combined_access();
if combined_access.has_component_write(component_id) {
panic!(
"error[B0002]: NonSendMut<{}> in system {} conflicts with a previous mutable resource access ({0}). Consider removing the duplicate access. See: https://bevyengine.org/learn/errors/b0002",
core::any::type_name::<T>(), system_meta.name);
} else if combined_access.has_component_read(component_id) {
panic!(
"error[B0002]: NonSendMut<{}> in system {} conflicts with a previous immutable resource access ({0}). Consider removing the duplicate access. See: https://bevyengine.org/learn/errors/b0002",
core::any::type_name::<T>(), system_meta.name);
}
system_meta
.component_access_set
.add_unfiltered_resource_write(component_id);
system_meta
.archetype_component_access
.add_resource_write(archetype_component_id);
component_id
}
#[inline]
unsafe fn validate_param(
&component_id: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
// SAFETY: Read-only access to resource metadata.
let is_valid = unsafe { world.storages() }
.non_send_resources
.get(component_id)
.is_some_and(ResourceData::is_present);
if !is_valid {
system_meta.try_warn_param::<Self>();
}
is_valid
}
#[inline]
unsafe fn get_param<'w, 's>(
&mut component_id: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
let (ptr, ticks, caller) =
world
.get_non_send_with_ticks(component_id)
.unwrap_or_else(|| {
panic!(
"Non-send resource requested by {} does not exist: {}",
system_meta.name,
core::any::type_name::<T>()
)
});
NonSendMut {
value: ptr.assert_unique().deref_mut(),
ticks: TicksMut::from_tick_cells(ticks, system_meta.last_run, change_tick),
changed_by: caller.map(|caller| caller.deref_mut()),
}
}
}
// SAFETY: this impl defers to `NonSendMut`, which initializes and validates the correct world access.
unsafe impl<'a, T: 'static> SystemParam for Option<NonSendMut<'a, T>> {
type State = ComponentId;
type Item<'w, 's> = Option<NonSendMut<'w, T>>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
NonSendMut::<T>::init_state(world, system_meta)
}
#[inline]
unsafe fn get_param<'w, 's>(
&mut component_id: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
world
.get_non_send_with_ticks(component_id)
.map(|(ptr, ticks, caller)| NonSendMut {
value: ptr.assert_unique().deref_mut(),
ticks: TicksMut::from_tick_cells(ticks, system_meta.last_run, change_tick),
changed_by: caller.map(|caller| caller.deref_mut()),
})
}
}
// SAFETY: Only reads World archetypes
unsafe impl<'a> ReadOnlySystemParam for &'a Archetypes {}
// SAFETY: no component value access
unsafe impl<'a> SystemParam for &'a Archetypes {
type State = ();
type Item<'w, 's> = &'w Archetypes;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
#[inline]
unsafe fn get_param<'w, 's>(
_state: &'s mut Self::State,
_system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
_change_tick: Tick,
) -> Self::Item<'w, 's> {
world.archetypes()
}
}
// SAFETY: Only reads World components
unsafe impl<'a> ReadOnlySystemParam for &'a Components {}
// SAFETY: no component value access
unsafe impl<'a> SystemParam for &'a Components {
type State = ();
type Item<'w, 's> = &'w Components;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
#[inline]
unsafe fn get_param<'w, 's>(
_state: &'s mut Self::State,
_system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
_change_tick: Tick,
) -> Self::Item<'w, 's> {
world.components()
}
}
// SAFETY: Only reads World entities
unsafe impl<'a> ReadOnlySystemParam for &'a Entities {}
// SAFETY: no component value access
unsafe impl<'a> SystemParam for &'a Entities {
type State = ();
type Item<'w, 's> = &'w Entities;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
#[inline]
unsafe fn get_param<'w, 's>(
_state: &'s mut Self::State,
_system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
_change_tick: Tick,
) -> Self::Item<'w, 's> {
world.entities()
}
}
// SAFETY: Only reads World bundles
unsafe impl<'a> ReadOnlySystemParam for &'a Bundles {}
// SAFETY: no component value access
unsafe impl<'a> SystemParam for &'a Bundles {
type State = ();
type Item<'w, 's> = &'w Bundles;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
#[inline]
unsafe fn get_param<'w, 's>(
_state: &'s mut Self::State,
_system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
_change_tick: Tick,
) -> Self::Item<'w, 's> {
world.bundles()
}
}
/// A [`SystemParam`] that reads the previous and current change ticks of the system.
///
/// A system's change ticks are updated each time it runs:
/// - `last_run` copies the previous value of `change_tick`
/// - `this_run` copies the current value of [`World::read_change_tick`]
///
/// Component change ticks that are more recent than `last_run` will be detected by the system.
/// Those can be read by calling [`last_changed`](crate::change_detection::DetectChanges::last_changed)
/// on a [`Mut<T>`](crate::change_detection::Mut) or [`ResMut<T>`](ResMut).
#[derive(Debug)]
pub struct SystemChangeTick {
last_run: Tick,
this_run: Tick,
}
impl SystemChangeTick {
/// Returns the current [`World`] change tick seen by the system.
#[inline]
pub fn this_run(&self) -> Tick {
self.this_run
}
/// Returns the [`World`] change tick seen by the system the previous time it ran.
#[inline]
pub fn last_run(&self) -> Tick {
self.last_run
}
}
// SAFETY: Only reads internal system state
unsafe impl ReadOnlySystemParam for SystemChangeTick {}
// SAFETY: `SystemChangeTick` doesn't require any world access
unsafe impl SystemParam for SystemChangeTick {
type State = ();
type Item<'w, 's> = SystemChangeTick;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
#[inline]
unsafe fn get_param<'w, 's>(
_state: &'s mut Self::State,
system_meta: &SystemMeta,
_world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
SystemChangeTick {
last_run: system_meta.last_run,
this_run: change_tick,
}
}
}
// SAFETY: When initialized with `init_state`, `get_param` returns an empty `Vec` and does no access.
// Therefore, `init_state` trivially registers all access, and no accesses can conflict.
// Note that the safety requirements for non-empty `Vec`s are handled by the `SystemParamBuilder` impl that builds them.
unsafe impl<T: SystemParam> SystemParam for Vec<T> {
type State = Vec<T::State>;
type Item<'world, 'state> = Vec<T::Item<'world, 'state>>;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
Vec::new()
}
#[inline]
unsafe fn validate_param(
state: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
state
.iter()
.all(|state| T::validate_param(state, system_meta, world))
}
#[inline]
unsafe fn get_param<'world, 'state>(
state: &'state mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'world>,
change_tick: Tick,
) -> Self::Item<'world, 'state> {
state
.iter_mut()
// SAFETY:
// - We initialized the state for each parameter in the builder, so the caller ensures we have access to any world data needed by each param.
// - The caller ensures this was the world used to initialize our state, and we used that world to initialize parameter states
.map(|state| unsafe { T::get_param(state, system_meta, world, change_tick) })
.collect()
}
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
for state in state {
// SAFETY: The caller ensures that `archetype` is from the World the state was initialized from in `init_state`.
unsafe { T::new_archetype(state, archetype, system_meta) };
}
}
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World) {
for state in state {
T::apply(state, system_meta, world);
}
}
fn queue(state: &mut Self::State, system_meta: &SystemMeta, mut world: DeferredWorld) {
for state in state {
T::queue(state, system_meta, world.reborrow());
}
}
}
// SAFETY: When initialized with `init_state`, `get_param` returns an empty `Vec` and does no access.
// Therefore, `init_state` trivially registers all access, and no accesses can conflict.
// Note that the safety requirements for non-empty `Vec`s are handled by the `SystemParamBuilder` impl that builds them.
unsafe impl<T: SystemParam> SystemParam for ParamSet<'_, '_, Vec<T>> {
type State = Vec<T::State>;
type Item<'world, 'state> = ParamSet<'world, 'state, Vec<T>>;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
Vec::new()
}
#[inline]
unsafe fn get_param<'world, 'state>(
state: &'state mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'world>,
change_tick: Tick,
) -> Self::Item<'world, 'state> {
ParamSet {
param_states: state,
system_meta: system_meta.clone(),
world,
change_tick,
}
}
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
for state in state {
// SAFETY: The caller ensures that `archetype` is from the World the state was initialized from in `init_state`.
unsafe { T::new_archetype(state, archetype, system_meta) }
}
}
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World) {
for state in state {
T::apply(state, system_meta, world);
}
}
fn queue(state: &mut Self::State, system_meta: &SystemMeta, mut world: DeferredWorld) {
for state in state {
T::queue(state, system_meta, world.reborrow());
}
}
}
impl<T: SystemParam> ParamSet<'_, '_, Vec<T>> {
/// Accesses the parameter at the given index.
/// No other parameters may be accessed while this one is active.
pub fn get_mut(&mut self, index: usize) -> T::Item<'_, '_> {
// SAFETY:
// - We initialized the state for each parameter in the builder, so the caller ensures we have access to any world data needed by any param.
// We have mutable access to the ParamSet, so no other params in the set are active.
// - The caller of `get_param` ensured that this was the world used to initialize our state, and we used that world to initialize parameter states
unsafe {
T::get_param(
&mut self.param_states[index],
&self.system_meta,
self.world,
self.change_tick,
)
}
}
/// Calls a closure for each parameter in the set.
pub fn for_each(&mut self, mut f: impl FnMut(T::Item<'_, '_>)) {
self.param_states.iter_mut().for_each(|state| {
f(
// SAFETY:
// - We initialized the state for each parameter in the builder, so the caller ensures we have access to any world data needed by any param.
// We have mutable access to the ParamSet, so no other params in the set are active.
// - The caller of `get_param` ensured that this was the world used to initialize our state, and we used that world to initialize parameter states
unsafe { T::get_param(state, &self.system_meta, self.world, self.change_tick) },
);
});
}
}
macro_rules! impl_system_param_tuple {
($(#[$meta:meta])* $($param: ident),*) => {
$(#[$meta])*
// SAFETY: tuple consists only of ReadOnlySystemParams
unsafe impl<$($param: ReadOnlySystemParam),*> ReadOnlySystemParam for ($($param,)*) {}
#[expect(
clippy::allow_attributes,
reason = "This is in a macro, and as such, the below lints may not always apply."
)]
#[allow(
non_snake_case,
reason = "Certain variable names are provided by the caller, not by us."
)]
#[allow(
unused_variables,
reason = "Zero-length tuples won't use some of the parameters."
)]
$(#[$meta])*
// SAFETY: implementors of each `SystemParam` in the tuple have validated their impls
unsafe impl<$($param: SystemParam),*> SystemParam for ($($param,)*) {
type State = ($($param::State,)*);
type Item<'w, 's> = ($($param::Item::<'w, 's>,)*);
#[inline]
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
(($($param::init_state(world, system_meta),)*))
}
#[inline]
unsafe fn new_archetype(($($param,)*): &mut Self::State, archetype: &Archetype, system_meta: &mut SystemMeta) {
#[allow(
unused_unsafe,
reason = "Zero-length tuples will not run anything in the unsafe block."
)]
// SAFETY: The caller ensures that `archetype` is from the World the state was initialized from in `init_state`.
unsafe { $($param::new_archetype($param, archetype, system_meta);)* }
}
#[inline]
fn apply(($($param,)*): &mut Self::State, system_meta: &SystemMeta, world: &mut World) {
$($param::apply($param, system_meta, world);)*
}
#[inline]
#[allow(
unused_mut,
reason = "The `world` parameter is unused for zero-length tuples; however, it must be mutable for other lengths of tuples."
)]
fn queue(($($param,)*): &mut Self::State, system_meta: &SystemMeta, mut world: DeferredWorld) {
$($param::queue($param, system_meta, world.reborrow());)*
}
#[inline]
unsafe fn validate_param(
state: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
let ($($param,)*) = state;
$($param::validate_param($param, system_meta, world)&&)* true
}
#[inline]
unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's> {
let ($($param,)*) = state;
#[allow(
clippy::unused_unit,
reason = "Zero-length tuples won't have any params to get."
)]
($($param::get_param($param, system_meta, world, change_tick),)*)
}
}
};
}
all_tuples!(
#[doc(fake_variadic)]
impl_system_param_tuple,
0,
16,
P
);
/// Contains type aliases for built-in [`SystemParam`]s with `'static` lifetimes.
/// This makes it more convenient to refer to these types in contexts where
/// explicit lifetime annotations are required.
///
/// Note that this is entirely safe and tracks lifetimes correctly.
/// This purely exists for convenience.
///
/// You can't instantiate a static `SystemParam`, you'll always end up with
/// `Res<'w, T>`, `ResMut<'w, T>` or `&'w T` bound to the lifetime of the provided
/// `&'w World`.
///
/// [`SystemParam`]: super::SystemParam
pub mod lifetimeless {
/// A [`Query`](super::Query) with `'static` lifetimes.
pub type SQuery<D, F = ()> = super::Query<'static, 'static, D, F>;
/// A shorthand for writing `&'static T`.
pub type Read<T> = &'static T;
/// A shorthand for writing `&'static mut T`.
pub type Write<T> = &'static mut T;
/// A [`Res`](super::Res) with `'static` lifetimes.
pub type SRes<T> = super::Res<'static, T>;
/// A [`ResMut`](super::ResMut) with `'static` lifetimes.
pub type SResMut<T> = super::ResMut<'static, T>;
/// [`Commands`](crate::system::Commands) with `'static` lifetimes.
pub type SCommands = crate::system::Commands<'static, 'static>;
}
/// A helper for using system parameters in generic contexts
///
/// This type is a [`SystemParam`] adapter which always has
/// `Self::Item == Self` (ignoring lifetimes for brevity),
/// no matter the argument [`SystemParam`] (`P`) (other than
/// that `P` must be `'static`)
///
/// This makes it useful for having arbitrary [`SystemParam`] type arguments
/// to function systems, or for generic types using the [`derive@SystemParam`]
/// derive:
///
/// ```
/// # use bevy_ecs::prelude::*;
/// use bevy_ecs::system::{SystemParam, StaticSystemParam};
/// #[derive(SystemParam)]
/// struct GenericParam<'w,'s, T: SystemParam + 'static> {
/// field: StaticSystemParam<'w, 's, T>,
/// }
/// fn do_thing_generically<T: SystemParam + 'static>(t: StaticSystemParam<T>) {}
///
/// fn check_always_is_system<T: SystemParam + 'static>(){
/// bevy_ecs::system::assert_is_system(do_thing_generically::<T>);
/// }
/// ```
/// Note that in a real case you'd generally want
/// additional bounds on `P`, for your use of the parameter
/// to have a reason to be generic.
///
/// For example, using this would allow a type to be generic over
/// whether a resource is accessed mutably or not, with
/// impls being bounded on [`P: Deref<Target=MyType>`](Deref), and
/// [`P: DerefMut<Target=MyType>`](DerefMut) depending on whether the
/// method requires mutable access or not.
///
/// The method which doesn't use this type will not compile:
/// ```compile_fail
/// # use bevy_ecs::prelude::*;
/// # use bevy_ecs::system::{SystemParam, StaticSystemParam};
///
/// fn do_thing_generically<T: SystemParam + 'static>(t: T) {}
///
/// #[derive(SystemParam)]
/// struct GenericParam<'w, 's, T: SystemParam> {
/// field: T,
/// // Use the lifetimes in this type, or they will be unbound.
/// phantom: std::marker::PhantomData<&'w &'s ()>
/// }
/// # fn check_always_is_system<T: SystemParam + 'static>(){
/// # bevy_ecs::system::assert_is_system(do_thing_generically::<T>);
/// # }
/// ```
pub struct StaticSystemParam<'w, 's, P: SystemParam>(SystemParamItem<'w, 's, P>);
impl<'w, 's, P: SystemParam> Deref for StaticSystemParam<'w, 's, P> {
type Target = SystemParamItem<'w, 's, P>;
fn deref(&self) -> &Self::Target {
&self.0
}
}
impl<'w, 's, P: SystemParam> DerefMut for StaticSystemParam<'w, 's, P> {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.0
}
}
impl<'w, 's, P: SystemParam> StaticSystemParam<'w, 's, P> {
/// Get the value of the parameter
pub fn into_inner(self) -> SystemParamItem<'w, 's, P> {
self.0
}
}
// SAFETY: This doesn't add any more reads, and the delegated fetch confirms it
unsafe impl<'w, 's, P: ReadOnlySystemParam + 'static> ReadOnlySystemParam
for StaticSystemParam<'w, 's, P>
{
}
// SAFETY: all methods are just delegated to `P`'s `SystemParam` implementation
unsafe impl<P: SystemParam + 'static> SystemParam for StaticSystemParam<'_, '_, P> {
type State = P::State;
type Item<'world, 'state> = StaticSystemParam<'world, 'state, P>;
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State {
P::init_state(world, system_meta)
}
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
// SAFETY: The caller guarantees that the provided `archetype` matches the World used to initialize `state`.
unsafe { P::new_archetype(state, archetype, system_meta) };
}
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World) {
P::apply(state, system_meta, world);
}
fn queue(state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld) {
P::queue(state, system_meta, world);
}
#[inline]
unsafe fn validate_param(
state: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
P::validate_param(state, system_meta, world)
}
#[inline]
unsafe fn get_param<'world, 'state>(
state: &'state mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'world>,
change_tick: Tick,
) -> Self::Item<'world, 'state> {
// SAFETY: Defer to the safety of P::SystemParam
StaticSystemParam(unsafe { P::get_param(state, system_meta, world, change_tick) })
}
}
// SAFETY: No world access.
unsafe impl<T: ?Sized> SystemParam for PhantomData<T> {
type State = ();
type Item<'world, 'state> = Self;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
#[inline]
unsafe fn get_param<'world, 'state>(
_state: &'state mut Self::State,
_system_meta: &SystemMeta,
_world: UnsafeWorldCell<'world>,
_change_tick: Tick,
) -> Self::Item<'world, 'state> {
PhantomData
}
}
// SAFETY: No world access.
unsafe impl<T: ?Sized> ReadOnlySystemParam for PhantomData<T> {}
/// A [`SystemParam`] with a type that can be configured at runtime.
///
/// To be useful, this must be configured using a [`DynParamBuilder`](crate::system::DynParamBuilder) to build the system using a [`SystemParamBuilder`](crate::prelude::SystemParamBuilder).
///
/// # Examples
///
/// ```
/// # use bevy_ecs::{prelude::*, system::*};
/// #
/// # #[derive(Default, Resource)]
/// # struct A;
/// #
/// # #[derive(Default, Resource)]
/// # struct B;
/// #
/// # let mut world = World::new();
/// # world.init_resource::<A>();
/// # world.init_resource::<B>();
/// #
/// // If the inner parameter doesn't require any special building, use `ParamBuilder`.
/// // Either specify the type parameter on `DynParamBuilder::new()` ...
/// let system = (DynParamBuilder::new::<Res<A>>(ParamBuilder),)
/// .build_state(&mut world)
/// .build_system(expects_res_a);
/// # world.run_system_once(system);
///
/// // ... or use a factory method on `ParamBuilder` that returns a specific type.
/// let system = (DynParamBuilder::new(ParamBuilder::resource::<A>()),)
/// .build_state(&mut world)
/// .build_system(expects_res_a);
/// # world.run_system_once(system);
///
/// fn expects_res_a(mut param: DynSystemParam) {
/// // Use the `downcast` methods to retrieve the inner parameter.
/// // They will return `None` if the type does not match.
/// assert!(param.is::<Res<A>>());
/// assert!(!param.is::<Res<B>>());
/// assert!(param.downcast_mut::<Res<B>>().is_none());
/// let res = param.downcast_mut::<Res<A>>().unwrap();
/// // The type parameter can be left out if it can be determined from use.
/// let res: Res<A> = param.downcast().unwrap();
/// }
///
/// let system = (
/// // If the inner parameter also requires building,
/// // pass the appropriate `SystemParamBuilder`.
/// DynParamBuilder::new(LocalBuilder(10usize)),
/// // `DynSystemParam` is just an ordinary `SystemParam`,
/// // and can be combined with other parameters as usual!
/// ParamBuilder::query(),
/// )
/// .build_state(&mut world)
/// .build_system(|param: DynSystemParam, query: Query<()>| {
/// let local: Local<usize> = param.downcast::<Local<usize>>().unwrap();
/// assert_eq!(*local, 10);
/// });
/// # world.run_system_once(system);
/// ```
pub struct DynSystemParam<'w, 's> {
/// A `ParamState<T>` wrapping the state for the underlying system param.
state: &'s mut dyn Any,
world: UnsafeWorldCell<'w>,
system_meta: SystemMeta,
change_tick: Tick,
}
impl<'w, 's> DynSystemParam<'w, 's> {
/// # Safety
/// - `state` must be a `ParamState<T>` for some inner `T: SystemParam`.
/// - The passed [`UnsafeWorldCell`] must have access to any world data registered
/// in [`init_state`](SystemParam::init_state) for the inner system param.
/// - `world` must be the same `World` that was used to initialize
/// [`state`](SystemParam::init_state) for the inner system param.
unsafe fn new(
state: &'s mut dyn Any,
world: UnsafeWorldCell<'w>,
system_meta: SystemMeta,
change_tick: Tick,
) -> Self {
Self {
state,
world,
system_meta,
change_tick,
}
}
/// Returns `true` if the inner system param is the same as `T`.
pub fn is<T: SystemParam>(&self) -> bool
// See downcast() function for an explanation of the where clause
where
T::Item<'static, 'static>: SystemParam<Item<'w, 's> = T> + 'static,
{
self.state.is::<ParamState<T::Item<'static, 'static>>>()
}
/// Returns the inner system param if it is the correct type.
/// This consumes the dyn param, so the returned param can have its original world and state lifetimes.
pub fn downcast<T: SystemParam>(self) -> Option<T>
// See downcast() function for an explanation of the where clause
where
T::Item<'static, 'static>: SystemParam<Item<'w, 's> = T> + 'static,
{
// SAFETY:
// - `DynSystemParam::new()` ensures `state` is a `ParamState<T>`, that the world matches,
// and that it has access required by the inner system param.
// - This consumes the `DynSystemParam`, so it is the only use of `world` with this access and it is available for `'w`.
unsafe { downcast::<T>(self.state, &self.system_meta, self.world, self.change_tick) }
}
/// Returns the inner system parameter if it is the correct type.
/// This borrows the dyn param, so the returned param is only valid for the duration of that borrow.
pub fn downcast_mut<'a, T: SystemParam>(&'a mut self) -> Option<T>
// See downcast() function for an explanation of the where clause
where
T::Item<'static, 'static>: SystemParam<Item<'a, 'a> = T> + 'static,
{
// SAFETY:
// - `DynSystemParam::new()` ensures `state` is a `ParamState<T>`, that the world matches,
// and that it has access required by the inner system param.
// - This exclusively borrows the `DynSystemParam` for `'_`, so it is the only use of `world` with this access for `'_`.
unsafe { downcast::<T>(self.state, &self.system_meta, self.world, self.change_tick) }
}
/// Returns the inner system parameter if it is the correct type.
/// This borrows the dyn param, so the returned param is only valid for the duration of that borrow,
/// but since it only performs read access it can keep the original world lifetime.
/// This can be useful with methods like [`Query::iter_inner()`] or [`Res::into_inner()`]
/// to obtain references with the original world lifetime.
pub fn downcast_mut_inner<'a, T: ReadOnlySystemParam>(&'a mut self) -> Option<T>
// See downcast() function for an explanation of the where clause
where
T::Item<'static, 'static>: SystemParam<Item<'w, 'a> = T> + 'static,
{
// SAFETY:
// - `DynSystemParam::new()` ensures `state` is a `ParamState<T>`, that the world matches,
// and that it has access required by the inner system param.
// - The inner system param only performs read access, so it's safe to copy that access for the full `'w` lifetime.
unsafe { downcast::<T>(self.state, &self.system_meta, self.world, self.change_tick) }
}
}
/// # Safety
/// - `state` must be a `ParamState<T>` for some inner `T: SystemParam`.
/// - The passed [`UnsafeWorldCell`] must have access to any world data registered
/// in [`init_state`](SystemParam::init_state) for the inner system param.
/// - `world` must be the same `World` that was used to initialize
/// [`state`](SystemParam::init_state) for the inner system param.
unsafe fn downcast<'w, 's, T: SystemParam>(
state: &'s mut dyn Any,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Option<T>
// We need a 'static version of the SystemParam to use with `Any::downcast_mut()`,
// and we need a <'w, 's> version to actually return.
// The type parameter T must be the one we return in order to get type inference from the return value.
// So we use `T::Item<'static, 'static>` as the 'static version, and require that it be 'static.
// That means the return value will be T::Item<'static, 'static>::Item<'w, 's>,
// so we constrain that to be equal to T.
// Every actual `SystemParam` implementation has `T::Item == T` up to lifetimes,
// so they should all work with this constraint.
where
T::Item<'static, 'static>: SystemParam<Item<'w, 's> = T> + 'static,
{
state
.downcast_mut::<ParamState<T::Item<'static, 'static>>>()
.map(|state| {
// SAFETY:
// - The caller ensures the world has access for the underlying system param,
// and since the downcast succeeded, the underlying system param is T.
// - The caller ensures the `world` matches.
unsafe { T::Item::get_param(&mut state.0, system_meta, world, change_tick) }
})
}
/// The [`SystemParam::State`] for a [`DynSystemParam`].
pub struct DynSystemParamState(Box<dyn DynParamState>);
impl DynSystemParamState {
pub(crate) fn new<T: SystemParam + 'static>(state: T::State) -> Self {
Self(Box::new(ParamState::<T>(state)))
}
}
/// Allows a [`SystemParam::State`] to be used as a trait object for implementing [`DynSystemParam`].
trait DynParamState: Sync + Send {
/// Casts the underlying `ParamState<T>` to an `Any` so it can be downcast.
fn as_any_mut(&mut self) -> &mut dyn Any;
/// For the specified [`Archetype`], registers the components accessed by this [`SystemParam`] (if applicable).a
///
/// # Safety
/// `archetype` must be from the [`World`] used to initialize `state` in [`SystemParam::init_state`].
unsafe fn new_archetype(&mut self, archetype: &Archetype, system_meta: &mut SystemMeta);
/// Applies any deferred mutations stored in this [`SystemParam`]'s state.
/// This is used to apply [`Commands`] during [`ApplyDeferred`](crate::prelude::ApplyDeferred).
///
/// [`Commands`]: crate::prelude::Commands
fn apply(&mut self, system_meta: &SystemMeta, world: &mut World);
/// Queues any deferred mutations to be applied at the next [`ApplyDeferred`](crate::prelude::ApplyDeferred).
fn queue(&mut self, system_meta: &SystemMeta, world: DeferredWorld);
/// Refer to [`SystemParam::validate_param`].
///
/// # Safety
/// Refer to [`SystemParam::validate_param`].
unsafe fn validate_param(&self, system_meta: &SystemMeta, world: UnsafeWorldCell) -> bool;
}
/// A wrapper around a [`SystemParam::State`] that can be used as a trait object in a [`DynSystemParam`].
struct ParamState<T: SystemParam>(T::State);
impl<T: SystemParam + 'static> DynParamState for ParamState<T> {
fn as_any_mut(&mut self) -> &mut dyn Any {
self
}
unsafe fn new_archetype(&mut self, archetype: &Archetype, system_meta: &mut SystemMeta) {
// SAFETY: The caller ensures that `archetype` is from the World the state was initialized from in `init_state`.
unsafe { T::new_archetype(&mut self.0, archetype, system_meta) };
}
fn apply(&mut self, system_meta: &SystemMeta, world: &mut World) {
T::apply(&mut self.0, system_meta, world);
}
fn queue(&mut self, system_meta: &SystemMeta, world: DeferredWorld) {
T::queue(&mut self.0, system_meta, world);
}
unsafe fn validate_param(&self, system_meta: &SystemMeta, world: UnsafeWorldCell) -> bool {
T::validate_param(&self.0, system_meta, world)
}
}
// SAFETY: `init_state` creates a state of (), which performs no access. The interesting safety checks are on the `SystemParamBuilder`.
unsafe impl SystemParam for DynSystemParam<'_, '_> {
type State = DynSystemParamState;
type Item<'world, 'state> = DynSystemParam<'world, 'state>;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
DynSystemParamState::new::<()>(())
}
#[inline]
unsafe fn validate_param(
state: &Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell,
) -> bool {
state.0.validate_param(system_meta, world)
}
#[inline]
unsafe fn get_param<'world, 'state>(
state: &'state mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'world>,
change_tick: Tick,
) -> Self::Item<'world, 'state> {
// SAFETY:
// - `state.0` is a boxed `ParamState<T>`, and its implementation of `as_any_mut` returns `self`.
// - The state was obtained from `SystemParamBuilder::build()`, which registers all [`World`] accesses used
// by [`SystemParam::get_param`] with the provided [`system_meta`](SystemMeta).
// - The caller ensures that the provided world is the same and has the required access.
unsafe {
DynSystemParam::new(
state.0.as_any_mut(),
world,
system_meta.clone(),
change_tick,
)
}
}
unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
) {
// SAFETY: The caller ensures that `archetype` is from the World the state was initialized from in `init_state`.
unsafe { state.0.new_archetype(archetype, system_meta) };
}
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World) {
state.0.apply(system_meta, world);
}
fn queue(state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld) {
state.0.queue(system_meta, world);
}
}
// SAFETY: When initialized with `init_state`, `get_param` returns a `FilteredResources` with no access.
// Therefore, `init_state` trivially registers all access, and no accesses can conflict.
// Note that the safety requirements for non-empty access are handled by the `SystemParamBuilder` impl that builds them.
unsafe impl SystemParam for FilteredResources<'_, '_> {
type State = Access<ComponentId>;
type Item<'world, 'state> = FilteredResources<'world, 'state>;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
Access::new()
}
unsafe fn get_param<'world, 'state>(
state: &'state mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'world>,
change_tick: Tick,
) -> Self::Item<'world, 'state> {
// SAFETY: The caller ensures that `world` has access to anything registered in `init_state` or `build`,
// and the builder registers `access` in `build`.
unsafe { FilteredResources::new(world, state, system_meta.last_run, change_tick) }
}
}
// SAFETY: FilteredResources only reads resources.
unsafe impl ReadOnlySystemParam for FilteredResources<'_, '_> {}
// SAFETY: When initialized with `init_state`, `get_param` returns a `FilteredResourcesMut` with no access.
// Therefore, `init_state` trivially registers all access, and no accesses can conflict.
// Note that the safety requirements for non-empty access are handled by the `SystemParamBuilder` impl that builds them.
unsafe impl SystemParam for FilteredResourcesMut<'_, '_> {
type State = Access<ComponentId>;
type Item<'world, 'state> = FilteredResourcesMut<'world, 'state>;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
Access::new()
}
unsafe fn get_param<'world, 'state>(
state: &'state mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'world>,
change_tick: Tick,
) -> Self::Item<'world, 'state> {
// SAFETY: The caller ensures that `world` has access to anything registered in `init_state` or `build`,
// and the builder registers `access` in `build`.
unsafe { FilteredResourcesMut::new(world, state, system_meta.last_run, change_tick) }
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::system::assert_is_system;
use core::cell::RefCell;
// Compile test for https://github.com/bevyengine/bevy/pull/2838.
#[test]
fn system_param_generic_bounds() {
#[derive(SystemParam)]
pub struct SpecialQuery<
'w,
's,
D: QueryData + Send + Sync + 'static,
F: QueryFilter + Send + Sync + 'static = (),
> {
_query: Query<'w, 's, D, F>,
}
fn my_system(_: SpecialQuery<(), ()>) {}
assert_is_system(my_system);
}
// Compile tests for https://github.com/bevyengine/bevy/pull/6694.
#[test]
fn system_param_flexibility() {
#[derive(SystemParam)]
pub struct SpecialRes<'w, T: Resource> {
_res: Res<'w, T>,
}
#[derive(SystemParam)]
pub struct SpecialLocal<'s, T: FromWorld + Send + 'static> {
_local: Local<'s, T>,
}
#[derive(Resource)]
struct R;
fn my_system(_: SpecialRes<R>, _: SpecialLocal<u32>) {}
assert_is_system(my_system);
}
#[derive(Resource)]
pub struct R<const I: usize>;
// Compile test for https://github.com/bevyengine/bevy/pull/7001.
#[test]
fn system_param_const_generics() {
#[expect(
dead_code,
reason = "This struct is used to ensure that const generics are supported as a SystemParam; thus, the inner value never needs to be read."
)]
#[derive(SystemParam)]
pub struct ConstGenericParam<'w, const I: usize>(Res<'w, R<I>>);
fn my_system(_: ConstGenericParam<0>, _: ConstGenericParam<1000>) {}
assert_is_system(my_system);
}
// Compile test for https://github.com/bevyengine/bevy/pull/6867.
#[test]
fn system_param_field_limit() {
#[derive(SystemParam)]
pub struct LongParam<'w> {
// Each field should be a distinct type so there will
// be an error if the derive messes up the field order.
_r0: Res<'w, R<0>>,
_r1: Res<'w, R<1>>,
_r2: Res<'w, R<2>>,
_r3: Res<'w, R<3>>,
_r4: Res<'w, R<4>>,
_r5: Res<'w, R<5>>,
_r6: Res<'w, R<6>>,
_r7: Res<'w, R<7>>,
_r8: Res<'w, R<8>>,
_r9: Res<'w, R<9>>,
_r10: Res<'w, R<10>>,
_r11: Res<'w, R<11>>,
_r12: Res<'w, R<12>>,
_r13: Res<'w, R<13>>,
_r14: Res<'w, R<14>>,
_r15: Res<'w, R<15>>,
_r16: Res<'w, R<16>>,
}
fn long_system(_: LongParam) {}
assert_is_system(long_system);
}
// Compile test for https://github.com/bevyengine/bevy/pull/6919.
// Regression test for https://github.com/bevyengine/bevy/issues/7447.
#[test]
fn system_param_phantom_data() {
#[derive(SystemParam)]
struct PhantomParam<'w, T: Resource, Marker: 'static> {
_foo: Res<'w, T>,
marker: PhantomData<&'w Marker>,
}
fn my_system(_: PhantomParam<R<0>, ()>) {}
assert_is_system(my_system);
}
// Compile tests for https://github.com/bevyengine/bevy/pull/6957.
#[test]
fn system_param_struct_variants() {
#[derive(SystemParam)]
pub struct UnitParam;
#[expect(
dead_code,
reason = "This struct is used to ensure that tuple structs are supported as a SystemParam; thus, the inner values never need to be read."
)]
#[derive(SystemParam)]
pub struct TupleParam<'w, 's, R: Resource, L: FromWorld + Send + 'static>(
Res<'w, R>,
Local<'s, L>,
);
fn my_system(_: UnitParam, _: TupleParam<R<0>, u32>) {}
assert_is_system(my_system);
}
// Regression test for https://github.com/bevyengine/bevy/issues/4200.
#[test]
fn system_param_private_fields() {
#[derive(Resource)]
struct PrivateResource;
#[expect(
dead_code,
reason = "This struct is used to ensure that SystemParam's derive can't leak private fields; thus, the inner values never need to be read."
)]
#[derive(SystemParam)]
pub struct EncapsulatedParam<'w>(Res<'w, PrivateResource>);
fn my_system(_: EncapsulatedParam) {}
assert_is_system(my_system);
}
// Regression test for https://github.com/bevyengine/bevy/issues/7103.
#[test]
fn system_param_where_clause() {
#[derive(SystemParam)]
pub struct WhereParam<'w, 's, D>
where
D: 'static + QueryData,
{
_q: Query<'w, 's, D, ()>,
}
fn my_system(_: WhereParam<()>) {}
assert_is_system(my_system);
}
// Regression test for https://github.com/bevyengine/bevy/issues/1727.
#[test]
fn system_param_name_collision() {
#[derive(Resource)]
pub struct FetchState;
#[derive(SystemParam)]
pub struct Collide<'w> {
_x: Res<'w, FetchState>,
}
fn my_system(_: Collide) {}
assert_is_system(my_system);
}
// Regression test for https://github.com/bevyengine/bevy/issues/8192.
#[test]
fn system_param_invariant_lifetime() {
#[derive(SystemParam)]
pub struct InvariantParam<'w, 's> {
_set: ParamSet<'w, 's, (Query<'w, 's, ()>,)>,
}
fn my_system(_: InvariantParam) {}
assert_is_system(my_system);
}
// Compile test for https://github.com/bevyengine/bevy/pull/9589.
#[test]
fn non_sync_local() {
fn non_sync_system(cell: Local<RefCell<u8>>) {
assert_eq!(*cell.borrow(), 0);
}
let mut world = World::new();
let mut schedule = crate::schedule::Schedule::default();
schedule.add_systems(non_sync_system);
schedule.run(&mut world);
}
// Regression test for https://github.com/bevyengine/bevy/issues/10207.
#[test]
fn param_set_non_send_first() {
fn non_send_param_set(mut p: ParamSet<(NonSend<*mut u8>, ())>) {
let _ = p.p0();
p.p1();
}
let mut world = World::new();
world.insert_non_send_resource(core::ptr::null_mut::<u8>());
let mut schedule = crate::schedule::Schedule::default();
schedule.add_systems((non_send_param_set, non_send_param_set, non_send_param_set));
schedule.run(&mut world);
}
// Regression test for https://github.com/bevyengine/bevy/issues/10207.
#[test]
fn param_set_non_send_second() {
fn non_send_param_set(mut p: ParamSet<((), NonSendMut<*mut u8>)>) {
p.p0();
let _ = p.p1();
}
let mut world = World::new();
world.insert_non_send_resource(core::ptr::null_mut::<u8>());
let mut schedule = crate::schedule::Schedule::default();
schedule.add_systems((non_send_param_set, non_send_param_set, non_send_param_set));
schedule.run(&mut world);
}
fn _dyn_system_param_type_inference(mut p: DynSystemParam) {
// Make sure the downcast() methods are able to infer their type parameters from the use of the return type.
// This is just a compilation test, so there is nothing to run.
let _query: Query<()> = p.downcast_mut().unwrap();
let _query: Query<()> = p.downcast_mut_inner().unwrap();
let _query: Query<()> = p.downcast().unwrap();
}
}
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