Local

Struct Local 

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pub struct Local<'s, T: FromWorld + Send + 'static>(/* private fields */);
Expand description

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 SystemParams within the same system each specify the same local type each will get their own distinct data storage.

The supplied lifetime parameter is the SystemParams 's lifetime.

§Examples

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).unwrap(), 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).unwrap(), 0);

A simple way to set a different default value for a local is by wrapping the value with an Option.

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).unwrap(), 11);
// Counter is only increased by 1 on subsequent runs.
assert_eq!(counter_system.run((), world).unwrap(), 12);

N.B. A Locals 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:

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))

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impl<'s, T: Debug + FromWorld + Send + 'static> Debug for Local<'s, T>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl<'s, T: FromWorld + Send + 'static> Deref for Local<'s, T>

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type Target = T

The resulting type after dereferencing.
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fn deref(&self) -> &Self::Target

Dereferences the value.
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impl<'s, T: FromWorld + Send + 'static> DerefMut for Local<'s, T>

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fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.
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impl<'_s, T: FromWorld + Send + 'static> ExclusiveSystemParam for Local<'_s, T>

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type State = SyncCell<T>

Used to store data which persists across invocations of a system.
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type Item<'s> = Local<'s, T>

The item type returned when constructing this system param. See SystemParam::Item.
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fn init(world: &mut World, _system_meta: &mut SystemMeta) -> Self::State

Creates a new instance of this param’s State.
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fn get_param<'s>( state: &'s mut Self::State, _system_meta: &SystemMeta, ) -> Self::Item<'s>

Creates a parameter to be passed into an ExclusiveSystemParamFunction.
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impl<'s, 'a, T: FromWorld + Send + 'static> IntoIterator for &'a Local<'s, T>

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type Item = <&'a T as IntoIterator>::Item

The type of the elements being iterated over.
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type IntoIter = <&'a T as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?
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fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value. Read more
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impl<'s, 'a, T: FromWorld + Send + 'static> IntoIterator for &'a mut Local<'s, T>

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type Item = <&'a mut T as IntoIterator>::Item

The type of the elements being iterated over.
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type IntoIter = <&'a mut T as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?
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fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value. Read more
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impl<'a, T: FromWorld + Send + 'static> SystemParam for Local<'a, T>

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type State = SyncCell<T>

Used to store data which persists across invocations of a system.
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type Item<'w, 's> = Local<'s, T>

The item type returned when constructing this system param. The value of this associated type should be Self, instantiated with new lifetimes. Read more
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fn init_state(world: &mut World) -> Self::State

Creates a new instance of this param’s State.
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fn init_access( _state: &Self::State, _system_meta: &mut SystemMeta, _component_access_set: &mut FilteredAccessSet, _world: &mut World, )

Registers any World access used by this SystemParam
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unsafe fn get_param<'w, 's>( state: &'s mut Self::State, _system_meta: &SystemMeta, _world: UnsafeWorldCell<'w>, _change_tick: Tick, ) -> Self::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction. Read more
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fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World)

Applies any deferred mutations stored in this SystemParam’s state. This is used to apply Commands during ApplyDeferred.
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fn queue( state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld<'_>, )

Queues any deferred mutations to be applied at the next ApplyDeferred.
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unsafe fn validate_param( state: &mut Self::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'_>, ) -> Result<(), SystemParamValidationError>

Validates that the param can be acquired by the get_param. Read more
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impl<'s, T: FromWorld + Send + 'static> SystemParamBuilder<Local<'s, T>> for LocalBuilder<T>

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fn build(self, _world: &mut World) -> <Local<'s, T> as SystemParam>::State

Registers any World access used by this SystemParam and creates a new instance of this param’s State.
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fn build_state(self, world: &mut World) -> SystemState<P>

Create a SystemState from a SystemParamBuilder. To create a system, call SystemState::build_system on the result.
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impl<'s, T: FromWorld + Send + 'static> ReadOnlySystemParam for Local<'s, T>

Auto Trait Implementations§

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impl<'s, T> Freeze for Local<'s, T>

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impl<'s, T> RefUnwindSafe for Local<'s, T>
where T: RefUnwindSafe,

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impl<'s, T> Send for Local<'s, T>

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impl<'s, T> Sync for Local<'s, T>
where T: Sync,

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impl<'s, T> Unpin for Local<'s, T>

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impl<'s, T> !UnwindSafe for Local<'s, T>

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> Downcast for T
where T: Any,

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fn into_any(self: Box<T>) -> Box<dyn Any>

Converts Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>, which can then be downcast into Box<dyn ConcreteType> where ConcreteType implements Trait.
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fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>

Converts Rc<Trait> (where Trait: Downcast) to Rc<Any>, which can then be further downcast into Rc<ConcreteType> where ConcreteType implements Trait.
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fn as_any(&self) -> &(dyn Any + 'static)

Converts &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s.
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fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)

Converts &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s.
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impl<T> DowncastSend for T
where T: Any + Send,

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fn into_any_send(self: Box<T>) -> Box<dyn Any + Send>

Converts Box<Trait> (where Trait: DowncastSend) to Box<dyn Any + Send>, which can then be downcast into Box<ConcreteType> where ConcreteType implements Trait.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> IntoResult<T> for T

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fn into_result(self) -> Result<T, RunSystemError>

Converts this type into the system output type.
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impl<A> Is for A
where A: Any,

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fn is<T>() -> bool
where T: Any,

Checks if the current type “is” another type, using a TypeId equality comparison. This is most useful in the context of generic logic. Read more
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impl<P, T> Receiver for P
where P: Deref<Target = T> + ?Sized, T: ?Sized,

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type Target = T

🔬This is a nightly-only experimental API. (arbitrary_self_types)
The target type on which the method may be called.
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impl<R> Rng for R
where R: RngCore + ?Sized,

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fn random<T>(&mut self) -> T

Return a random value via the StandardUniform distribution. Read more
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fn random_iter<T>(self) -> Iter<StandardUniform, Self, T>

Return an iterator over random variates Read more
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fn random_range<T, R>(&mut self, range: R) -> T
where T: SampleUniform, R: SampleRange<T>,

Generate a random value in the given range. Read more
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fn random_bool(&mut self, p: f64) -> bool

Return a bool with a probability p of being true. Read more
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fn random_ratio(&mut self, numerator: u32, denominator: u32) -> bool

Return a bool with a probability of numerator/denominator of being true. Read more
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fn sample<T, D>(&mut self, distr: D) -> T
where D: Distribution<T>,

Sample a new value, using the given distribution. Read more
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fn sample_iter<T, D>(self, distr: D) -> Iter<D, Self, T>
where D: Distribution<T>, Self: Sized,

Create an iterator that generates values using the given distribution. Read more
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fn fill<T>(&mut self, dest: &mut T)
where T: Fill + ?Sized,

Fill any type implementing Fill with random data Read more
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fn gen<T>(&mut self) -> T

👎Deprecated since 0.9.0: Renamed to random to avoid conflict with the new gen keyword in Rust 2024.
Alias for Rng::random.
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fn gen_range<T, R>(&mut self, range: R) -> T
where T: SampleUniform, R: SampleRange<T>,

👎Deprecated since 0.9.0: Renamed to random_range
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fn gen_bool(&mut self, p: f64) -> bool

👎Deprecated since 0.9.0: Renamed to random_bool
Alias for Rng::random_bool.
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fn gen_ratio(&mut self, numerator: u32, denominator: u32) -> bool

👎Deprecated since 0.9.0: Renamed to random_ratio
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impl<T> RngCore for T
where T: DerefMut, <T as Deref>::Target: RngCore,

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fn next_u32(&mut self) -> u32

Return the next random u32. Read more
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fn next_u64(&mut self) -> u64

Return the next random u64. Read more
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fn fill_bytes(&mut self, dst: &mut [u8])

Fill dest with random data. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<R> TryRngCore for R
where R: RngCore + ?Sized,

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type Error = Infallible

The type returned in the event of a RNG error.
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fn try_next_u32(&mut self) -> Result<u32, <R as TryRngCore>::Error>

Return the next random u32.
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fn try_next_u64(&mut self) -> Result<u64, <R as TryRngCore>::Error>

Return the next random u64.
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fn try_fill_bytes( &mut self, dst: &mut [u8], ) -> Result<(), <R as TryRngCore>::Error>

Fill dest entirely with random data.
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fn unwrap_err(self) -> UnwrapErr<Self>
where Self: Sized,

Wrap RNG with the UnwrapErr wrapper.
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fn unwrap_mut(&mut self) -> UnwrapMut<'_, Self>

Wrap RNG with the UnwrapMut wrapper.
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fn read_adapter(&mut self) -> RngReadAdapter<'_, Self>
where Self: Sized,

Convert an RngCore to a RngReadAdapter.
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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more
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impl<T> ConditionalSend for T
where T: Send,

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impl<T> CryptoRng for T
where T: DerefMut, <T as Deref>::Target: CryptoRng,

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impl<R> TryCryptoRng for R
where R: CryptoRng + ?Sized,