Struct Local

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

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), 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.

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 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))

Trait Implementations

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

where T: Debug + FromWorld + Send + 'static,

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

Formats the value using the given formatter.

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

where T: FromWorld + Send + 'static,

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &<Local<'s, T> as Deref>::Target

Dereferences the value.

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

where T: FromWorld + Send + 'static,

fn deref_mut(&mut self) -> &mut <Local<'s, T> as Deref>::Target

Mutably dereferences the value.

impl<'_s, T> ExclusiveSystemParam for Local<'_s, T>

where T: FromWorld + Send + 'static,

type State = SyncCell<T>

Used to store data which persists across invocations of a system.

type Item<'s> = Local<'s, T>

The item type returned when constructing this system param. See SystemParam::Item.

fn init( world: &mut World, _system_meta: &mut SystemMeta, ) -> <Local<'_s, T> as ExclusiveSystemParam>::State

Creates a new instance of this param’s State.

fn get_param<'s>( state: &'s mut <Local<'_s, T> as ExclusiveSystemParam>::State, _system_meta: &SystemMeta, ) -> <Local<'_s, T> as ExclusiveSystemParam>::Item<'s>

Creates a parameter to be passed into an ExclusiveSystemParamFunction.

impl<'s, 'a, T> IntoIterator for &'a Local<'s, T>

where T: FromWorld + Send + 'static, &'a T: IntoIterator,

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

The type of the elements being iterated over.

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

Which kind of iterator are we turning this into?

fn into_iter(self) -> <&'a Local<'s, T> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'s, 'a, T> IntoIterator for &'a mut Local<'s, T>

where T: FromWorld + Send + 'static, &'a mut T: IntoIterator,

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

The type of the elements being iterated over.

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

Which kind of iterator are we turning this into?

fn into_iter(self) -> <&'a mut Local<'s, T> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'a, T> SystemParam for Local<'a, T>

where T: FromWorld + Send + 'static,

type State = SyncCell<T>

Used to store data which persists across invocations of a system.

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.

fn init_state( world: &mut World, _system_meta: &mut SystemMeta, ) -> <Local<'a, T> as SystemParam>::State

Registers any World access used by this SystemParam and creates a new instance of this param’s State.

unsafe fn get_param<'w, 's>( state: &'s mut <Local<'a, T> as SystemParam>::State, _system_meta: &SystemMeta, _world: UnsafeWorldCell<'w>, _change_tick: Tick, ) -> <Local<'a, T> as SystemParam>::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction.

unsafe fn new_archetype( state: &mut Self::State, archetype: &Archetype, system_meta: &mut SystemMeta, )

For the specified Archetype, registers the components accessed by this SystemParam (if applicable).a

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.

fn queue( state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld<'_>, )

Queues any deferred mutations to be applied at the next ApplyDeferred.

unsafe fn validate_param( state: &Self::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'_>, ) -> Result<(), SystemParamValidationError>

Validates that the param can be acquired by the get_param.

impl<'s, T> SystemParamBuilder<Local<'s, T>> for LocalBuilder<T>

where T: FromWorld + Send + 'static,

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

Registers any World access used by this SystemParam and creates a new instance of this param’s State.

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.

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

where T: FromWorld + Send + 'static,