MessageReader

Struct MessageReader 

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pub struct MessageReader<'w, 's, E>
where E: Message,
{ /* private fields */ }
Expand description

Reads Messages of type T in order and tracks which messages have already been read.

§Concurrency

Unlike MessageWriter<T>, systems with MessageReader<T> param can be executed concurrently (but not concurrently with MessageWriter<T> or MessageMutator<T> systems for the same message type).

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impl<'w, 's, E> MessageReader<'w, 's, E>
where E: Message,

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pub fn read(&mut self) -> MessageIterator<'_, E>

Iterates over the messages this MessageReader has not seen yet. This updates the MessageReader’s message counter, which means subsequent message reads will not include messages that happened before now.

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pub fn read_with_id(&mut self) -> MessageIteratorWithId<'_, E>

Like read, except also returning the MessageId of the messages.

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pub fn par_read(&mut self) -> MessageParIter<'_, E>

Returns a parallel iterator over the messages this MessageReader has not seen yet. See also for_each.

§Example

#[derive(Message)]
struct MyMessage {
    value: usize,
}

#[derive(Resource, Default)]
struct Counter(AtomicUsize);

// setup
let mut world = World::new();
world.init_resource::<Messages<MyMessage>>();
world.insert_resource(Counter::default());

let mut schedule = Schedule::default();
schedule.add_systems(|mut messages: MessageReader<MyMessage>, counter: Res<Counter>| {
    messages.par_read().for_each(|MyMessage { value }| {
        counter.0.fetch_add(*value, Ordering::Relaxed);
    });
});
for value in 0..100 {
    world.write_message(MyMessage { value });
}
schedule.run(&mut world);
let Counter(counter) = world.remove_resource::<Counter>().unwrap();
// all messages were processed
assert_eq!(counter.into_inner(), 4950);
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pub fn len(&self) -> usize

Determines the number of messages available to be read from this MessageReader without consuming any.

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pub fn is_empty(&self) -> bool

Returns true if there are no messages available to read.

§Example

The following example shows a useful pattern where some behavior is triggered if new messages are available. MessageReader::clear() is used so the same messages don’t re-trigger the behavior the next time the system runs.

#[derive(Message)]
struct Collision;

fn play_collision_sound(mut messages: MessageReader<Collision>) {
    if !messages.is_empty() {
        messages.clear();
        // Play a sound
    }
}
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pub fn clear(&mut self)

Consumes all available messages.

This means these messages will not appear in calls to MessageReader::read() or MessageReader::read_with_id() and MessageReader::is_empty() will return true.

For usage, see MessageReader::is_empty().

Trait Implementations§

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impl<'w, 's, E> Debug for MessageReader<'w, 's, E>
where E: Debug + Message,

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

Formats the value using the given formatter. Read more
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impl<E> SystemParam for MessageReader<'_, '_, E>
where E: Message,

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type State = FetchState<E>

Used to store data which persists across invocations of a system.
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type Item<'w, 's> = MessageReader<'w, 's, E>

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, ) -> <MessageReader<'_, '_, E> as SystemParam>::State

Creates a new instance of this param’s State.
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fn init_access( state: &<MessageReader<'_, '_, E> as SystemParam>::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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fn apply( state: &mut <MessageReader<'_, '_, E> as SystemParam>::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 <MessageReader<'_, '_, E> as SystemParam>::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<'w, 's>( state: &'s mut <MessageReader<'_, '_, E> as SystemParam>::State, _system_meta: &SystemMeta, _world: UnsafeWorldCell<'w>, ) -> Result<(), SystemParamValidationError>

Validates that the param can be acquired by the get_param. Read more
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unsafe fn get_param<'w, 's>( state: &'s mut <MessageReader<'_, '_, E> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick, ) -> <MessageReader<'_, '_, E> as SystemParam>::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction. Read more
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impl<'w, 's, E> ReadOnlySystemParam for MessageReader<'w, 's, E>

Auto Trait Implementations§

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impl<'w, 's, E> Freeze for MessageReader<'w, 's, E>

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impl<'w, 's, E> RefUnwindSafe for MessageReader<'w, 's, E>
where E: RefUnwindSafe,

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impl<'w, 's, E> Send for MessageReader<'w, 's, E>

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impl<'w, 's, E> Sync for MessageReader<'w, 's, E>

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impl<'w, 's, E> Unpin for MessageReader<'w, 's, E>

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impl<'w, 's, E> !UnwindSafe for MessageReader<'w, 's, E>

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, U> AsBindGroupShaderType<U> for T
where U: ShaderType, &'a T: for<'a> Into<U>,

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fn as_bind_group_shader_type(&self, _images: &RenderAssets<GpuImage>) -> U

Return the T ShaderType for self. When used in AsBindGroup derives, it is safe to assume that all images in self exist.
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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> Downcast for T
where T: Any,

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

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

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

Convert &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)

Convert &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> DowncastSync for T
where T: Any + Send + Sync,

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fn into_any_arc(self: Arc<T>) -> Arc<dyn Any + Sync + Send>

Convert Arc<Trait> (where Trait: Downcast) to Arc<Any>. Arc<Any> can then be further downcast into Arc<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, W> HasTypeWitness<W> for T
where W: MakeTypeWitness<Arg = T>, T: ?Sized,

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const WITNESS: W = W::MAKE

A constant of the type witness
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impl<T> Identity for T
where T: ?Sized,

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const TYPE_EQ: TypeEq<T, <T as Identity>::Type> = TypeEq::NEW

Proof that Self is the same type as Self::Type, provides methods for casting between Self and Self::Type.
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type Type = T

The same type as Self, used to emulate type equality bounds (T == U) with associated type equality constraints (T: Identity<Type = U>).
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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> IntoEither for T

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fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts self into a Left variant of Either<Self, Self> if into_left is true. Converts self into a Right variant of Either<Self, Self> otherwise. Read more
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fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts self into a Left variant of Either<Self, Self> if into_left(&self) returns true. Converts self into a Right variant of Either<Self, Self> otherwise. Read more
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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<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<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> Settings for T
where T: 'static + Send + Sync,

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impl<T> WasmNotSend for T
where T: Send,

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impl<T> WasmNotSendSync for T

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impl<T> WasmNotSync for T
where T: Sync,