Struct RemovedComponents 

pub struct RemovedComponents<'w, 's, T>
where
    T: Component,
{ /* private fields */ }

A [SystemParam] that yields entities that had their T Component removed or have been despawned with it.

This acts effectively the same as a MessageReader.

Unlike hooks or observers (see the lifecycle module docs), this does not allow you to see which data existed before removal.

If you are using bevy_ecs as a standalone crate, note that the RemovedComponents list will not be automatically cleared for you, and will need to be manually flushed using World::clear_trackers.

For users of bevy and bevy_app, World::clear_trackers is automatically called by bevy_app::App::update and bevy_app::SubApp::update. For the main world, this is delayed until after all SubApps have run.

Examples

Basic usage:

fn react_on_removal(mut removed: RemovedComponents<MyComponent>) {
    removed.read().for_each(|removed_entity| println!("{}", removed_entity));
}

Implementations

impl<'w, 's, T> RemovedComponents<'w, 's, T>

where T: Component,

pub fn reader(&self) -> &MessageCursor<RemovedComponentEntity>

Fetch underlying [MessageCursor].

pub fn reader_mut(&mut self) -> &mut MessageCursor<RemovedComponentEntity>

Fetch underlying [MessageCursor] mutably.

pub fn messages(&self) -> Option<&Messages<RemovedComponentEntity>>

Fetch underlying Messages.

pub fn reader_mut_with_messages( &mut self, ) -> Option<(&mut RemovedComponentReader<T>, &Messages<RemovedComponentEntity>)>

Destructures to get a mutable reference to the MessageCursor and a reference to Messages.

This is necessary since Rust can’t detect destructuring through methods and most usecases of the reader uses the Messages as well.

pub fn read( &mut self, ) -> Map<Flatten<IntoIter<Cloned<MessageIterator<'_, RemovedComponentEntity>>>>, fn(RemovedComponentEntity) -> Entity>

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

pub fn read_with_id( &mut self, ) -> Map<Flatten<IntoIter<MessageIteratorWithId<'_, RemovedComponentEntity>>>, fn((&RemovedComponentEntity, MessageId<RemovedComponentEntity>)) -> (Entity, MessageId<RemovedComponentEntity>)>

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

pub fn len(&self) -> usize

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

pub fn is_empty(&self) -> bool

Returns true if there are no messages available to read.

pub fn clear(&mut self)

Consumes all available messages.

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

Trait Implementations

impl<T> SystemParam for RemovedComponents<'_, '_, T>

where T: Component,

type State = FetchState<T>

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

type Item<'w, 's> = RemovedComponents<'w, '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, ) -> <RemovedComponents<'_, '_, T> as SystemParam>::State

Creates a new instance of this param’s State.

fn init_access( state: &<RemovedComponents<'_, '_, T> as SystemParam>::State, system_meta: &mut SystemMeta, component_access_set: &mut FilteredAccessSet, world: &mut World, )

Registers any World access used by this [SystemParam].

fn apply( state: &mut <RemovedComponents<'_, '_, T> 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.

fn queue( state: &mut <RemovedComponents<'_, '_, T> as SystemParam>::State, system_meta: &SystemMeta, world: DeferredWorld<'_>, )

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

unsafe fn get_param<'w, 's>( state: &'s mut <RemovedComponents<'_, '_, T> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick, ) -> Result<<RemovedComponents<'_, '_, T> as SystemParam>::Item<'w, 's>, SystemParamValidationError>

Creates a parameter to be passed into a SystemParamFunction.

impl<'w, 's, T> ReadOnlySystemParam for RemovedComponents<'w, 's, T>

where T: Component, ComponentIdFor<'s, T>: ReadOnlySystemParam, Local<'s, RemovedComponentReader<T>>: ReadOnlySystemParam, &'w RemovedComponentMessages: ReadOnlySystemParam,