Struct Spawned 

pub struct Spawned;

A filter that only retains results the first time after the entity has been spawned.

A common use for this filter is one-time initialization.

To retain all results without filtering but still check whether they were spawned after the system last ran, use SpawnDetails instead.

Note that this includes entities that spawned before the first time this Query was run.

Deferred

Note, that entity spawns issued with Commands are visible only after deferred operations are applied, typically after the system that queued them.

Time complexity

Spawned is not ArchetypeFilter, which practically means that if query matches million entities, Spawned filter will iterate over all of them even if none of them were spawned.

For example, these two systems are roughly equivalent in terms of performance:

fn system1(query: Query<Entity, Spawned>) {
    for entity in &query { /* entity spawned */ }
}

fn system2(query: Query<(Entity, SpawnDetails)>) {
    for (entity, spawned) in &query {
        if spawned.is_spawned() { /* entity spawned */ }
    }
}

Examples

fn print_spawning_entities(query: Query<&Name, Spawned>) {
    for name in &query {
        println!("Entity spawned: {:?}", name);
    }
}

Trait Implementations

impl QueryFilter for Spawned

const IS_ARCHETYPAL: bool = false

Returns true if (and only if) this Filter relies strictly on archetypes to limit which components are accessed by the Query.

unsafe fn filter_fetch( _state: &Self::State, fetch: &mut Self::Fetch<'_>, entity: Entity, _table_row: TableRow, ) -> bool

Returns true if the provided Entity and TableRow should be included in the query results. If false, the entity will be skipped.

impl WorldQuery for Spawned

const IS_DENSE: bool = true

Returns true if (and only if) every table of every archetype matched by this fetch contains all of the matched components.

type Fetch<'w> = SpawnedFetch<'w>

Per archetype/table state retrieved by this WorldQuery to compute Self::Item for each entity.

type State = ()

State used to construct a Self::Fetch. This will be cached inside QueryState, so it is best to move as much data / computation here as possible to reduce the cost of constructing Self::Fetch.

fn shrink_fetch<'wlong: 'wshort, 'wshort>( fetch: Self::Fetch<'wlong>, ) -> Self::Fetch<'wshort>

This function manually implements subtyping for the query fetches.

unsafe fn init_fetch<'w, 's>( world: UnsafeWorldCell<'w>, _state: &'s (), last_run: Tick, this_run: Tick, ) -> Self::Fetch<'w>

Creates a new instance of Self::Fetch, by combining data from the World with the cached Self::State. Readonly accesses resources registered in WorldQuery::update_component_access.

unsafe fn set_archetype<'w, 's>( _fetch: &mut Self::Fetch<'w>, _state: &'s (), _archetype: &'w Archetype, _table: &'w Table, )

Adjusts internal state to account for the next Archetype. This will always be called on archetypes that match this WorldQuery.

unsafe fn set_table<'w, 's>( _fetch: &mut Self::Fetch<'w>, _state: &'s (), _table: &'w Table, )

Adjusts internal state to account for the next Table. This will always be called on tables that match this WorldQuery.

fn update_component_access(_state: &(), _access: &mut FilteredAccess)

Adds any component accesses used by this WorldQuery to access.

fn init_state(_world: &mut World)

Creates and initializes a State for this WorldQuery type.

fn get_state(_components: &Components) -> Option<()>

Attempts to initialize a State for this WorldQuery type using read-only access to Components.

fn matches_component_set( _state: &(), _set_contains_id: &impl Fn(ComponentId) -> bool, ) -> bool

Returns true if this query matches a set of components. Otherwise, returns false.