Struct InstanceRef

pub struct InstanceRef<'a, T: Component>(/* private fields */);

A QueryData item which represents a reference to an Instance<T> and its associated Component.

This is analogous to a (Instance<T>, &T) query.

Usage

If a Kind is also a component, it is often convenient to access the instance and component data together. This type is designed to make these queries more ergonomic.

You may use this type as either a Query parameter, or access it from an EntityRef.

Example

#[derive(Component)]
struct Apple {
    freshness: f32,
}

impl Apple {
    fn is_fresh(&self) -> bool {
        self.freshness >= 0.5
    }
}

// Query Access:
fn fresh_apples(query: Query<InstanceRef<Apple>>) -> Vec<Instance<Apple>> {
    query.iter()
        .filter_map(|apple| apple.is_fresh().then_some(apple.instance()))
        .collect()
}

// Entity Access:
fn fresh_apples_world<'a>(world: &'a World) -> Vec<InstanceRef<'a, Apple>> {
   world.iter_entities()
        .filter_map(|entity| InstanceRef::from_entity(entity))
        .collect()
}

Implementations

impl<'a, T: Component> InstanceRef<'a, T>

pub fn from_entity(entity: EntityRef<'a>) -> Option<Self>

Creates a new InstanceRef<T> from an EntityRef if it contains a given Component of type T.

Trait Implementations

impl<T: Component> AsRef<Instance<T>> for InstanceRef<'_, T>

fn as_ref(&self) -> &Instance<T>

Converts this type into a shared reference of the (usually inferred) input type.

impl<T: Component> AsRef<T> for InstanceRef<'_, T>

fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.

impl<T: Component> Clone for InstanceRef<'_, T>

fn clone(&self) -> Self

Returns a duplicate of the value.

const fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Component> ContainsInstance<T> for InstanceRef<'_, T>

fn instance(&self) -> Instance<T>

Returns the associated Instance<T>.

fn entity(&self) -> Entity

Returns the Entity of the associated Instance<T>.

impl<T: Component> Deref for InstanceRef<'_, T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<T: Component> From<&InstanceRef<'_, T>> for Instance<T>

fn from(item: &InstanceRef<'_, T>) -> Self

Converts to this type from the input type.

impl<T: Component> From<InstanceRef<'_, T>> for Instance<T>

fn from(item: InstanceRef<'_, T>) -> Self

Converts to this type from the input type.

impl<T: Component> PartialEq for InstanceRef<'_, T>

fn eq(&self, other: &Self) -> bool

Tests for self and other values to be equal, and is used by ==.

const fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: Component> QueryData for InstanceRef<'_, T>

const IS_READ_ONLY: bool = true

True if this query is read-only and may not perform mutable access.

type ReadOnly = InstanceRef<'_, T>

The read-only variant of this QueryData, which satisfies the ReadOnlyQueryData trait.

type Item<'a> = InstanceRef<'a, T>

The item returned by this WorldQuery This will be the data retrieved by the query, and is visible to the end user when calling e.g. Query<Self>::get.

fn shrink<'wlong: 'wshort, 'wshort>( item: Self::Item<'wlong>, ) -> Self::Item<'wshort>

This function manually implements subtyping for the query items.

unsafe fn fetch<'w>( fetch: &mut Self::Fetch<'w>, entity: Entity, table_row: TableRow, ) -> Self::Item<'w>

Fetch Self::Item for either the given entity in the current Table, or for the given entity in the current Archetype. This must always be called after WorldQuery::set_table with a table_row in the range of the current Table or after WorldQuery::set_archetype with an entity in the current archetype. Accesses components registered in WorldQuery::update_component_access.

impl<T: Component> WorldQuery for InstanceRef<'_, T>

const IS_DENSE: bool = <(Instance<T>, &T) as WorldQuery>::IS_DENSE

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

type Fetch<'w> = <(Instance<T>, &'static T) as WorldQuery>::Fetch<'w>

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

type State = <(Instance<T>, &'static T) as WorldQuery>::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>( world: UnsafeWorldCell<'w>, state: &Self::State, 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>( fetch: &mut Self::Fetch<'w>, state: &Self::State, 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>( fetch: &mut Self::Fetch<'w>, state: &Self::State, 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: &Self::State, access: &mut FilteredAccess<ComponentId>, )

Adds any component accesses used by this WorldQuery to access.

fn init_state(world: &mut World) -> Self::State

Creates and initializes a State for this WorldQuery type.

fn get_state(components: &Components) -> Option<Self::State>

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

fn matches_component_set( state: &Self::State, set_contains_id: &impl Fn(ComponentId) -> bool, ) -> bool

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

fn set_access(_state: &mut Self::State, _access: &FilteredAccess<ComponentId>)

Sets available accesses for implementors with dynamic access such as FilteredEntityRef or FilteredEntityMut.

impl<T: Component> Copy for InstanceRef<'_, T>

impl<T: Component> Eq for InstanceRef<'_, T>

impl<T: Component> ReadOnlyQueryData for InstanceRef<'_, T>