Struct Ref

pub struct Ref<'w, T>
where
    T: ?Sized,
{ /* private fields */ }

Shared borrow of an entity’s component with access to change detection. Similar to Mut but is immutable and so doesn’t require unique access.

Examples

These two systems produce the same output.

fn how_many_changed_1(query: Query<(), Changed<MyComponent>>) {
    println!("{} changed", query.iter().count());
}

fn how_many_changed_2(query: Query<Ref<MyComponent>>) {
    println!("{} changed", query.iter().filter(|c| c.is_changed()).count());
}

Implementations

impl<'w, T> Ref<'w, T>

where T: ?Sized,

pub fn into_inner(self) -> &'w T

Returns the reference wrapped by this type. The reference is allowed to outlive self, which makes this method more flexible than simply borrowing self.

pub fn map<U>(self, f: impl FnOnce(&T) -> &U) -> Ref<'w, U>

where U: ?Sized,

Map Ref to a different type using f.

This doesn’t do anything else than call f on the wrapped value. This is equivalent to Mut::map_unchanged.

pub fn new( value: &'w T, added: &'w Tick, changed: &'w Tick, last_run: Tick, this_run: Tick, caller: &'static Location<'static>, ) -> Ref<'w, T>

Create a new Ref using provided values.

This is an advanced feature, Refs are designed to be created by engine-internal code and consumed by end-user code.

• value - The value wrapped by Ref.
• added - A Tick that stores the tick when the wrapped value was created.
• changed - A Tick that stores the last time the wrapped value was changed.
• last_run - A Tick, occurring before this_run, which is used as a reference to determine whether the wrapped value is newly added or changed.
• this_run - A Tick corresponding to the current point in time – “now”.

Trait Implementations

impl<'w, T> AsRef<T> for Ref<'w, T>

fn as_ref(&self) -> &T

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

impl<'w, T> Debug for Ref<'w, T>

where T: Debug + ?Sized,

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

Formats the value using the given formatter.

impl<'w, T> Deref for Ref<'w, T>

where T: ?Sized,

type Target = T

The resulting type after dereferencing.

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

Dereferences the value.

impl<'w, T> DetectChanges for Ref<'w, T>

where T: ?Sized,

fn is_added(&self) -> bool

Returns true if this value was added after the system last ran.

fn is_changed(&self) -> bool

Returns true if this value was added or mutably dereferenced either since the last time the system ran or, if the system never ran, since the beginning of the program.

fn last_changed(&self) -> Tick

Returns the change tick recording the time this data was most recently changed.

fn changed_by(&self) -> &'static Location<'static>

Available on crate feature track_change_detection only.

The location that last caused this to change.

impl<'w, T> From<Mut<'w, T>> for Ref<'w, T>

where T: ?Sized,

fn from(mut_ref: Mut<'w, T>) -> Ref<'w, T>

Converts to this type from the input type.

impl<'w, T> From<Res<'w, T>> for Ref<'w, T>

where T: Resource,

fn from(res: Res<'w, T>) -> Ref<'w, T>

Convert a Res into a Ref. This allows keeping the change-detection feature of Ref while losing the specificity of Res for resources.

impl<'w, 'a, T> IntoIterator for &'a Ref<'w, T>

where &'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 Ref<'w, T> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'__w, T> QueryData for Ref<'__w, T>

where T: Component,

SAFETY: Self is the same as Self::ReadOnly

type ReadOnly = Ref<'__w, T>

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

impl<'__w, T> WorldQuery for Ref<'__w, T>

where T: Component,

SAFETY: fetch accesses a single component in a readonly way. This is sound because update_component_access and update_archetype_component_access add read access for that component and panic when appropriate. update_component_access adds a With filter for a component. This is sound because matches_component_set returns whether the set contains that component.

const IS_DENSE: bool

Returns true if (and only if) every table of every archetype matched by this fetch contains all of the matched components. This is used to select a more efficient “table iterator” for “dense” queries. If this returns true, WorldQuery::set_table must be used before WorldQuery::fetch can be called for iterators. If this returns false, WorldQuery::set_archetype must be used before WorldQuery::fetch can be called for iterators.

type Item<'w> = Ref<'w, T>

The item returned by this WorldQuery For QueryData this will be the item returned by the query. For QueryFilter this will be either (), or a bool indicating whether the entity should be included or a tuple of such things.

type Fetch<'w> = RefFetch<'w, T>

Per archetype/table state used by this WorldQuery to fetch Self::Item

type State = ComponentId

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<'wlong, 'wshort>(item: Ref<'wlong, T>) -> Ref<'wshort, T>

where 'wlong: 'wshort,

This function manually implements subtyping for the query items.

fn shrink_fetch<'wlong, 'wshort>( fetch: <Ref<'__w, T> as WorldQuery>::Fetch<'wlong>, ) -> <Ref<'__w, T> as WorldQuery>::Fetch<'wshort>

where 'wlong: 'wshort,

This function manually implements subtyping for the query fetches.

unsafe fn init_fetch<'w>( world: UnsafeWorldCell<'w>, _: &ComponentId, last_run: Tick, this_run: Tick, ) -> RefFetch<'w, T>

Creates a new instance of this fetch.

unsafe fn set_archetype<'w>( fetch: &mut RefFetch<'w, T>, component_id: &ComponentId, _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 RefFetch<'w, T>, _: &ComponentId, table: &'w Table, )

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

unsafe fn fetch<'w>( fetch: &mut <Ref<'__w, T> as WorldQuery>::Fetch<'w>, entity: Entity, table_row: TableRow, ) -> <Ref<'__w, T> as WorldQuery>::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 a entity in the current archetype.

fn update_component_access( _: &ComponentId, access: &mut FilteredAccess<ComponentId>, )

Adds any component accesses used by this WorldQuery to access.

fn init_state(world: &mut World) -> ComponentId

Creates and initializes a State for this WorldQuery type.

fn get_state( components: &Components, ) -> Option<<Ref<'__w, T> as WorldQuery>::State>

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

fn matches_component_set( _: &ComponentId, 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<'__w, T> ReadOnlyQueryData for Ref<'__w, T>

where T: Component,

SAFETY: access is read only