Struct Entity 

pub struct Entity { /* private fields */ }

Lightweight identifier of an entity.

The identifier is implemented using a generational index: a combination of an index and a generation. This allows fast insertion after data removal in an array while minimizing loss of spatial locality.

Usage

This data type is returned by iterating a Query that has Entity as part of its query fetch type parameter (learn more). It can also be obtained by calling EntityCommands::id or EntityMut::id.

fn setup(mut commands: Commands) {
    // Calling `spawn` returns `EntityCommands`.
    let entity = commands.spawn(SomeComponent).id();
}

fn exclusive_system(world: &mut World) {
    // Calling `spawn` returns `EntityMut`.
    let entity = world.spawn(SomeComponent).id();
}

It can be used to refer to a specific entity to apply EntityCommands, or to call Query::get (or similar methods) to access its components.

fn dispose_expired_food(mut commands: Commands, query: Query<Entity, With<Expired>>) {
    for food_entity in &query {
        commands.entity(food_entity).despawn();
    }
}

Implementations

impl Entity

pub const fn from_raw(index: u32) -> Entity

Creates a new entity reference with the specified index and a generation of 0.

Note

Spawning a specific entity value is rarely the right choice. Most apps should favor Commands::spawn. This method should generally only be used for sharing entities across apps, and only when they have a scheme worked out to share an index space (which doesn’t happen by default).

In general, one should not try to synchronize the ECS by attempting to ensure that Entity lines up between instances, but instead insert a secondary identifier as a component.

There are still some use cases where it might be appropriate to use this function externally.

Examples

Initializing a collection (e.g. array or Vec) with a known size:

// Create a new array of size 10 and initialize it with (invalid) entities.
let mut entities: [Entity; 10] = [Entity::from_raw(0); 10];

// ... replace the entities with valid ones.

Deriving Reflect for a component that has an Entity field:

#[derive(Reflect, Component)]
#[reflect(Component)]
pub struct MyStruct {
    pub entity: Entity,
}

impl FromWorld for MyStruct {
    fn from_world(_world: &mut World) -> Self {
        Self {
            entity: Entity::from_raw(u32::MAX),
        }
    }
}

pub const fn to_bits(self) -> u64

Convert to a form convenient for passing outside of rust.

Only useful for identifying entities within the same instance of an application. Do not use for serialization between runs.

No particular structure is guaranteed for the returned bits.

pub const fn from_bits(bits: u64) -> Entity

Reconstruct an Entity previously destructured with Entity::to_bits.

Only useful when applied to results from to_bits in the same instance of an application.

pub const fn index(self) -> u32

Return a transiently unique identifier.

No two simultaneously-live entities share the same index, but dead entities’ indices may collide with both live and dead entities. Useful for compactly representing entities within a specific snapshot of the world, such as when serializing.

pub const fn generation(self) -> u32

Returns the generation of this Entity’s index. The generation is incremented each time an entity with a given index is despawned. This serves as a “count” of the number of times a given index has been reused (index, generation) pairs uniquely identify a given Entity.

Trait Implementations

impl Clone for Entity

fn clone(&self) -> Entity

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Entity

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Entity

fn deserialize<__D>( __deserializer: __D, ) -> Result<Entity, <__D as Deserializer<'de>>::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl FromReflect for Entity

fn from_reflect(reflect: &(dyn Reflect + 'static)) -> Option<Entity>

Constructs a concrete instance of Self from a reflected value.

impl GetTypeRegistration for Entity

fn get_type_registration() -> TypeRegistration

impl Hash for Entity

fn hash<__H>(&self, state: &mut __H)

where __H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Entity

fn cmp(&self, other: &Entity) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for Entity

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

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

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 PartialOrd for Entity

fn partial_cmp(&self, other: &Entity) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

Tests less than (for self and other) and is used by the < operator.

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

Tests less than or equal to (for self and other) and is used by the <= operator.

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

Tests greater than (for self and other) and is used by the > operator.

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

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Reflect for Entity

fn type_name(&self) -> &str

Returns the type name of the underlying type.

fn get_type_info(&self) -> &'static TypeInfo

Returns the TypeInfo of the underlying type.

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

Returns the value as a Box<dyn Any>.

fn as_any(&self) -> &(dyn Any + 'static)

Returns the value as a &dyn Any.

fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)

Returns the value as a &mut dyn Any.

fn into_reflect(self: Box<Entity>) -> Box<dyn Reflect>

Casts this type to a boxed reflected value.

fn as_reflect(&self) -> &(dyn Reflect + 'static)

Casts this type to a reflected value.

fn as_reflect_mut(&mut self) -> &mut (dyn Reflect + 'static)

Casts this type to a mutable reflected value.

fn clone_value(&self) -> Box<dyn Reflect>

Clones the value as a Reflect trait object.

fn apply(&mut self, value: &(dyn Reflect + 'static))

Applies a reflected value to this value.

fn set(&mut self, value: Box<dyn Reflect>) -> Result<(), Box<dyn Reflect>>

Performs a type-checked assignment of a reflected value to this value.

fn reflect_ref(&self) -> ReflectRef<'_>

Returns an enumeration of “kinds” of type.

fn reflect_mut(&mut self) -> ReflectMut<'_>

Returns a mutable enumeration of “kinds” of type.

fn reflect_owned(self: Box<Entity>) -> ReflectOwned

Returns an owned enumeration of “kinds” of type.

fn reflect_hash(&self) -> Option<u64>

Returns a hash of the value (which includes the type).

fn reflect_partial_eq(&self, value: &(dyn Reflect + 'static)) -> Option<bool>

Returns a “partial equality” comparison result.

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

Debug formatter for the value.

fn serializable(&self) -> Option<Serializable<'_>>

Returns a serializable version of the value.

impl Serialize for Entity

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl SparseSetIndex for Entity

fn sparse_set_index(&self) -> usize

fn get_sparse_set_index(value: usize) -> Entity

impl Typed for Entity

fn type_info() -> &'static TypeInfo

Returns the compile-time info for the underlying type.

impl WorldQuery for Entity

SAFETY: no component or archetype access

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. 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.

const IS_ARCHETYPAL: bool = true

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

type Fetch<'w> = ()

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

type Item<'w> = Entity

The item returned by this WorldQuery

type ReadOnly = Entity

The read-only variant of this WorldQuery, which satisfies the ReadOnlyWorldQuery trait.

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<'wlong, 'wshort>( item: <Entity as WorldQuery>::Item<'wlong>, ) -> <Entity as WorldQuery>::Item<'wshort>

where 'wlong: 'wshort,

This function manually implements subtyping for the query items.

unsafe fn init_fetch<'w>( _world: &'w World, _state: &<Entity as WorldQuery>::State, _last_change_tick: u32, _change_tick: u32, ) -> <Entity as WorldQuery>::Fetch<'w>

Creates a new instance of this fetch.

unsafe fn clone_fetch<'w>( _fetch: &<Entity as WorldQuery>::Fetch<'w>, ) -> <Entity as WorldQuery>::Fetch<'w>

While this function can be called for any query, it is always safe to call if Self: ReadOnlyWorldQuery holds.

unsafe fn set_archetype<'w>( _fetch: &mut <Entity as WorldQuery>::Fetch<'w>, _state: &<Entity as WorldQuery>::State, _archetype: &'w Archetype, _table: &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 <Entity as WorldQuery>::Fetch<'w>, _state: &<Entity as WorldQuery>::State, _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 <Entity as WorldQuery>::Fetch<'w>, entity: Entity, _table_row: usize, ) -> <Entity 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( _state: &<Entity as WorldQuery>::State, _access: &mut FilteredAccess<ComponentId>, )

fn update_archetype_component_access( _state: &<Entity as WorldQuery>::State, _archetype: &Archetype, _access: &mut Access<ArchetypeComponentId>, )

fn init_state(_world: &mut World)

fn matches_component_set( _state: &<Entity as WorldQuery>::State, _set_contains_id: &impl Fn(ComponentId) -> bool, ) -> bool

unsafe fn filter_fetch( fetch: &mut Self::Fetch<'_>, entity: Entity, table_row: usize, ) -> bool

Safety

impl Copy for Entity

impl Eq for Entity

impl ReadOnlyWorldQuery for Entity

SAFETY: access is read only

impl StructuralPartialEq for Entity