#[repr(C, align(8))]
pub struct Entity { /* private fields */ }
Expand description

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.

These identifiers are only valid on the World it’s sourced from. Attempting to use an Entity to fetch entity components or metadata from a different world will either fail or return unexpected results.

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 EntityWorldMut::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 `EntityWorldMut`.
    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§

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impl Entity

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pub const PLACEHOLDER: Entity = _

An entity ID with a placeholder value. This may or may not correspond to an actual entity, and should be overwritten by a new value before being used.

Examples

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

// Create a new array of size 10 filled with invalid entity ids.
let mut entities: [Entity; 10] = [Entity::PLACEHOLDER; 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::PLACEHOLDER,
        }
    }
}
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pub const fn from_raw(index: u32) -> Entity

Creates a new entity ID with the specified index and a generation of 1.

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.

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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.

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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.

Panics

This method will likely panic if given u64 values that did not come from Entity::to_bits.

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pub const fn try_from_bits(bits: u64) -> Result<Entity, IdentifierError>

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.

This method is the fallible counterpart to Entity::from_bits.

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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.

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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§

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impl Clone for Entity

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fn clone(&self) -> Entity

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for Entity

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

Formats the value using the given formatter. Read more
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impl<'de> Deserialize<'de> for Entity

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fn deserialize<D>( deserializer: D ) -> Result<Entity, <D as Deserializer<'de>>::Error>
where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer. Read more
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impl From<Entity> for Identifier

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fn from(value: Entity) -> Identifier

Converts to this type from the input type.
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impl From<Entity> for SlotValue

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fn from(value: Entity) -> SlotValue

Converts to this type from the input type.
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impl From<RemovedComponentEntity> for Entity

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fn from(value: RemovedComponentEntity) -> Entity

Converts to this type from the input type.
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impl FromReflect for Entity
where Entity: Any + Send + Sync,

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

Constructs a concrete instance of Self from a reflected value.
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fn take_from_reflect( reflect: Box<dyn Reflect> ) -> Result<Self, Box<dyn Reflect>>

Attempts to downcast the given value to Self using, constructing the value using from_reflect if that fails. Read more
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impl GetTypeRegistration for Entity
where Entity: Any + Send + Sync,

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impl Hash for Entity

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fn hash<H>(&self, state: &mut H)
where H: Hasher,

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl Ord for Entity

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

This method returns an Ordering between self and other. Read more
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fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
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fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
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fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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impl PartialEq for Entity

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

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl PartialOrd for Entity

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

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl QueryData for Entity

SAFETY: Self is the same as Self::ReadOnly

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type ReadOnly = Entity

The read-only variant of this QueryData, which satisfies the ReadOnlyQueryData trait.
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impl Reflect for Entity
where Entity: Any + Send + Sync,

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fn get_represented_type_info(&self) -> Option<&'static TypeInfo>

Returns the TypeInfo of the type represented by this value. Read more
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fn into_any(self: Box<Entity>) -> Box<dyn Any>

Returns the value as a Box<dyn Any>.
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fn as_any(&self) -> &(dyn Any + 'static)

Returns the value as a &dyn Any.
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fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)

Returns the value as a &mut dyn Any.
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fn into_reflect(self: Box<Entity>) -> Box<dyn Reflect>

Casts this type to a boxed reflected value.
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fn as_reflect(&self) -> &(dyn Reflect + 'static)

Casts this type to a reflected value.
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fn as_reflect_mut(&mut self) -> &mut (dyn Reflect + 'static)

Casts this type to a mutable reflected value.
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fn clone_value(&self) -> Box<dyn Reflect>

Clones the value as a Reflect trait object. Read more
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fn apply(&mut self, value: &(dyn Reflect + 'static))

Applies a reflected value to this value. Read more
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fn set(&mut self, value: Box<dyn Reflect>) -> Result<(), Box<dyn Reflect>>

Performs a type-checked assignment of a reflected value to this value. Read more
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fn reflect_kind(&self) -> ReflectKind

Returns a zero-sized enumeration of “kinds” of type. Read more
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fn reflect_ref(&self) -> ReflectRef<'_>

Returns an immutable enumeration of “kinds” of type. Read more
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fn reflect_mut(&mut self) -> ReflectMut<'_>

Returns a mutable enumeration of “kinds” of type. Read more
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fn reflect_owned(self: Box<Entity>) -> ReflectOwned

Returns an owned enumeration of “kinds” of type. Read more
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fn reflect_hash(&self) -> Option<u64>

Returns a hash of the value (which includes the type). Read more
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fn reflect_partial_eq(&self, value: &(dyn Reflect + 'static)) -> Option<bool>

Returns a “partial equality” comparison result. Read more
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fn debug(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Debug formatter for the value. Read more
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fn serializable(&self) -> Option<Serializable<'_>>

Returns a serializable version of the value. Read more
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fn is_dynamic(&self) -> bool

Indicates whether or not this type is a dynamic type. Read more
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impl Serialize for Entity

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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. Read more
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impl SparseSetIndex for Entity

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fn sparse_set_index(&self) -> usize

Gets the sparse set index corresponding to this instance.
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fn get_sparse_set_index(value: usize) -> Entity

Creates a new instance of this type with the specified index.
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impl TryFrom<Identifier> for Entity

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type Error = IdentifierError

The type returned in the event of a conversion error.
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fn try_from( value: Identifier ) -> Result<Entity, <Entity as TryFrom<Identifier>>::Error>

Performs the conversion.
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impl TypePath for Entity
where Entity: Any + Send + Sync,

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fn type_path() -> &'static str

Returns the fully qualified path of the underlying type. Read more
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fn short_type_path() -> &'static str

Returns a short, pretty-print enabled path to the type. Read more
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fn type_ident() -> Option<&'static str>

Returns the name of the type, or None if it is anonymous. Read more
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fn crate_name() -> Option<&'static str>

Returns the name of the crate the type is in, or None if it is anonymous. Read more
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fn module_path() -> Option<&'static str>

Returns the path to the module the type is in, or None if it is anonymous. Read more
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impl Typed for Entity
where Entity: Any + Send + Sync,

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fn type_info() -> &'static TypeInfo

Returns the compile-time info for the underlying type.
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impl WorldQuery for Entity

SAFETY: update_component_access and update_archetype_component_access do nothing. This is sound because fetch does not access components.

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type Item<'w> = Entity

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.
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type Fetch<'w> = ()

Per archetype/table state used by this WorldQuery to fetch Self::Item
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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.
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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.
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unsafe fn init_fetch<'w>( _world: UnsafeWorldCell<'w>, _state: &<Entity as WorldQuery>::State, _last_run: Tick, _this_run: Tick ) -> <Entity as WorldQuery>::Fetch<'w>

Creates a new instance of this fetch. Read more
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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.
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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. Read more
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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. Read more
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unsafe fn fetch<'w>( _fetch: &mut <Entity as WorldQuery>::Fetch<'w>, entity: Entity, _table_row: TableRow ) -> <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. Read more
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fn update_component_access( _state: &<Entity as WorldQuery>::State, _access: &mut FilteredAccess<ComponentId> )

Adds any component accesses used by this WorldQuery to access.
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fn init_state(_world: &mut World)

Creates and initializes a State for this WorldQuery type.
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fn get_state(_world: &World) -> Option<()>

Attempts to initializes a State for this WorldQuery type.
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fn matches_component_set( _state: &<Entity as WorldQuery>::State, _set_contains_id: &impl Fn(ComponentId) -> bool ) -> bool

Returns true if this query matches a set of components. Otherwise, returns false.
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fn set_access(_state: &mut Self::State, _access: &FilteredAccess<ComponentId>)

Sets available accesses for implementors with dynamic access such as FilteredEntityRef or FilteredEntityMut. Read more
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impl Copy for Entity

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impl Eq for Entity

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impl ReadOnlyQueryData for Entity

SAFETY: access is read only

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impl<T> Any for T
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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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fn as_bind_group_shader_type(&self, _images: &RenderAssets<Image>) -> U

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fn compare(&self, key: &K) -> Ordering

Compare self to key and return their ordering.
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impl<T> Downcast for T
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Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s.
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fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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