Struct Entity

#[repr(C, align(8))]
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.

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.

Stability warning

For all intents and purposes, Entity should be treated as an opaque identifier. The internal bit representation is liable to change from release to release as are the behaviors or performance characteristics of any of its trait implementations (i.e. Ord, Hash, etc.). This means that changes in Entity’s representation, though made readable through various functions on the type, are not considered breaking changes under SemVer.

In particular, directly serializing with Serialize and Deserialize make zero guarantee of long term wire format compatibility. Changes in behavior will cause serialized Entity values persisted to long term storage (i.e. disk, databases, etc.) will fail to deserialize upon being updated.

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

impl Entity

pub const PLACEHOLDER: Self = _

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,
        }
    }
}

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.

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) -> Self

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.

pub const fn try_from_bits(bits: u64) -> Result<Self, 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.

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 copy 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

Formats the value using the given formatter.

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

Available on crate feature serialize only.

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for Entity

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

Formats the value using the given formatter.

impl From<Entity> for Identifier

fn from(value: Entity) -> Self

Converts to this type from the input type.

impl From<RemovedComponentEntity> for Entity

fn from(value: RemovedComponentEntity) -> Self

Converts to this type from the input type.

impl FromReflect for Entity

where Self: Any + Send + Sync,

fn from_reflect(reflect: &dyn Reflect) -> Option<Self>

Constructs a concrete instance of Self from a reflected value.

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.

impl GetTypeRegistration for Entity

where Self: Any + Send + Sync,

fn get_type_registration() -> TypeRegistration

Returns the default TypeRegistration for this type.

fn register_type_dependencies(registry: &mut TypeRegistry)

Registers other types needed by this type.

impl Hash for Entity

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

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: &Self) -> 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: &Self) -> 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 QueryData for Entity

SAFETY: Self is the same as Self::ReadOnly

type ReadOnly = Entity

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

impl Reflect for Entity

where Self: Any + Send + Sync,

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

Returns the TypeInfo of the type represented by this value.

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

Returns the value as a Box<dyn Any>.

fn as_any(&self) -> &dyn Any

Returns the value as a &dyn Any.

fn as_any_mut(&mut self) -> &mut dyn Any

Returns the value as a &mut dyn Any.

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

Casts this type to a boxed reflected value.

fn as_reflect(&self) -> &dyn Reflect

Casts this type to a reflected value.

fn as_reflect_mut(&mut self) -> &mut dyn Reflect

Casts this type to a mutable reflected value.

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

Clones the value as a Reflect trait object.

fn try_apply(&mut self, value: &dyn Reflect) -> Result<(), ApplyError>

Tries to apply 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_kind(&self) -> ReflectKind

Returns a zero-sized enumeration of “kinds” of type.

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

Returns an immutable enumeration of “kinds” of type.

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

Returns a mutable enumeration of “kinds” of type.

fn reflect_owned(self: Box<Self>) -> 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) -> Option<bool>

Returns a “partial equality” comparison result.

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

Applies a reflected value to this value.

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.

fn is_dynamic(&self) -> bool

Indicates whether or not this type is a dynamic type.

impl Serialize for Entity

Available on crate feature serialize only.

fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>

where S: Serializer,

Serialize this value into the given Serde serializer.

impl SparseSetIndex for Entity

fn sparse_set_index(&self) -> usize

Gets the sparse set index corresponding to this instance.

fn get_sparse_set_index(value: usize) -> Self

Creates a new instance of this type with the specified index.

impl TriggerTargets for Entity

fn components(&self) -> impl ExactSizeIterator<Item = ComponentId>

The components the trigger should target.

fn entities(&self) -> impl ExactSizeIterator<Item = Entity>

The entities the trigger should target.

impl TryFrom<Identifier> for Entity

type Error = IdentifierError

The type returned in the event of a conversion error.

fn try_from(value: Identifier) -> Result<Self, Self::Error>

Performs the conversion.

impl TypePath for Entity

where Self: Any + Send + Sync,

fn type_path() -> &'static str

Returns the fully qualified path of the underlying type.

fn short_type_path() -> &'static str

Returns a short, pretty-print enabled path to the type.

fn type_ident() -> Option<&'static str>

Returns the name of the type, or None if it is anonymous.

fn crate_name() -> Option<&'static str>

Returns the name of the crate the type is in, or None if it is anonymous.

fn module_path() -> Option<&'static str>

Returns the path to the module the type is in, or None if it is anonymous.

impl Typed for Entity

where Self: Any + Send + Sync,

fn type_info() -> &'static TypeInfo

Returns the compile-time info for the underlying type.

impl WorldQuery for Entity

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

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.

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.

type Fetch<'w> = ()

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

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

This function manually implements subtyping for the query items.

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 this fetch.

unsafe fn set_archetype<'w>( _fetch: &mut Self::Fetch<'w>, _state: &Self::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 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.

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 a entity in the current archetype.

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)

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: &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 Copy for Entity

impl Eq for Entity

impl ReadOnlyQueryData for Entity

SAFETY: access is read only