Struct hecs::World

pub struct World { /* private fields */ }

An unordered collection of entities, each having any number of distinctly typed components

Similar to HashMap<Entity, Vec<Box<dyn Any>>> where each Vec never contains two of the same type, but far more efficient to traverse.

The components of entities who have the same set of component types are stored in contiguous runs, allowing for extremely fast, cache-friendly iteration.

There is a maximum number of unique entity IDs, which means that there is a maximum number of live entities. When old entities are despawned, their IDs will be reused on a future entity, and old Entity values with that ID will be invalidated.

Collisions

If an entity is despawned and its Entity handle is preserved over the course of billions of following spawns and despawns, that handle may, in rare circumstances, collide with a newly-allocated Entity handle. Very long-lived applications should therefore limit the period over which they may retain handles of despawned entities.

Implementations

impl World

pub fn new() -> Self

Create an empty world

pub fn spawn(&mut self, components: impl DynamicBundle) -> Entity

Create an entity with certain components

Returns the ID of the newly created entity.

Arguments can be tuples, structs annotated with #[derive(Bundle)], or the result of calling build on an EntityBuilder, which is useful if the set of components isn’t statically known. To spawn an entity with only one component, use a one-element tuple like (x,).

Any type that satisfies Send + Sync + 'static can be used as a component.

Example

let mut world = World::new();
let a = world.spawn((123, "abc"));
let b = world.spawn((456, true));

pub fn spawn_at(&mut self, handle: Entity, components: impl DynamicBundle)

Create an entity with certain components and a specific Entity handle.

See spawn.

Despawns any existing entity with the same Entity::id.

Useful for easy handle-preserving deserialization. Be cautious resurrecting old Entity handles in already-populated worlds as it vastly increases the likelihood of collisions.

Example

let mut world = World::new();
let a = world.spawn((123, "abc"));
let b = world.spawn((456, true));
world.despawn(a);
assert!(!world.contains(a));
// all previous Entity values pointing to 'a' will be live again, instead pointing to the new entity.
world.spawn_at(a, (789, "ABC"));
assert!(world.contains(a));

pub fn spawn_batch<I>(&mut self, iter: I) -> SpawnBatchIter<'_, I::IntoIter>

where I: IntoIterator, I::Item: Bundle + 'static,

Efficiently spawn a large number of entities with the same statically-typed components

Faster than calling spawn repeatedly with the same components, but requires that component types are known at compile time.

Example

let mut world = World::new();
let entities = world.spawn_batch((0..1_000).map(|i| (i, "abc"))).collect::<Vec<_>>();
for i in 0..1_000 {
    assert_eq!(*world.get::<&i32>(entities[i]).unwrap(), i as i32);
}

pub fn spawn_column_batch( &mut self, batch: ColumnBatch ) -> SpawnColumnBatchIter<'_>

Super-efficiently spawn the contents of a ColumnBatch

The fastest, but most specialized, way to spawn large numbers of entities. Useful for high performance deserialization. Supports dynamic component types.

pub fn spawn_column_batch_at(&mut self, handles: &[Entity], batch: ColumnBatch)

Hybrid of spawn_column_batch and spawn_at

pub fn reserve_entities(&self, count: u32) -> ReserveEntitiesIterator<'_>

Allocate many entities ID concurrently

Unlike spawn, this can be called concurrently with other operations on the World such as queries, but does not immediately create the entities. Reserved entities are not visible to queries or world iteration, but can be otherwise operated on freely. Operations that add or remove components or entities, such as insert or despawn, will cause all outstanding reserved entities to become real entities before proceeding. This can also be done explicitly by calling flush.

Useful for reserving an ID that will later have components attached to it with insert.

pub fn reserve_entity(&self) -> Entity

Allocate an entity ID concurrently

See reserve_entities.

pub fn despawn(&mut self, entity: Entity) -> Result<(), NoSuchEntity>

Destroy an entity and all its components

See also take.

pub fn reserve<T: Bundle + 'static>(&mut self, additional: u32)

Ensure at least additional entities with exact components T can be spawned without reallocating

pub fn clear(&mut self)

Despawn all entities

Preserves allocated storage for reuse but clears metadata so that Entity values will repeat (in contrast to despawn).

pub fn contains(&self, entity: Entity) -> bool

Whether entity still exists

pub fn query<Q: Query>(&self) -> QueryBorrow<'_, Q>

Efficiently iterate over all entities that have certain components, using dynamic borrow checking

Prefer query_mut when concurrent access to the World is not required.

Calling iter on the returned value yields (Entity, Q) tuples, where Q is some query type. A query type is any type for which an implementation of Query exists, e.g. &T, &mut T, a tuple of query types, or an Option wrapping a query type, where T is any component type. Components queried with &mut must only appear once. Entities which do not have a component type referenced outside of an Option will be skipped.

Entities are yielded in arbitrary order.

The returned QueryBorrow can be further transformed with combinator methods; see its documentation for details.

Iterating a query will panic if it would violate an existing unique reference or construct an invalid unique reference. This occurs when two simultaneously-active queries could expose the same entity. Simultaneous queries can access the same component type if and only if the world contains no entities that have all components required by both queries, assuming no other component borrows are outstanding.

Iterating a query yields references with lifetimes bound to the QueryBorrow returned here. To ensure those are invalidated, the return value of this method must be dropped for its dynamic borrows from the world to be released. Similarly, lifetime rules ensure that references obtained from a query cannot outlive the QueryBorrow.

Example

let mut world = World::new();
let a = world.spawn((123, true, "abc"));
let b = world.spawn((456, false));
let c = world.spawn((42, "def"));
let entities = world.query::<(&i32, &bool)>()
    .iter()
    .map(|(e, (&i, &b))| (e, i, b)) // Copy out of the world
    .collect::<Vec<_>>();
assert_eq!(entities.len(), 2);
assert!(entities.contains(&(a, 123, true)));
assert!(entities.contains(&(b, 456, false)));

pub fn query_mut<Q: Query>(&mut self) -> QueryMut<'_, Q>

Query a uniquely borrowed world

Like query, but faster because dynamic borrow checks can be skipped. Note that, unlike query, this returns an IntoIterator which can be passed directly to a for loop.

pub fn query_one<Q: Query>( &self, entity: Entity ) -> Result<QueryOne<'_, Q>, NoSuchEntity>

Prepare a query against a single entity, using dynamic borrow checking

Prefer query_one_mut when concurrent access to the World is not required.

Call get on the resulting QueryOne to actually execute the query. The QueryOne value is responsible for releasing the dynamically-checked borrow made by get, so it can’t be dropped while references returned by get are live.

Handy for accessing multiple components simultaneously.

Example

let mut world = World::new();
let a = world.spawn((123, true, "abc"));
// The returned query must outlive the borrow made by `get`
let mut query = world.query_one::<(&mut i32, &bool)>(a).unwrap();
let (number, flag) = query.get().unwrap();
if *flag { *number *= 2; }
assert_eq!(*number, 246);

pub fn query_one_mut<Q: Query>( &mut self, entity: Entity ) -> Result<Q::Item<'_>, QueryOneError>

Query a single entity in a uniquely borrow world

Like query_one, but faster because dynamic borrow checks can be skipped. Note that, unlike query_one, on success this returns the query’s results directly.

pub fn get<'a, T: ComponentRef<'a>>( &'a self, entity: Entity ) -> Result<T::Ref, ComponentError>

Short-hand for entity followed by EntityRef::get

pub fn satisfies<Q: Query>(&self, entity: Entity) -> Result<bool, NoSuchEntity>

Short-hand for entity followed by EntityRef::satisfies

pub fn entity(&self, entity: Entity) -> Result<EntityRef<'_>, NoSuchEntity>

Access an entity regardless of its component types

Does not immediately borrow any component.

pub unsafe fn find_entity_from_id(&self, id: u32) -> Entity

Given an id obtained from Entity::id, reconstruct the still-live Entity.

Safety

id must correspond to a currently live Entity. A despawned or never-allocated id will produce undefined behavior.

pub fn iter(&self) -> Iter<'_>

Iterate over all entities in the world

Entities are yielded in arbitrary order. Prefer query for better performance when components will be accessed in predictable patterns.

Example

let mut world = World::new();
let a = world.spawn(());
let b = world.spawn(());
let ids = world.iter().map(|entity_ref| entity_ref.entity()).collect::<Vec<_>>();
assert_eq!(ids.len(), 2);
assert!(ids.contains(&a));
assert!(ids.contains(&b));

pub fn insert( &mut self, entity: Entity, components: impl DynamicBundle ) -> Result<(), NoSuchEntity>

Add components to entity

Computational cost is proportional to the number of components entity has. If an entity already has a component of a certain type, it is dropped and replaced.

When inserting a single component, see insert_one for convenience.

Example

let mut world = World::new();
let e = world.spawn((123, "abc"));
world.insert(e, (456, true));
assert_eq!(*world.get::<&i32>(e).unwrap(), 456);
assert_eq!(*world.get::<&bool>(e).unwrap(), true);

pub fn insert_one( &mut self, entity: Entity, component: impl Component ) -> Result<(), NoSuchEntity>

Add component to entity

See insert.

pub fn remove<T: Bundle + 'static>( &mut self, entity: Entity ) -> Result<T, ComponentError>

Remove components from entity

Computational cost is proportional to the number of components entity has. The entity itself is not removed, even if no components remain; use despawn for that. If any component in T is not present in entity, no components are removed and an error is returned.

When removing a single component, see remove_one for convenience.

Example

let mut world = World::new();
let e = world.spawn((123, "abc", true));
assert_eq!(world.remove::<(i32, &str)>(e), Ok((123, "abc")));
assert!(world.get::<&i32>(e).is_err());
assert!(world.get::<&&str>(e).is_err());
assert_eq!(*world.get::<&bool>(e).unwrap(), true);

pub fn remove_one<T: Component>( &mut self, entity: Entity ) -> Result<T, ComponentError>

Remove the T component from entity

See remove.

pub fn exchange<S: Bundle + 'static, T: DynamicBundle>( &mut self, entity: Entity, components: T ) -> Result<S, ComponentError>

Remove S components from entity and then add components

This has the same effect as calling remove::<S> and then insert::<T>, but is more efficient as the intermediate archetype after removal but before insertion is skipped.

pub fn exchange_one<S: Component, T: Component>( &mut self, entity: Entity, component: T ) -> Result<S, ComponentError>

Remove the S component from entity and then add component

See exchange.

pub unsafe fn get_unchecked<'a, T: ComponentRef<'a>>( &'a self, entity: Entity ) -> Result<T, ComponentError>

Borrow a single component of entity without safety checks

T must be a shared or unique reference to a component type.

Should only be used as a building block for safe abstractions.

Safety

entity must have been previously obtained from this World, and no unique borrow of the same component of entity may be live simultaneous to the returned reference.

pub fn flush(&mut self)

Convert all reserved entities into empty entities that can be iterated and accessed

Invoked implicitly by operations that add or remove components or entities, i.e. all variations of spawn, despawn, insert, and remove.

pub fn archetypes(&self) -> impl ExactSizeIterator<Item = &Archetype> + '_

Inspect the archetypes that entities are organized into

Useful for dynamically scheduling concurrent queries by checking borrows in advance, and for efficient serialization.

pub fn take(&mut self, entity: Entity) -> Result<TakenEntity<'_>, NoSuchEntity>

Despawn entity, yielding a DynamicBundle of its components

Useful for moving entities between worlds.

pub fn archetypes_generation(&self) -> ArchetypesGeneration

Returns a distinct value after archetypes is changed

Store the current value after deriving information from archetypes, then check whether the value returned by this function differs before attempting an operation that relies on its correctness. Useful for determining whether e.g. a concurrent query execution plan is still correct.

The generation may be, but is not necessarily, changed as a result of adding or removing any entity or component.

Example

let mut world = World::new();
let initial_gen = world.archetypes_generation();
world.spawn((123, "abc"));
assert_ne!(initial_gen, world.archetypes_generation());

pub fn len(&self) -> u32

Number of currently live entities

pub fn is_empty(&self) -> bool

Whether no entities are live

Trait Implementations

impl Default for World

fn default() -> Self

Returns the “default value” for a type.

impl<A: DynamicBundle> Extend<A> for World

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = A>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<A: DynamicBundle> FromIterator<A> for World

fn from_iter<I: IntoIterator<Item = A>>(iter: I) -> Self

Creates a value from an iterator.

impl<'a> IntoIterator for &'a World

type IntoIter = Iter<'a>

Which kind of iterator are we turning this into?

type Item = EntityRef<'a>

The type of the elements being iterated over.

fn into_iter(self) -> Iter<'a>

Creates an iterator from a value.

impl Send for World

impl Sync for World