Struct specs::World

pub struct World {
    pub res: Resources,
    // some fields omitted
}

The World struct contains the component storages and other resources.

Many methods take &self which works because everything is stored with interior mutability. In case you violate the borrowing rules of Rust (multiple reads xor one write), you will get a panic.

Component / Resources ids

Components and resources may, in addition to their type, be identified by an id of type usize. The convenience methods dealing with components assume that it's 0.

If a system attempts to access a component/resource that has not been registered/added, it will panic when run. Add all components with World::register before running any systems. Also add all resources with World::add_resource.

Examples

use specs::World;

let mut world = World::new();
world.register::<Pos>();
world.register::<Vel>();

world.add_resource(DeltaTime(0.02));

world
    .create_entity()
    .with(Pos { x: 1.0, y: 2.0 })
    .with(Vel { x: -1.0, y: 0.0 })
    .build();

let b = world
    .create_entity()
    .with(Pos { x: 3.0, y: 5.0 })
    .with(Vel { x: 1.0, y: 0.0 })
    .build();

let c = world
    .create_entity()
    .with(Pos { x: 0.0, y: 1.0 })
    .with(Vel { x: 0.0, y: 1.0 })
    .build();

{
    // `World::read` returns a component storage.
    let pos_storage = world.read::<Pos>();
    let vel_storage = world.read::<Vel>();

    // `Storage::get` allows to get a component from it:
    assert_eq!(pos_storage.get(b), Some(&Pos { x: 3.0, y: 5.0 }));
    assert_eq!(vel_storage.get(c), Some(&Vel { x: 0.0, y: 1.0 }));
}

let empty = world.create_entity().build();

{
    // This time, we write to the `Pos` storage:
    let mut pos_storage = world.write::<Pos>();
    let vel_storage = world.read::<Vel>();

    assert!(pos_storage.get(empty).is_none());

    // You can also insert components after creating the entity:
    pos_storage.insert(empty, Pos { x: 3.1, y: 4.15 });

    assert!(pos_storage.get(empty).is_some());
}

Fields

res: Resources

The resources used for this world.

Methods

impl World

pub fn new() -> World

Creates a new empty World.

pub fn register<T: Component>(&mut self)

Registers a new component.

Calls register_with_id with id 0, which is the default for component ids.

Does nothing if the component was already registered.

Examples

use specs::{Component, DenseVecStorage, World};

struct Pos {
    x: f32,
    y: f32,
}

impl Component for Pos {
    type Storage = DenseVecStorage<Self>;
}

let mut world = World::new();
world.register::<Pos>();
// Register all other components like this

pub fn register_with_id<T: Component>(&mut self, id: usize)

Registers a new component with a given id.

Does nothing if the component was already registered.

pub fn add_resource<T: Resource>(&mut self, res: T)

Adds a resource with the default ID (0).

If the resource already exists it will be overwritten.

Difference between resources and components

While components exist per entity, resources are like globals in the World. Components are stored in component storages, which are resources themselves.

Everything that is Any + Send + Sync can be a resource.

Built-in resources

There are two built-in resources:

• LazyUpdate and
• EntitiesRes

Both of them should only be fetched immutably, which is why the latter one has a type def for convenience: Entities which is just Fetch<EntitiesRes>. Both resources are special and need to execute code at the end of the frame, which is done in World::maintain.

Examples

use specs::World;

let mut world = World::new();
world.add_resource(timer);
world.add_resource(server_con);

pub fn add_resource_with_id<T: Resource>(&mut self, res: T, id: usize)

Adds a resource with a given ID.

If the resource already exists it will be overwritten.

pub fn read<T: Component>(&self) -> ReadStorage<T>

Fetches a component's storage with the default id for reading.

Convenience method for read_with_id, using the default component id (0).

Panics

Panics if it is already borrowed mutably. Panics if the component has not been registered.

pub fn write<T: Component>(&self) -> WriteStorage<T>

Fetches a component's storage with the default id for writing.

Convenience method for write_with_id, using the default component id (0).

Panics

Panics if it is already borrowed. Panics if the component has not been registered.

pub fn read_with_id<T: Component>(&self, id: usize) -> ReadStorage<T>

Fetches a component's storage with a specified component id for reading. ID is for components registered with an ID, and does not correspond to entity IDs. For basic setups, use an ID of 0 or use the read() function.

Panics

Panics if it is already borrowed mutably. Also panics if the component is not registered with World::register.

pub fn write_with_id<T: Component>(&self, id: usize) -> WriteStorage<T>

Fetches a component's storage with a specified id for writing. ID is for components registered with an ID, and does not correspond to entity IDs. For basic setups, use an ID of 0 or use the write() function.

Panics

Panics if it is already borrowed. Also panics if the component is not registered with World::register.

pub fn read_resource_with_id<T: Resource>(&self, id: usize) -> Fetch<T>

Fetches a resource with a specified id for reading. ID is for resources registered with an ID, and does not correspond to entity IDs. For basic setups, use an ID of 0 or use the read_resource() function.

Panics

Panics if it is already borrowed mutably. Panics if the resource has not been added.

pub fn write_resource_with_id<T: Resource>(&self, id: usize) -> FetchMut<T>

Fetches a resource with a specified id for writing. ID is for resources registered with an ID, and does not correspond to entity IDs. For basic setups, use an ID of 0 or use the write_resource() function.

Panics

Panics if it is already borrowed. Panics if the resource has not been added.

pub fn read_resource<T: Resource>(&self) -> Fetch<T>

Fetches a resource with the default id for reading.

Convenience method for read_resource_with_id, using the default component id (0).

Panics

Panics if it is already borrowed mutably. Panics if the resource has not been added.

pub fn write_resource<T: Resource>(&self) -> FetchMut<T>

Fetches a resource with the default id for writing.

Convenience method for write_resource_with_id, using the default component id (0).

Panics

Panics if it is already borrowed. Panics if the resource has not been added.

pub fn entities(&self) -> Fetch<EntitiesRes>

Convenience method for fetching entities.

Creation and deletion of entities with the Entities struct are atomically, so the actual changes will be applied with the next call to maintain().

pub fn create_entity(&mut self) -> EntityBuilder

Allows building an entity with its components.

This takes a mutable reference to the World, since no component storage this builder accesses may be borrowed. If it's necessary that you borrow a resource from the World while this builder is alive, you can use create_entity_unchecked.

pub fn create_entity_unchecked(&self) -> EntityBuilder

Allows building an entity with its components.

You have to make sure that no component storage is borrowed during the building!

This variant is only recommended if you need to borrow a resource during the entity building. If possible, try to use create_entity.

pub fn create_iter(&mut self) -> CreateIter

Returns an iterator for entity creation. This makes it easy to create a whole collection of them.

Examples

use specs::World;

let mut world = World::new();
let five_entities: Vec<_> = world.create_iter().take(5).collect();

pub fn delete_entity(&mut self, entity: Entity) -> Result<(), WrongGeneration>

Deletes an entity and its components.

pub fn delete_entities(
    &mut self,
    delete: &[Entity]
) -> Result<(), WrongGeneration>

Deletes the specified entities and their components.

pub fn delete_all(&mut self)

Deletes all entities and their components.

pub fn is_alive(&self, e: Entity) -> bool

Checks if an entity is alive. Please note that atomically created or deleted entities (the ones created / deleted with the Entities struct) are not handled by this method. Therefore, you should have called maintain() before using this method.

If you want to get this functionality before a maintain(), you are most likely in a system; from there, just access the Entities resource and call the is_alive method.

Panics

Panics if generation is dead.

pub fn maintain(&mut self)

Merges in the appendix, recording all the dynamically created and deleted entities into the persistent generations vector. Also removes all the abandoned components.

Additionally, LazyUpdate will be merged.

pub fn add_bundle<B>(&mut self, bundle: B) where
    B: Bundle, 

Adds the given bundle of resources/components.

Trait Implementations

impl Send for World

impl Sync for World

impl Borrow<Resources> for World

fn borrow(&self) -> &Resources

Immutably borrows from an owned value.

impl Component for World

type Storage = DenseVecStorage<Self>

Associated storage type for this component.

impl Default for World

fn default() -> Self

Returns the "default value" for a type.