Struct hassium::prelude::World

pub struct World {
    pub res: Resources,
}

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.

Examples

use specs::prelude::*;

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_storage` returns a component storage.
    let pos_storage = world.read_storage::<Pos>();
    let vel_storage = world.read_storage::<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_storage::<Pos>();
    let vel_storage = world.read_storage::<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>(&mut self) where
    T: Component,
    <T as Component>::Storage: Default, 

Registers a new component, adding the component storage.

Calls register_with_storage with Default::default().

Does nothing if the component was already registered.

Examples

use specs::prelude::*;

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_storage<F, T>(&mut self, storage: F) where
    F: FnOnce() -> <T as Component>::Storage,
    T: Component, 

Registers a new component with a given storage.

Does nothing if the component was already registered.

pub fn system_data<'a, T>(&'a self) -> T where
    T: SystemData<'a>, 

Gets SystemData T from the World.

Examples

let mut world = World::new();
world.register::<Pos>();
world.register::<Vel>();
let storages: (WriteStorage<Pos>, ReadStorage<Vel>) = world.system_data();

Panics

• Panics if T is already borrowed in an incompatible way.

pub fn setup<'a, T>(&mut self) where
    T: SystemData<'a>, 

Sets up system data T for fetching afterwards.

pub fn exec<'a, F, R, T>(&'a mut self, f: F) -> R where
    F: FnOnce(T) -> R,
    T: SystemData<'a>, 

Executes f once, right now with the specified system data.

This sets up the system data f expects, fetches it and then executes f. You can see this like a system that only runs once.

This is especially useful if you either need a lot of system data or you want to build an entity and for that you need to access resources first

• just fetching the resources and building the entity would cause a double borrow.

Calling this method is equivalent to:

{ // note the extra scope
    world.setup::<MySystemData>();
    let my_data: MySystemData = world.system_data();
    my_data.do_something();
}

Examples

let mut world = World::new();

struct MyComp;

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

#[derive(Default)]
struct MyRes {
    field: i32,
}

world.exec(|(mut my_res,): (Write<MyRes>,)| {
    assert_eq!(my_res.field, 0);
    my_res.field = 5;
});

assert_eq!(world.read_resource::<MyRes>().field, 5);

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

Adds a resource to the world.

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::prelude::*;

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

pub fn read_storage<T>(&self) -> Storage<T, Fetch<MaskedStorage<T>>> where
    T: Component, 

Fetches a component's storage for reading.

Panics

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

pub fn write_storage<T>(&self) -> Storage<T, FetchMut<MaskedStorage<T>>> where
    T: Component, 

Fetches a component's storage for writing.

Panics

Panics if it is already borrowed (either immutably or mutably). Panics if the component has not been registered.

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

Fetches a resource for reading.

Panics

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

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

Fetches a resource for writing.

Panics

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

pub fn entities(&self) -> Read<EntitiesRes, DefaultProvider>

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.

Important traits for CreateIter<'a>

impl<'a> Iterator for CreateIter<'a> type Item = 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::prelude::*;

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.

Trait Implementations

impl Sync for World

impl Component for World

type Storage = DenseVecStorage<World>

Associated storage type for this component.

impl Send for World

impl Default for World

fn default() -> World

Returns the "default value" for a type.

impl Borrow<Resources> for World

fn borrow(&self) -> &Resources

Immutably borrows from an owned value.