Type Alias specs::storage::ReadStorage

pub type ReadStorage<'a, T> = Storage<'a, T, Fetch<'a, MaskedStorage<T>>>;

A storage with read access.

This is just a type alias for a fetched component storage.

The main functionality it provides is listed in the following, however make sure to also check out the documentation for the respective methods on Storage.

Aliasing

It is strictly disallowed to get both a ReadStorage and a WriteStorage of the same component. Because Specs uses interior mutability for its resources, we can’t check this at compile time. If you try to do this, you will get a panic.

It is explicitly allowed to get multiple ReadStorages for the same component.

Joining storages

&ReadStorage implements Join, which allows to do something like this:

use specs::prelude::*;

struct Pos;
impl Component for Pos {
    type Storage = VecStorage<Self>;
}
struct Vel;
impl Component for Vel {
    type Storage = VecStorage<Self>;
}

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

for (pos, vel) in (&pos_storage, &vel_storage).join() {}

This joins the position and the velocity storage, which means it only iterates over the components of entities that have both a position and a velocity.

Retrieving single components

If you have an entity (for example because you stored it before or because you’re joining over Entities), you can get a single component by calling Storage::get:

let entity1 = world.create_entity().with(Pos).build();
let entity2 = world.create_entity().with(Vel).build();

assert_eq!(pos_storage.get(entity1), Some(&Pos));
assert_eq!(pos_storage.get(entity2), None);

assert_eq!(vel_storage.get(entity1), None);
assert_eq!(vel_storage.get(entity2), Some(&Vel));

Usage as SystemData

ReadStorage implements SystemData which allows you to get it inside a system by simply adding it to the tuple:

#[derive(Debug)]
struct Pos {
    x: f32,
    y: f32,
}

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

struct Sys;

impl<'a> System<'a> for Sys {
    type SystemData = (Entities<'a>, ReadStorage<'a, Pos>);

    fn run(&mut self, (ent, pos): Self::SystemData) {
        for (ent, pos) in (&*ent, &pos).join() {
            println!("Entitiy with id {} has a position of {:?}", ent.id(), pos);
        }
    }
}

These operations can’t mutate anything; if you want to do insertions or modify components, you need to use WriteStorage. Note that you can also use LazyUpdate , which does insertions on World::maintain. This allows more concurrency and is designed to be used for entity initialization.

Aliased Type

struct ReadStorage<'a, T> { /* private fields */ }

Implementations

impl<'e, T, D> Storage<'e, T, D>where T: Component, D: DerefMut<Target = MaskedStorage<T>>,

pub fn entry<'a>( &'a mut self, e: Entity ) -> Result<StorageEntry<'a, 'e, T, D>, WrongGeneration>where 'e: 'a,

Returns an entry to the component associated to the entity.

Behaves somewhat similarly to std::collections::HashMap’s entry api.

Example

if let Ok(entry) = storage.entry(entity) {
    entry.or_insert(Comp { field: 55 });
}

pub fn entries<'a>(&'a mut self) -> Entries<'a, 'e, T, D>

Returns a LendJoin-able structure that yields all indices, returning StorageEntry for all elements

WARNING: Do not have a join of only Entriess. Otherwise the join will iterate over every single index of the bitset. If you want a join with all Entriess, add an EntitiesRes to the join as well to bound the join to all entities that are alive.

Example

let mut join = (counters.entries(), &marker).lend_join();
while let Some((mut counter, _)) = join.next() {
    let counter = counter.or_insert_with(Default::default);
    counter.increase();

    if counter.reached_limit() {
        counter.reset();
        // Do something
    }
}

pub fn entry_inner<'a>(&'a mut self, id: Index) -> StorageEntry<'a, 'e, T, D>

Returns an entry to the component associated with the provided index.

Does not check whether an entity is alive!

impl<T, D> Storage<'_, T, D>where T: Component, D: Deref<Target = MaskedStorage<T>>,

pub fn restrict<'rf>(&'rf self) -> RestrictedStorage<'rf, T, &T::Storage>

Builds an immutable RestrictedStorage out of a Storage. Allows deferred unchecked access to the entity’s component.

This is returned as a ParallelRestriction version since you can only get immutable components with this which is safe for parallel by default.

impl<T, D> Storage<'_, T, D>where T: Component, D: DerefMut<Target = MaskedStorage<T>>,

pub fn restrict_mut<'rf>( &'rf mut self ) -> RestrictedStorage<'rf, T, &mut T::Storage>

Builds a mutable RestrictedStorage out of a Storage. Allows restricted access to the inner components without allowing invalidating the bitset for iteration in Join.

impl<'e, T, D> Storage<'e, T, D>where T: Component, T::Storage: Tracked, D: Deref<Target = MaskedStorage<T>>,

pub fn channel(&self) -> &EventChannel<ComponentEvent>

Returns the event channel tracking modified components.

pub fn event_emission(&self) -> bool

Returns the actual state of the event emission.

impl<'e, T, D> Storage<'e, T, D>where T: Component, T::Storage: Tracked, D: DerefMut<Target = MaskedStorage<T>>,

pub fn channel_mut(&mut self) -> &mut EventChannel<ComponentEvent>

Returns the event channel for insertions/removals/modifications of this storage’s components.

pub fn register_reader(&mut self) -> ReaderId<ComponentEvent>

Starts tracking component events. Note that this reader id should be used every frame, otherwise events will pile up and memory use by the event channel will grow waiting for this reader.

pub fn flag(&mut self, event: ComponentEvent)

Flags an index with a ComponentEvent.

pub fn set_event_emission(&mut self, emit: bool)

Controls the events signal emission. When this is set to false the events modified/inserted/removed are not emitted.

impl<'e, T, D> Storage<'e, T, D>

pub fn new(entities: Fetch<'e, EntitiesRes>, data: D) -> Storage<'e, T, D>

Creates a new Storage from a fetched allocator and a immutable or mutable MaskedStorage, named data.

impl<'e, T, D> Storage<'e, T, D>where T: Component, D: Deref<Target = MaskedStorage<T>>,

pub fn unprotected_storage(&self) -> &T::Storage

Gets the wrapped storage.

pub fn fetched_entities(&self) -> &EntitiesRes

Returns the EntitiesRes resource fetched by this storage. This does not have anything to do with the components inside. You only want to use this when implementing additional methods for Storage via an extension trait.

pub fn get(&self, e: Entity) -> Option<&T>

Tries to read the data associated with an Entity.

pub fn count(&self) -> usize

Computes the number of elements this Storage contains by counting the bits in the bit set. This operation will never be performed in constant time.

pub fn is_empty(&self) -> bool

Checks whether this Storage is empty. This operation is very cheap.

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

Returns true if the storage has a component for this entity, and that entity is alive.

pub fn mask(&self) -> &BitSet

Returns a reference to the bitset of this storage which allows filtering by the component type without actually getting the component.

impl<'e, T, D> Storage<'e, T, D>where T: Component, D: Deref<Target = MaskedStorage<T>>, T::Storage: SliceAccess<T>,

pub fn as_slice(&self) -> &[<T::Storage as SliceAccess<T>>::Element]

Returns the component data as a slice.

The indices of this slice may not correspond to anything in particular. Check the underlying storage documentation for details.

impl<'e, T, D> Storage<'e, T, D>where T: Component, D: DerefMut<Target = MaskedStorage<T>>, T::Storage: SliceAccess<T>,

pub fn as_mut_slice(&mut self) -> &mut [<T::Storage as SliceAccess<T>>::Element]

Returns the component data as a slice.

The indices of this slice may not correspond to anything in particular. Check the underlying storage documentation for details.

impl<'e, T, D> Storage<'e, T, D>where T: Component, D: DerefMut<Target = MaskedStorage<T>>,

pub unsafe fn unprotected_storage_mut(&mut self) -> &mut T::Storage

Gets mutable access to the wrapped storage.

Safety

This is unsafe because modifying the wrapped storage without also updating the mask bitset accordingly can result in illegal memory access.

pub fn get_mut( &mut self, e: Entity ) -> Option<<<T as Component>::Storage as UnprotectedStorage<T>>::AccessMut<'_>>

Tries to mutate the data associated with an Entity.

pub fn insert(&mut self, e: Entity, v: T) -> InsertResult<T>

Inserts new data for a given Entity. Returns the result of the operation as a InsertResult<T>

If a component already existed for the given Entity, then it will be overwritten with the new component. If it did overwrite, then the result will contain Some(T) where T is the previous component.

pub fn remove(&mut self, e: Entity) -> Option<T>

Removes the data associated with an Entity.

pub fn clear(&mut self)

Clears the contents of the storage.

pub fn drain(&mut self) -> Drain<'_, T>

Creates a draining storage wrapper which can be .joined to get a draining iterator.

Trait Implementations

impl<'a, T, D: Clone> Clone for Storage<'a, T, D>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a: 'b, 'b, T> GenericReadStorage for &'b ReadStorage<'a, T>where T: Component,

type Component = T

The component type of the storage

fn get(&self, entity: Entity) -> Option<&Self::Component>

Get immutable access to an Entitys component

fn _private() -> Seal

Private function to seal the trait

impl<'a, T> GenericReadStorage for ReadStorage<'a, T>where T: Component,

type Component = T

The component type of the storage

fn get(&self, entity: Entity) -> Option<&Self::Component>

Get immutable access to an Entitys component

fn _private() -> Seal

Private function to seal the trait

impl<'a, T> SystemData<'a> for ReadStorage<'a, T>where T: Component,

fn setup(res: &mut World)

Sets up the system data for fetching it from the World.

fn fetch(res: &'a World) -> Self

Fetches the system data from World. Note that this is only specified for one concrete lifetime 'a, you need to implement the SystemData trait for every possible lifetime.

fn reads() -> Vec<ResourceId>

Returns all read dependencies as fetched from Self::fetch.

fn writes() -> Vec<ResourceId>

Returns all write dependencies as fetched from Self::fetch.