Struct specs::Read

pub struct Read<'a, T, F = DefaultProvider> where
    T: 'a,  { /* fields omitted */ }

Allows to fetch a resource in a system immutably.

If the resource isn't strictly required, you should use Option<Read<T>>.

Type parameters

• T: The type of the resource
• F: The setup handler (default: DefaultProvider)

Trait Implementations

impl<'a, T, F> SystemData<'a> for Read<'a, T, F> where
    F: SetupHandler<T>,
    T: Resource, 

fn setup(world: &mut World)

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

fn fetch(world: &'a World) -> Read<'a, T, F>

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.

impl<'a, T, F> From<Fetch<'a, T>> for Read<'a, T, F>

fn from(inner: Fetch<'a, T>) -> Read<'a, T, F>

Performs the conversion.

impl<'a, T, F> Deref for Read<'a, T, F> where
    T: Resource, 

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<'a, 'b, T> ParJoin for &'a Read<'b, T> where
    &'a T: ParJoin,
    T: Resource, 

fn par_join(self) -> JoinParIter<Self> where
    Self: Sized, 

Create a joined parallel iterator over the contents.

impl<'a, 'b, T> Join for &'a Read<'b, T> where
    &'a T: Join,
    T: Resource, 

type Type = <&'a T as Join>::Type

Type of joined components.

type Value = <&'a T as Join>::Value

Type of joined storages.

type Mask = <&'a T as Join>::Mask

Type of joined bit mask.

unsafe fn open(self) -> (Self::Mask, Self::Value)

Open this join by returning the mask and the storages.

unsafe fn get(v: &mut Self::Value, i: Index) -> Self::Type

Get a joined component value by a given index.

fn is_unconstrained() -> bool

If this Join typically returns all indices in the mask, then iterating over only it or combined with other joins that are also dangerous will cause the JoinIter/ParJoin to go through all indices which is usually not what is wanted and will kill performance.

Important traits for JoinIter<J>

impl<J: Join> Iterator for JoinIter<J> type Item = J::Type;

fn join(self) -> JoinIter<Self> where
    Self: Sized, 

Create a joined iterator over the contents.

fn maybe(self) -> MaybeJoin<Self> where
    Self: Sized, 

Returns a Join-able structure that yields all indices, returning None for all missing elements and Some(T) for found elements.