Trait Resource
pub trait Resource:
Send
+ Sync
+ 'static { }Expand description
A type that can be inserted into a [World] as a singleton.
You can access resource data in systems using the [Res] and [ResMut] system parameters
Only one resource of each type can be stored in a [World] at any given time.
§Examples
#[derive(Resource)]
struct MyResource { value: u32 }
world.insert_resource(MyResource { value: 42 });
fn read_resource_system(resource: Res<MyResource>) {
assert_eq!(resource.value, 42);
}
fn write_resource_system(mut resource: ResMut<MyResource>) {
assert_eq!(resource.value, 42);
resource.value = 0;
assert_eq!(resource.value, 0);
}§!Sync Resources
A !Sync type cannot implement Resource. However, it is possible to wrap a Send but not Sync
type in [SyncCell] or the currently unstable Exclusive to make it Sync. This forces only
having mutable access (&mut T only, never &T), but makes it safe to reference across multiple
threads.
This will fail to compile since RefCell is !Sync.
ⓘ
#[derive(Resource)]
struct NotSync {
counter: RefCell<usize>,
}This will compile since the RefCell is wrapped with SyncCell.
use bevy_utils::synccell::SyncCell;
#[derive(Resource)]
struct ActuallySync {
counter: SyncCell<RefCell<usize>>,
}