Struct bevy::ecs::system::StaticSystemParam

pub struct StaticSystemParam<'w, 's, P>(_)
where
    P: SystemParam;

A helper for using system parameters in generic contexts

This type is a SystemParam adapter which always has Self::Fetch::Item == Self (ignoring lifetimes for brevity), no matter the argument SystemParam (P) (other than that P must be 'static)

This makes it useful for having arbitrary SystemParam type arguments to function systems, or for generic types using the SystemParam derive:

use bevy_ecs::system::{SystemParam, StaticSystemParam};
#[derive(SystemParam)]
struct GenericParam<'w,'s, T: SystemParam + 'static> {
    field: StaticSystemParam<'w, 's, T>,
}
fn do_thing_generically<T: SystemParam + 'static>(t: StaticSystemParam<T>) {}

fn check_always_is_system<T: SystemParam + 'static>(){
    bevy_ecs::system::assert_is_system(do_thing_generically::<T>);
}

Note that in a real case you’d generally want additional bounds on P, for your use of the parameter to have a reason to be generic.

For example, using this would allow a type to be generic over whether a resource is accessed mutably or not, with impls being bounded on P: Deref<Target=MyType>, and P: DerefMut<Target=MyType> depending on whether the method requires mutable access or not.

The method which doesn’t use this type will not compile:

fn do_thing_generically<T: SystemParam + 'static>(t: T) {}

#[derive(SystemParam)]
struct GenericParam<'w,'s, T: SystemParam> {
    field: T,
    #[system_param(ignore)]
    // Use the lifetimes, as the `SystemParam` derive requires them
    phantom: core::marker::PhantomData<&'w &'s ()>
}

Implementations

impl<'w, 's, P> StaticSystemParam<'w, 's, P>where
    P: SystemParam,

pub fn into_inner(
    self
) -> <<P as SystemParam>::Fetch as SystemParamFetch<'w, 's>>::Item

Get the value of the parameter

Trait Implementations

impl<'w, 's, P> Deref for StaticSystemParam<'w, 's, P>where
    P: SystemParam,

type Target = <<P as SystemParam>::Fetch as SystemParamFetch<'w, 's>>::Item

The resulting type after dereferencing.

fn deref(&self) -> &<StaticSystemParam<'w, 's, P> as Deref>::Target

Dereferences the value.

impl<'w, 's, P> DerefMut for StaticSystemParam<'w, 's, P>where
    P: SystemParam,

fn deref_mut(&mut self) -> &mut <StaticSystemParam<'w, 's, P> as Deref>::Target

Mutably dereferences the value.

impl<'world, 'state, P> SystemParam for StaticSystemParam<'world, 'state, P>where
    P: 'static + SystemParam,

type Fetch = StaticSystemParamState<<P as SystemParam>::Fetch, P>