Trait Combine

pub trait Combine<A: System, B: System> {
    type In: SystemInput;
    type Out;

    // Required method
    fn combine(
        input: <Self::In as SystemInput>::Inner<'_>,
        a: impl FnOnce(SystemIn<'_, A>) -> A::Out,
        b: impl FnOnce(SystemIn<'_, B>) -> B::Out,
    ) -> Self::Out;
}

Customizes the behavior of a CombinatorSystem.

Examples

use bevy_ecs::prelude::*;
use bevy_ecs::system::{CombinatorSystem, Combine};

// A system combinator that performs an exclusive-or (XOR)
// operation on the output of two systems.
pub type Xor<A, B> = CombinatorSystem<XorMarker, A, B>;

// This struct is used to customize the behavior of our combinator.
pub struct XorMarker;

impl<A, B> Combine<A, B> for XorMarker
where
    A: System<In = (), Out = bool>,
    B: System<In = (), Out = bool>,
{
    type In = ();
    type Out = bool;

    fn combine(
        _input: Self::In,
        a: impl FnOnce(A::In) -> A::Out,
        b: impl FnOnce(B::In) -> B::Out,
    ) -> Self::Out {
        a(()) ^ b(())
    }
}

app.add_systems(my_system.run_if(Xor::new(
    IntoSystem::into_system(resource_equals(A(1))),
    IntoSystem::into_system(resource_equals(B(1))),
    // The name of the combined system.
    std::borrow::Cow::Borrowed("a ^ b"),
)));

Required Associated Types

type In: SystemInput

The input type for a CombinatorSystem.

type Out

The output type for a CombinatorSystem.

Required Methods

fn combine( input: <Self::In as SystemInput>::Inner<'_>, a: impl FnOnce(SystemIn<'_, A>) -> A::Out, b: impl FnOnce(SystemIn<'_, B>) -> B::Out, ) -> Self::Out

When used in a CombinatorSystem, this function customizes how the two composite systems are invoked and their outputs are combined.

See the trait-level docs for Combine for an example implementation.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors