Bevy Mutually Exclusive Components

Mutually exclusive groups of components for bevy.

Usage

There is no plugin, just bring the RegisterMutuallyExclusiveComponent trait into scope:

use bevy_mutually_exclusive_components::prelude::*;

Components in a group (defined by a u32) are mutually exclusive – if you set up a group with components A, B, and C, then insert A into an entity, then insert B, A will be removed.

#[derive(Component)]
struct A;
#[derive(Component)]
struct B;
#[derive(Component)]
struct C;

// ...

// Make components A,B,C mutually exclusive
const MY_GROUP: u32 = 1;
app.register_mutually_exclusive_component::<MY_GROUP, A>();
app.register_mutually_exclusive_component::<MY_GROUP, B>();
app.register_mutually_exclusive_component::<MY_GROUP, C>();

// Make components X,Y mutually exclusive
const MY_OTHER_GROUP: u32 = 2;
app.register_mutually_exclusive_component::<MY_OTHER_GROUP, X>();
app.register_mutually_exclusive_component::<MY_OTHER_GROUP, Y>();

How it works

A component hook is created for each component you register. It stores the ComponentId of itself in a private LastMutuallyExclusiveId component on insertion.

Before doing so, it checks if there is already a value in the LastMutuallyExclusiveId component, and if so, removes the component with that ComponentId.

See the test at the bottom of lib.rs for an example.

The LastMutuallyExclusiveId component takes a const generic u32, which is how groups are identified.

Caution

Components can only have one hook, so it'll panic if you try to add a component to multiple groups.

It will also panic if a component already has a hook for another reason.

License

Same as bevy