seldom_fn_plugin

seldom_fn_plugin allows using Rust functions in place of Bevy plugins without sacrificing the builder pattern. This improves the ergonomics of plugin-heavy apps and makes it possible to avoid certain .clone()s while maintaining modularity.

I would advise against replacing Bevy plugins with fn_plugins in a public API. It is better to keep consistent with the rest of the Bevy ecosystem in this case. However, you may expose both and just have the Bevy plugin add the fn_plugin.

The code for this crate is only 10 lines, excluding docs and whitespace, so you can avoid adding a dependency by just copying the code into your project. I decided to publish it despite its length for a few reasons. First, I want to see people use this pattern. Second, I work on many Bevy projects, and would like to reduce the duplication of this code. Finally, I intend to publish more crates, so it doesn't hurt to get familiar with the process.

Usage

# Replace * with your desired version

[dependencies]
seldom_fn_plugin = "*"

See the examples below for example usage.

Compatibility

Examples

Here is an example usage:

use bevy::prelude::*;
use seldom_fn_plugin::FnPluginExt;

fn say_hi() {
    println!("hi");
}

fn my_plugin(app: &mut App) {
    app.add_system(say_hi);
}

fn main() {
    App::new().fn_plugin(my_plugin).run();
}

Here are some examples from a game and some other crates I'm developing:

Before:

pub struct ControlsPlugin;

impl Plugin for ControlsPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<Controls>();
    }
}

After:

pub fn controls_plugin(app: &mut App) {
    app.init_resource::<Controls>();
}

Before:

pub(crate) struct AssetPlugin;

impl Plugin for AssetPlugin {
    fn build(&self, app: &mut App) {
        app.add_plugin(PxAssetPlugin::<PxSpriteData>::default())
            .add_plugin(PxAssetPlugin::<PxTilesetData>::default())
            .add_plugin(PxAssetPlugin::<PxTypefaceData>::default())
            .add_plugin(PxAssetPlugin::<PxFilterData>::default());
    }
}

struct PxAssetPlugin<D: PxAssetData>(PhantomData<D>);

impl<D: PxAssetData> Plugin for PxAssetPlugin<D> {
    fn build(&self, app: &mut App) {
        app.add_asset::<PxAsset<D>>()
            .init_resource::<LoadingAssets<D>>()
            .add_system(D::load.in_set(PxSet::LoadAssets));
    }
}

impl<D: PxAssetData> Default for PxAssetPlugin<D> {
    fn default() -> Self {
        Self(default())
    }
}

After (avoids an annoying PhantomData):

pub(crate) fn asset_plugin(app: &mut App) {
    app.fn_plugin(px_asset_plugin::<PxSpriteData>)
        .fn_plugin(px_asset_plugin::<PxTilesetData>)
        .fn_plugin(px_asset_plugin::<PxTypefaceData>)
        .fn_plugin(px_asset_plugin::<PxFilterData>);
}

fn px_asset_plugin<D: PxAssetData>(app: &mut App) {
    app.add_asset::<PxAsset<D>>()
        .init_resource::<LoadingAssets<D>>()
        .add_system(D::load.in_set(PxSet::LoadAssets));
}

Before:

pub(crate) struct CollisionPlugin<G: PxCollisionGroup> {
    listeners: HashMap<G, HashSet<G>>,
    resolvers: HashMap<G, HashSet<G>>,
}

impl<G: PxCollisionGroup> Plugin for CollisionPlugin<G> {
    fn build(&self, app: &mut App) {
        app.add_event::<PxCollision>().add_system(detect_collisions(
            self.listeners.clone(),
            self.resolvers.clone(),
        ));
    }
}

impl<G: PxCollisionGroup> CollisionPlugin<G> {
    pub(crate) fn new(
        listeners: HashMap<G, HashSet<G>>,
        resolvers: HashMap<G, HashSet<G>>,
    ) -> Self {
        Self {
            listeners,
            resolvers,
        }
    }
}

After (avoids a couple .clone()s):

pub(crate) fn collision_plugin<G: PxCollisionGroup>(
    listeners: HashMap<G, HashSet<G>>,
    resolvers: HashMap<G, HashSet<G>>,
) -> impl FnOnce(&mut App) {
    |app| {
        app.add_event::<PxCollision>()
            .add_system(detect_collisions(listeners, resolvers));
    }
}

License

seldom_fn_plugin is dual-licensed under MIT and Apache 2.0 at your option.