# Objective
Plugins are an incredible tool for encapsulating functionality. They are
low-key one of Bevy's best features. Combined with rust's module and
privacy system, it's a match made in heaven.
The one downside is that they can be a little too verbose to define. 90%
of all plugin definitions look something like this:
```rust
pub struct MyPlugin;
impl Plugin for MyPlugin {
fn build(&self, app: &mut App) {
app.init_resource::<CameraAssets>()
.add_event::<SetCamera>()
.add_systems(Update, (collect_set_camera_events, drive_camera).chain());
}
}
```
Every so often it gets a little spicier:
```rust
pub struct MyGenericPlugin<T>(PhantomData<T>);
impl<T> Default for MyGenericPlugin<T> {
fn default() -> Self { ... }
}
impl<T> Plugin for MyGenericPlugin<T> { ... }
```
This is an annoying amount of boilerplate. Ideally, plugins should be
focused and small in scope, which means any app is going to have a *lot*
of them. Writing a plugin should be as easy as possible, and the *only*
part of this process that carries any meaning is the body of `fn build`.
## Solution
Implement `Plugin` for functions that take `&mut App` as a parameter.
The two examples above now look like this:
```rust
pub fn my_plugin(app: &mut App) {
app.init_resource::<CameraAssets>()
.add_event::<SetCamera>()
.add_systems(Update, (collect_set_camera_events, drive_camera).chain());
}
pub fn my_generic_plugin<T>(app: &mut App) {
// No need for PhantomData, it just works.
}
```
Almost all plugins can be written this way, which I believe will make
bevy code much more attractive. Less boilerplate and less meaningless
indentation. More plugins with smaller scopes.
---
## Changelog
The `Plugin` trait is now implemented for all functions that take `&mut
App` as their only parameter. This is an abbreviated way of defining
plugins with less boilerplate than manually implementing the trait.
---------
Co-authored-by: Federico Rinaldi <gisquerin@gmail.com>
d66c868e6f
