Data field should be optional

[EmiOnGit]

This is only my opinion so feel free to just close this issue :)

The problem

There are quite a lot of objects that don't need any input to be initialized because they are always initialized in the same way,
or only depend on a resource which would have to be fetched by the world in the spawn function anyway (I guess?).

I think a more idiomatic way would be to model it similar to how Query in bevy are modeled with the default value () if not given otherwise (for the filtering)

[janhohenheim]

You mean as in setting the data type to () by default and then requiring the signature of the spawn functions to be only fn spawn_stuffs(world: &mut World)?

[EmiOnGit]

Yes! As I prepared the example for issue #3 I thought it might have been nicer to not write ()

[janhohenheim]

Fixed by #5. Spawning functions are now just regular old Bevy systems with the user data being passed as an In, just like when you do piping.

New minimal example:

use bevy::prelude::*;
use spew::prelude::*;

#[derive(Debug, Eq, PartialEq)]
enum Object {
    Cube,
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugin(SpewPlugin::<Object>::default())
        .add_spawner((Object::Cube, spawn_cube))
        .add_system(spawn_something.on_startup())
        .run();
}

fn spawn_something(mut spawn_events: EventWriter<SpawnEvent<Object>>) {
    spawn_events.send(SpawnEvent::new(Object::Cube));
}

fn spawn_cube(mut commands: Commands) {
    info!("Spawning cube");
    commands.spawn(Name::new("Cube"));
}

New example with user data:

use bevy::prelude::*;
use spew::prelude::*;

#[derive(Debug, Eq, PartialEq)]
enum Object {
    Cube,
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugin(SpewPlugin::<Object, Transform>::default())
        .add_spawners(((Object::Cube, spawn_cube_with_transform),))
        .add_system(spawn_something_with_transform.on_startup())
        .run();
}

fn spawn_something_with_transform(mut spawn_events: EventWriter<SpawnEvent<Object, Transform>>) {
    spawn_events.send(SpawnEvent::with_data(
        Object::Cube,
        Transform::from_xyz(1.0, 2.0, 3.0),
    ));
}

fn spawn_cube_with_transform(In(transform): In<Transform>, mut commands: Commands) {
    info!("Spawning cube at {}", transform.translation);
    commands.spawn((Name::new("Cube"), transform));
}