"with_children" does not support adding single component

[Raytwo]

Currently, the implementation requires that the component being spawned implemented DynamicBundle, so you can't do something like this:

fn setup(
    mut commands: Commands,
) {
    commands
        // Player
        .spawn(SpriteComponents {
            material: materials.add(Color::rgb(0.5, 0.0, 0.0).into()),
            translation: Translation(Vec3::new(window_desc.width as f32 / 2.0, 50.0, 0.0)),
            sprite: Sprite {
                size: Vec2::new(30.0, 30.0),
            },
            ..Default::default()
        })
        .with(Player::new())
        .with_children(|parent| {
            parent.spawn(BulletEmitter::new());
        });
}

Instead, you need to do it that way:

.with_children(|parent| {
            parent.spawn( (BulletEmitter::new(), ) );
        });
}

While this is a decent workaround, could it be possible to make it so you can use a regular Component too?

A friend suggested implementing the following, although I'm not knowledgeable about Rust enough to do so myself:
DynamicBundle for T: Component

Thanks!

[Ratysz]

This will run into duplicate implementation, partially because we don't have trait specialization (yet, potentially ever). T: Component bound means everything that can be a component - including all the tuples that DynamicBundle is implemented for elsewhere.

It can be circumvented with a "marker" generic parameter in DynamicBundle trait, but this could pollute all APIs that use DynamicBundle and potentially Bundle with that rather confusing parameter. I'm almost certain it won't come up in normal use of the public API, but it would show up in documentation.

[ryo33]

I thought about .with_child(BulletEmitter::new()), which wraps the current with_children, but it's too specific.

In that case, I prefer to;

• define BulletEmitterComponents.
• implement to_bundle(self) for BulletEmitter if it seems never used with other components.

[alice-i-cecile]

This should be solved with the new Commands API in 0.5. See #1703.

[alice-i-cecile]

Fixed in 0.5