impl SceneList for Vec<Box<dyn SceneList>>

[chronicl]

Objective

I couldn't figure out a way to spawn a variable amount of SceneLists as Children.

This came up when trying to make a variable row grid layout, each row being a SceneList because it has columns that need to be inserted directly into the grid Node:

let rows: Vec<Box<dyn SceneList>> = ...;
bsn! {
    Node { display: Display::Grid }
    // This doesn't work
    Children [ { rows } ]
}

Solution

impl SceneList for Vec<Box<dyn SceneList>> { ... }

This can be implemented in user land by creating a wrapper type for Vec<Box<dyn SceneList>>, so I don't feel strongly about actually merging this PR.

Testing

None so far.

[chronicl]

Actually, a better solution that can avoid Boxing if the SceneList types are homogenous is to create a

#[derive(Deref, DerefMut)]
struct VecSceneList<S>(pub Vec<S>);

impl<S: SceneList> SceneList for VecSceneList<S> { ... }

// Convenience method for when the `SceneList` types aren't homogenous (and thus Box is required)
impl VecSceneList<Box<dyn SceneList>> {
    fn push_box(&mut self, scene_list: impl SceneList) { self.push(Box::new(scene_list) }
}

but this can be implemented in user land. I'm not sure if bevy wants to provide these kind of helper types?

[villejuutila]

It should be possible to pass Vec<impl Scene> for Children already.

[chronicl]

It should be possible to pass Vec<impl Scene> for Children already.

I need Vec<impl SceneList> to implement SceneList (not Vec<impl Scene>), which is trivial to implement, however

// We already have
impl<S: Scene> SceneList for Vec<S>
// so we can't also have
impl<S: SceneList> SceneList for Vec<S>
// because there could be types that are S: Scene + SceneList and rust doesn't have specialization