impl EntityCommand for Arc<dyn Fn(EntityWorldMut) ...>

[Person-93]

Objective

A Box<dyn Fn(EntityWorldMut) -> Out + Send + 'static> can already be used as an EntityCommand, but an Arc can't.

Solution

Add an implementation for Arc.

Testing

None

[alice-i-cecile]

Can you say a bit more about why you wanted this? Presumably a heavy or not thread-safe command?

[ItsDoot]

LGTM, although I would make the following addition to relax its bounds a bit.

Also interested to here your motivation!

[Person-93]

I want to have something like this.

#[derive(Resource)]
struct DynamicEntityCommands(Vec<Arc<dyn Fn(EntityWorldMut) -> Result + Send + Sync + 'static>>);

[chescock]

A Box<dyn Fn(EntityWorldMut) -> Out + Send + 'static> can already be used as an EntityCommand, but an Arc can't.

Note that another option is to convert the Arc<dyn Fn...> to an EntityCommand by wrapping it in a closure, like move |e: EntityWorldMut| arc(e).

---

I want to have something like this.

#[derive(Resource)]
struct DynamicEntityCommands(Vec<Arc<dyn Fn(EntityWorldMut) -> Result + Send + Sync + 'static>>);

I'm not sure whether this will actually be helpful for your use case, but if your commands are cheap to clone and you want to do some premature optimization, then another option is to wrap queue() in an Fn(EntityCommands) before erasing the type. That avoids the atomic operations for Arc::clone and can avoid memory allocation for ZST commands.

#[derive(Resource)]
struct DynamicEntityCommands(Vec<Box<dyn Fn(EntityCommands) + Send + Sync + 'static>>);

impl DynamicEntityCommands {
    fn queue(&mut self, c: impl EntityCommand + Clone + Sync) {
        self.0.push(Box::new(move |mut entity_commands| {
            entity_commands.queue(c.clone());
        }));
    }

    fn apply(&self, mut entity_commands: EntityCommands) {
        for f in &self.0 {
            f(entity_commands.reborrow());
        }
    }
}