Cast query of mutable components to query of immutable

[michalmoc]

Because of Rust borrow checker I'm usually forced to pass around entities and queries. But there seems to be a problem when I've got a mutable query but it suffices to have immutable one, like

fn some_function(entities: &Vec<Entity>, query: &Query<&SomeComponent>){...}

fn some_system(some_entities: Res<Vec<Entity>>, query: Query<&mut SomeComponent>)
{
    for mut c in query.iter_mut() {...};

    some_function(some_entities, query);
}

As far as I can see there is no way to cast the query although it seems reasonable to do so. I believe there should exist some implementation of AsRef trait or perhaps some new trait like CanQuery<ComponentType>.

[alice-i-cecile]

I agree here. I'd really like to see a unified API for casting mutable ECS data into its immutable form, in order to resolve this sort of challenge. You see this with e.g. ResMut and NonSendMut as well.