Add World::resource_scope_by_id

[Shatur]

What problem does this solve or what need does it fill?

I working on https://github.com/projectharmonia/bevy_replicon and we do a lot of type erasure internally for perfomance and a nice API.

Sometimes I need to access a resource mutably by ID and other resources just as reference. Since we don't have something like World::resource_scope_by_id, I do the inverse:

world.resource_scope(|world, registry: Mut<AppTypeRegistry>| {
    world.resource_scope(|world, entity_map: Mut<ServerEntityMap>| {
        world.resource_scope(|world, server_events: Mut<ServerEvents>| {
        });
    });
});

What solution would you like?

But it would be nicer to do it like this:

world.resource_scope_by_id(id, |world, resource| {
    let mut registry = world.resource::<AppTypeRegistry>();
    let mut entity_map = world.resource::<ServerEntityMap>();
    let mut server_events = world.resource::<ServerEvents>();
    // ...
});

[mnmaita]

Wondering if the World parameter in the closure should be non-mut for this requirement. And if so, would we still need to remove the Resource from the World like in resource_scope if we make World read-only?

[Shatur]

Wondering if the World parameter in the closure should be non-mut for this requirement.

I would keep it mutable for consistency with resource_scope. In this example I don't need it to be mutable, but there are some cases where it's needed.