Fixes #13466, implementing resource_scope_by_id

[Kugel-Blitz]

Objective

• Fixes Add World::resource_scope_by_id  #13466, implementing resource_scope_by_id

Testing

• Tested in the same way resource_scope was tested. Used the old precedent to test our new function by pulling the component id first and passing it in.

---

Showcase

Allows mutable retrieval of resources using component id in a way they are then inserted back into the world. Similar to resource_scope.

let mut world = World::default();

// Insert the resources into the world with initial values
world.insert_resource(MyResource { value: 42 });
world.insert_resource(MyOtherResource { value: 100 });

// Get the component ID for MyResource
let component_id = world
    .components()
    .get_resource_id(TypeId::of::<MyResource>())
    .expect("Failed to get component ID for MyResource");

println!("component_id of MyResource =  {}", component_id.index());

// Use resource_scope_by_id to modify MyResource safely
world.resource_scope_by_id(component_id, |world: &mut World, mut res: Mut<MyResource>| {
    println!("Resource before: {}", res.value);
    res.value += 10;  // Modify the res
    println!("Resource after modification: {}", res.value);

    // Now, let's access another resource inside the closure
    // Get the component ID for MyOtherResource
    let other_component_id = world
           .components()
           .get_resource_id(TypeId::of::<MyOtherResource>())
           .expect("Failed to get component ID for MyOtherResource");

    // Access MyOtherResource using resource_scope_by_id
    world.resource_scope_by_id(other_component_id, |_world: &mut World, mut other_res: Mut<MyResource>| {
        println!("Second Resource before: {}", other_res.value);
        other_res.value += 20;  // Modify the second resource
        println!("Second Resource after modification: {}", other_res.value);
    });
});

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[alice-i-cecile]

Suggested change

	/// /// # Example
	///
	/// # Example

Two points: you had an extra ///, and you were missing a newline before the heading. I suspect these are related!

[alice-i-cecile]

Suggested change

	/// struct B(u32);
	/// struct B(u32);
	///

[alice-i-cecile]

Suggested change

	/// #[derive(Resource)]
	///
	/// #[derive(Resource)]

[alice-i-cecile]

You should assert that you can't access A inside of this scope :)

[alice-i-cecile]

Suggested change

	/// See also [`try_resource_scope_by_id`](Self::try_resource_scope_by_id).
	/// See also [`try_resource_scope_by_id`](Self::try_resource_scope_by_id) for a non-panicking variant.

[alice-i-cecile]

These docs would benefit from a # Panics section :)

[alice-i-cecile]

In general, we're trying to move away from implicit panics, and towards explicit error handling. I think that we should collapse this down into one method, which returns an Option here. That added safety + hassle + lower API surface is appropriate for a niche tool like this.

[notmd]

The callback should accept MutUntyped instead. If you already know the concrete type why would you still use dynamic API?

[mhsalem36]

Hi @notmd, if we use MutUntyped. How could we read the ptr's value?
let mut value = unsafe { ptr.read::<R>() };

[notmd]

Hi sorry I totally forgot this. MutUntyped can construct directly with PtrMut, you don't need to read to concrete type. See https://dev-docs.bevyengine.org/bevy/ecs/change_detection/struct.MutUntyped.html