Objective

^ enable this

Concretely, I need to

list all handle ids for an asset type
fetch the asset as dyn Reflect, given a HandleUntyped
when encountering a Handle<T>, find out what asset type that handle refers to (T's type id) and turn the handle into a HandleUntyped

Solution

add ReflectAsset type containing function pointers for working with assets

pub struct ReflectAsset {
    type_uuid: Uuid,
    assets_resource_type_id: TypeId, // TypeId of the `Assets<T>` resource

    get: fn(&World, HandleUntyped) -> Option<&dyn Reflect>,
    get_mut: fn(&mut World, HandleUntyped) -> Option<&mut dyn Reflect>,
    get_unchecked_mut: unsafe fn(&World, HandleUntyped) -> Option<&mut dyn Reflect>,
    add: fn(&mut World, &dyn Reflect) -> HandleUntyped,
    set: fn(&mut World, HandleUntyped, &dyn Reflect) -> HandleUntyped,
    len: fn(&World) -> usize,
    ids: for<'w> fn(&'w World) -> Box<dyn Iterator<Item = HandleId> + 'w>,
    remove: fn(&mut World, HandleUntyped) -> Option<Box<dyn Reflect>>,
}

add ReflectHandle type relating the handle back to the asset type and providing a way to create a HandleUntyped

pub struct ReflectHandle {
    type_uuid: Uuid,
    asset_type_id: TypeId,
    downcast_handle_untyped: fn(&dyn Any) -> Option<HandleUntyped>,
}

add the corresponding FromType impls
add a function app.register_asset_reflect which is supposed to be called after .add_asset and registers ReflectAsset and ReflectHandle in the type registry

Changelog

add ReflectAsset and ReflectHandle types, which allow code to use reflection to manipulate arbitrary assets without knowing their types at compile time

Sep 09 '22 12:09 jakobhellermann

I'm in favor of this! Just some small comments around ergonomics and docs.

Sep 09 '22 13:09 alice-i-cecile

One question I just thought of is if we want to represent owned values in these kinds of APIs as &Reflect with the expectation that we will just call FromReflect on it, or as Box<dyn Reflect> which we assume to be containing exactly the wanted type. If the later, we probably need ReflectFromReflect for people who want to use FromReflect dynamically (part of https://github.com/bevyengine/bevy/pull/6056).

Oct 06 '22 20:10 jakobhellermann

Big :+1: to this! This is exactly what I was needing for asset management in scripts.

Oct 06 '22 21:10 zicklag

One question I just thought of is if we want to represent owned values in these kinds of APIs as &Reflect with the expectation that we will just call FromReflect on it, or as Box<dyn Reflect> which we assume to be containing exactly the wanted type.

My instinct is that I should have a Box<dyn Reflect> for owned values, and ReflectFromReflect was another thing I ran into the need for earlier.

To work around not having ReflectFromReflect I ended up trying to combine ReflectDefault to create the value and Reflect.apply() to patch the value.

Oct 06 '22 21:10 zicklag

@jakobhellermann I think this PR needs to be rebased

Oct 25 '22 20:10 MrGVSV

bors r+

Oct 28 '22 20:10 cart

Pull request successfully merged into main.

Build succeeded:

Oct 28 '22 21:10 bors[bot]

add `ReflectAsset` and `ReflectHandle`

Objective

Solution

Changelog