# Objective
`AsBindGroup` can't be used as a trait object because of the constraint `Sized` and because of the associated function.
This is a problem for [`bevy_atmosphere`](https://github.com/JonahPlusPlus/bevy_atmosphere) because it needs to use a trait that depends on `AsBindGroup` as a trait object, for switching out different shaders at runtime. The current solution it employs is reimplementing the trait and derive macro into that trait, instead of constraining to `AsBindGroup`.
## Solution
Remove the `Sized` constraint from `AsBindGroup` and add the constraint `where Self: Sized` to the associated function `bind_group_layout`. Also change `PreparedBindGroup<T: AsBindGroup>` to `PreparedBindGroup<T>` and use it as `PreparedBindGroup<Self::Data>` instead of `PreparedBindGroup<Self>`.
This weakens the constraints, but increases the flexibility of `AsBindGroup`.
I'm not entirely sure why the `Sized` constraint was there, because it worked fine without it (maybe @cart wasn't aware of use cases for `AsBindGroup` as a trait object or this was just leftover from legacy code?).
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## Changelog
- `AsBindGroup` can be used as a trait object.
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