# Objective
Fix#9747
## Solution
Linkers don't like what we're doing with CowArc (I'm guessing it has
something to do with `?Sized`). Weirdly the `Reflect` derive on
`AssetPath` doesn't fail, despite `CowArc` not implementing `Reflect`.
To resolve this, we manually implement "reflect value" for
`AssetPath<'static>`. It sadly cannot use `impl_reflect_value` because
that macro doesn't support static lifetimes.
---------
Co-authored-by: Martin Dickopp <martin@zero-based.org>
# Objective
The `AssetServer` and `AssetProcessor` do a lot of `AssetPath` cloning
(across many threads). To store the path on the handle, to store paths
in dependency lists, to pass an owned path to the offloaded thread, to
pass a path to the LoadContext, etc , etc. Cloning multiple string
allocations multiple times like this will add up. It is worth optimizing
this.
Referenced in #9714
## Solution
Added a new `CowArc<T>` type to `bevy_util`, which behaves a lot like
`Cow<T>`, but the Owned variant is an `Arc<T>`. Use this in place of
`Cow<str>` and `Cow<Path>` on `AssetPath`.
---
## Changelog
- `AssetPath` now internally uses `CowArc`, making clone operations much
cheaper
- `AssetPath` now serializes as `AssetPath("some_path.extension#Label")`
instead of as `AssetPath { path: "some_path.extension", label:
Some("Label) }`
## Migration Guide
```rust
// Old
AssetPath::new("logo.png", None);
// New
AssetPath::new("logo.png");
// Old
AssetPath::new("scene.gltf", Some("Mesh0");
// New
AssetPath::new("scene.gltf").with_label("Mesh0");
```
`AssetPath` now serializes as `AssetPath("some_path.extension#Label")`
instead of as `AssetPath { path: "some_path.extension", label:
Some("Label) }`
---------
Co-authored-by: Pascal Hertleif <killercup@gmail.com>
