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https://github.com/bevyengine/bevy
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cbb4c26cad
# Objective
I recently had an issue, where I have a struct:
```
struct Property {
inner: T
}
```
that I use as a wrapper for internal purposes.
I don't want to update my struct definition to
```
struct Property<T: Reflect>{
inner: T
}
```
because I still want to be able to build `Property<T>` for types `T` that are not `Reflect`. (and also because I don't want to update my whole code base with `<T: Reflect>` bounds)
I still wanted to have reflection on it (for `bevy_inspector_egui`), but adding `derive(Reflect)` fails with the error:
`T cannot be sent between threads safely. T needs to implement Sync.`
I believe that `bevy_reflect` should adopt the model of other derives in the case of generics, which is to add the `Reflect` implementation only if the generics also implement `Reflect`. (That is the behaviour of other macros such as `derive(Clone)` or `derive(Debug)`.
It's also the current behavior of `derive(FromReflect)`.
Basically doing something like:
```
impl<T> Reflect for Foo<T>
where T: Reflect
```
## Solution
- I updated the derive macros for `Structs` and `TupleStructs` to add extra `where` bounds.
- Every type that is reflected will need a `T: Reflect` bound
- Ignored types will need a `T: 'static + Send + Sync` bound. Here's the reason. For cases like this:
```
#[derive(Reflect)]
struct Foo<T, U>{
a: T
#[reflect(ignore)]
b: U
}
```
I had to add the bound `'static + Send + Sync` to ignored generics like `U`.
The reason is that we want `Foo<T, U>` to be `Reflect: 'static + Send + Sync`, so `Foo<T, U>` must be able to implement those auto-traits. `Foo<T, U>` will only implement those auto-traits if every generic type implements them, including ignored types.
This means that the previously compile-fail case now compiles:
```
#[derive(Reflect)]
struct Foo<'a> {
#[reflect(ignore)]
value: &'a str,
}
```
But `Foo<'a>` will only be useable in the cases where `'a: 'static` and panic if we don't have `'a: 'static`, which is what we want (nice bonus from this PR ;) )
---
## Changelog
> This section is optional. If this was a trivial fix, or has no externally-visible impact, you can delete this section.
### Added
Possibility to add `derive(Reflect)` to structs and enums that contain generic types, like so:
```
#[derive(Reflect)]
struct Foo<T>{
a: T
}
```
Reflection will only be available if the generic type T also implements `Reflect`.
(previously, this would just return a compiler error)
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| .. | ||
| bevy_animation | ||
| bevy_app | ||
| bevy_asset | ||
| bevy_audio | ||
| bevy_core | ||
| bevy_core_pipeline | ||
| bevy_derive | ||
| bevy_diagnostic | ||
| bevy_dylib | ||
| bevy_dynamic_plugin | ||
| bevy_ecs | ||
| bevy_ecs_compile_fail_tests | ||
| bevy_encase_derive | ||
| bevy_gilrs | ||
| bevy_gltf | ||
| bevy_hierarchy | ||
| bevy_input | ||
| bevy_internal | ||
| bevy_log | ||
| bevy_macro_utils | ||
| bevy_math | ||
| bevy_mikktspace | ||
| bevy_pbr | ||
| bevy_ptr | ||
| bevy_reflect | ||
| bevy_reflect_compile_fail_tests | ||
| bevy_render | ||
| bevy_scene | ||
| bevy_sprite | ||
| bevy_tasks | ||
| bevy_text | ||
| bevy_time | ||
| bevy_transform | ||
| bevy_ui | ||
| bevy_utils | ||
| bevy_window | ||
| bevy_winit | ||