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https://github.com/bevyengine/bevy
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# Objective
When using `FromReflect`, fields can be optionally left out if they are
marked with `#[reflect(default)]`. This is very handy for working with
serialized data as giant structs only need to list a subset of defined
fields in order to be constructed.
<details>
<summary>Example</summary>
Take the following struct:
```rust
#[derive(Reflect, FromReflect)]
struct Foo {
#[reflect(default)]
a: usize,
#[reflect(default)]
b: usize,
#[reflect(default)]
c: usize,
#[reflect(default)]
d: usize,
}
```
Since all the fields are default-able, we can successfully call
`FromReflect` on deserialized data like:
```rust
(
"foo::Foo": (
// Only set `b` and default the rest
b: 123
)
)
```
</details>
Unfortunately, this does not work with fields in enum variants. Marking
a variant field as `#[reflect(default)]` does nothing when calling
`FromReflect`.
## Solution
Allow enum variant fields to define a default value using
`#[reflect(default)]`.
### `#[reflect(Default)]`
One thing that structs and tuple structs can do is use their `Default`
implementation when calling `FromReflect`. Adding `#[reflect(Default)]`
to the struct or tuple struct both registers `ReflectDefault` and alters
the `FromReflect` implementation to use `Default` to generate any
missing fields.
This works well enough for structs and tuple structs, but for enums it's
not as simple. Since the `Default` implementation for an enum only
covers a single variant, it's not as intuitive as to what the behavior
will be. And (imo) it feels weird that we would be able to specify
default values in this way for one variant but not the others.
Because of this, I chose to not implement that behavior here. However,
I'm open to adding it in if anyone feels otherwise.
---
## Changelog
- Allow enum variant fields to define a default value using
`#[reflect(default)]`
|
||
|---|---|---|
| .. | ||
| bevy_a11y | ||
| 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_gizmos | ||
| bevy_gltf | ||
| bevy_hierarchy | ||
| bevy_input | ||
| bevy_internal | ||
| bevy_log | ||
| bevy_macro_utils | ||
| bevy_macros_compile_fail_tests | ||
| 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 | ||