mirror of
https://github.com/bevyengine/bevy
synced 2024-11-22 20:53:53 +00:00
992681b59b
*This PR description is an edited copy of #5007, written by @alice-i-cecile.* # Objective Follow-up to https://github.com/bevyengine/bevy/pull/2254. The `Resource` trait currently has a blanket implementation for all types that meet its bounds. While ergonomic, this results in several drawbacks: * it is possible to make confusing, silent mistakes such as inserting a function pointer (Foo) rather than a value (Foo::Bar) as a resource * it is challenging to discover if a type is intended to be used as a resource * we cannot later add customization options (see the [RFC](https://github.com/bevyengine/rfcs/blob/main/rfcs/27-derive-component.md) for the equivalent choice for Component). * dependencies can use the same Rust type as a resource in invisibly conflicting ways * raw Rust types used as resources cannot preserve privacy appropriately, as anyone able to access that type can read and write to internal values * we cannot capture a definitive list of possible resources to display to users in an editor ## Notes to reviewers * Review this commit-by-commit; there's effectively no back-tracking and there's a lot of churn in some of these commits. *ira: My commits are not as well organized :')* * I've relaxed the bound on Local to Send + Sync + 'static: I don't think these concerns apply there, so this can keep things simple. Storing e.g. a u32 in a Local is fine, because there's a variable name attached explaining what it does. * I think this is a bad place for the Resource trait to live, but I've left it in place to make reviewing easier. IMO that's best tackled with https://github.com/bevyengine/bevy/issues/4981. ## Changelog `Resource` is no longer automatically implemented for all matching types. Instead, use the new `#[derive(Resource)]` macro. ## Migration Guide Add `#[derive(Resource)]` to all types you are using as a resource. If you are using a third party type as a resource, wrap it in a tuple struct to bypass orphan rules. Consider deriving `Deref` and `DerefMut` to improve ergonomics. `ClearColor` no longer implements `Component`. Using `ClearColor` as a component in 0.8 did nothing. Use the `ClearColorConfig` in the `Camera3d` and `Camera2d` components instead. Co-authored-by: Alice <alice.i.cecile@gmail.com> Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> Co-authored-by: devil-ira <justthecooldude@gmail.com> Co-authored-by: Carter Anderson <mcanders1@gmail.com>
62 lines
2.1 KiB
Rust
62 lines
2.1 KiB
Rust
//! Allows reflection with trait objects.
|
|
|
|
use bevy::prelude::*;
|
|
|
|
fn main() {
|
|
App::new()
|
|
.add_plugins(DefaultPlugins)
|
|
.add_startup_system(setup)
|
|
.register_type::<MyType>()
|
|
.run();
|
|
}
|
|
|
|
#[derive(Reflect)]
|
|
#[reflect(DoThing)]
|
|
struct MyType {
|
|
value: String,
|
|
}
|
|
|
|
impl DoThing for MyType {
|
|
fn do_thing(&self) -> String {
|
|
format!("{} World!", self.value)
|
|
}
|
|
}
|
|
|
|
#[reflect_trait]
|
|
pub trait DoThing {
|
|
fn do_thing(&self) -> String;
|
|
}
|
|
|
|
fn setup(type_registry: Res<AppTypeRegistry>) {
|
|
// First, lets box our type as a Box<dyn Reflect>
|
|
let reflect_value: Box<dyn Reflect> = Box::new(MyType {
|
|
value: "Hello".to_string(),
|
|
});
|
|
|
|
// This means we no longer have direct access to MyType or its methods. We can only call Reflect
|
|
// methods on reflect_value. What if we want to call `do_thing` on our type? We could
|
|
// downcast using reflect_value.downcast_ref::<MyType>(), but what if we don't know the type
|
|
// at compile time?
|
|
|
|
// Normally in rust we would be out of luck at this point. Lets use our new reflection powers to
|
|
// do something cool!
|
|
let type_registry = type_registry.read();
|
|
|
|
// The #[reflect] attribute we put on our DoThing trait generated a new `ReflectDoThing` struct,
|
|
// which implements TypeData. This was added to MyType's TypeRegistration.
|
|
let reflect_do_thing = type_registry
|
|
.get_type_data::<ReflectDoThing>(reflect_value.type_id())
|
|
.unwrap();
|
|
|
|
// We can use this generated type to convert our `&dyn Reflect` reference to a `&dyn DoThing`
|
|
// reference
|
|
let my_trait: &dyn DoThing = reflect_do_thing.get(&*reflect_value).unwrap();
|
|
|
|
// Which means we can now call do_thing(). Magic!
|
|
info!("{}", my_trait.do_thing());
|
|
|
|
// This works because the #[reflect(MyTrait)] we put on MyType informed the Reflect derive to
|
|
// insert a new instance of ReflectDoThing into MyType's registration. The instance knows
|
|
// how to cast &dyn Reflect to &dyn MyType, because it knows that &dyn Reflect should first
|
|
// be downcasted to &MyType, which can then be safely casted to &dyn MyType
|
|
}
|