bevy/crates/bevy_reflect
dependabot[bot] a6ec32aca4
Update erased-serde requirement from 0.3 to 0.4 (#11599)
Updates the requirements on
[erased-serde](https://github.com/dtolnay/erased-serde) to permit the
latest version.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/dtolnay/erased-serde/releases">erased-serde's
releases</a>.</em></p>
<blockquote>
<h2>0.4.2</h2>
<ul>
<li>Update proc-macro2 to fix caching issue when using a rustc-wrapper
such as sccache</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="8f555a2db2"><code>8f555a2</code></a>
Release 0.4.2</li>
<li><a
href="450a9108fc"><code>450a910</code></a>
Pull in proc-macro2 sccache fix</li>
<li><a
href="4726cdb49d"><code>4726cdb</code></a>
Release 0.4.1</li>
<li><a
href="4e04e70902"><code>4e04e70</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/erased-serde/issues/101">#101</a>
from dtolnay/sererror</li>
<li><a
href="c670c72da5"><code>c670c72</code></a>
Preserve error message of errors originated from Serialize impl</li>
<li><a
href="6893670cca"><code>6893670</code></a>
Ignore box_collection clippy lint</li>
<li><a
href="7ddf6aadd8"><code>7ddf6aa</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/erased-serde/issues/100">#100</a>
from KodrAus/fix/failing-serialize-impl</li>
<li><a
href="8227d20573"><code>8227d20</code></a>
handle the case where a Serialize fails without calling the
Serializer</li>
<li><a
href="160c15393e"><code>160c153</code></a>
Release 0.4.0</li>
<li><a
href="2e48977019"><code>2e48977</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/erased-serde/issues/99">#99</a>
from dtolnay/bench</li>
<li>Additional commits viewable in <a
href="https://github.com/dtolnay/erased-serde/compare/0.3.0...0.4.2">compare
view</a></li>
</ul>
</details>
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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
2024-01-29 19:03:55 +00:00
..
bevy_reflect_derive bevy_reflect: Split #[reflect(where)] (#11597) 2024-01-29 17:54:17 +00:00
examples fix nightly clippy warnings (#6395) 2022-10-28 21:03:01 +00:00
src bevy_reflect: Split #[reflect(where)] (#11597) 2024-01-29 17:54:17 +00:00
Cargo.toml Update erased-serde requirement from 0.3 to 0.4 (#11599) 2024-01-29 19:03:55 +00:00
README.md add and fix shields in Readmes (#9993) 2023-10-15 00:52:31 +00:00

Bevy Reflect

License Crates.io Downloads Docs Discord

This crate enables you to dynamically interact with Rust types:

  • Derive the Reflect traits
  • Interact with fields using their names (for named structs) or indices (for tuple structs)
  • "Patch" your types with new values
  • Look up nested fields using "path strings"
  • Iterate over struct fields
  • Automatically serialize and deserialize via Serde (without explicit serde impls)
  • Trait "reflection"

Features

Derive the Reflect traits

// this will automatically implement the Reflect trait and the Struct trait (because the type is a struct)
#[derive(Reflect)]
struct Foo {
    a: u32,
    b: Bar,
    c: Vec<i32>,
    d: Vec<Baz>,
}

// this will automatically implement the Reflect trait and the TupleStruct trait (because the type is a tuple struct)
#[derive(Reflect)]
struct Bar(String);

#[derive(Reflect)]
struct Baz {
    value: f32,
}

// We will use this value to illustrate `bevy_reflect` features
let mut foo = Foo {
    a: 1,
    b: Bar("hello".to_string()),
    c: vec![1, 2],
    d: vec![Baz { value: 3.14 }],
};

Interact with fields using their names

assert_eq!(*foo.get_field::<u32>("a").unwrap(), 1);

*foo.get_field_mut::<u32>("a").unwrap() = 2;

assert_eq!(foo.a, 2);

"Patch" your types with new values

let mut dynamic_struct = DynamicStruct::default();
dynamic_struct.insert("a", 42u32);
dynamic_struct.insert("c", vec![3, 4, 5]);

foo.apply(&dynamic_struct);

assert_eq!(foo.a, 42);
assert_eq!(foo.c, vec![3, 4, 5]);

Look up nested fields using "path strings"

let value = *foo.get_path::<f32>("d[0].value").unwrap();
assert_eq!(value, 3.14);

Iterate over struct fields

for (i, value: &Reflect) in foo.iter_fields().enumerate() {
    let field_name = foo.name_at(i).unwrap();
    if let Some(value) = value.downcast_ref::<u32>() {
        println!("{} is a u32 with the value: {}", field_name, *value);
    }
}

Automatically serialize and deserialize via Serde (without explicit serde impls)

let mut registry = TypeRegistry::default();
registry.register::<u32>();
registry.register::<i32>();
registry.register::<f32>();
registry.register::<String>();
registry.register::<Bar>();
registry.register::<Baz>();

let serializer = ReflectSerializer::new(&foo, &registry);
let serialized = ron::ser::to_string_pretty(&serializer, ron::ser::PrettyConfig::default()).unwrap();

let mut deserializer = ron::de::Deserializer::from_str(&serialized).unwrap();
let reflect_deserializer = ReflectDeserializer::new(&registry);
let value = reflect_deserializer.deserialize(&mut deserializer).unwrap();
let dynamic_struct = value.take::<DynamicStruct>().unwrap();

assert!(foo.reflect_partial_eq(&dynamic_struct).unwrap());

Trait "reflection"

Call a trait on a given &dyn Reflect reference without knowing the underlying type!

#[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;
}

// 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 mut type_registry = TypeRegistry::default();
type_registry.register::<MyType>();

// 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!
println!("{}", 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 DoThing, because it
// knows that &dyn Reflect should first be downcasted to &MyType, which can then be safely casted to &dyn DoThing

Why make this?

The whole point of Rust is static safety! Why build something that makes it easy to throw it all away?

  • Some problems are inherently dynamic (scripting, some types of serialization / deserialization)
  • Sometimes the dynamic way is easier
  • Sometimes the dynamic way puts less burden on your users to derive a bunch of traits (this was a big motivator for the Bevy project)