mirror of
https://github.com/bevyengine/bevy
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101 lines
3.8 KiB
Rust
101 lines
3.8 KiB
Rust
//! Illustrates how "reflection" works in Bevy.
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//!
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//! Reflection provides a way to dynamically interact with Rust types, such as accessing fields
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//! by their string name. Reflection is a core part of Bevy and enables a number of interesting
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//! features (like scenes).
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use bevy::{
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prelude::*,
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reflect::{
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serde::{ReflectSerializer, UntypedReflectDeserializer},
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DynamicStruct,
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},
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};
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use serde::de::DeserializeSeed;
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.register_type::<Foo>()
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.register_type::<Bar>()
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.add_systems(Startup, setup)
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.run();
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}
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/// Deriving `Reflect` implements the relevant reflection traits. In this case, it implements the
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/// `Reflect` trait and the `Struct` trait `derive(Reflect)` assumes that all fields also implement
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/// Reflect.
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#[derive(Reflect)]
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pub struct Foo {
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a: usize,
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nested: Bar,
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#[reflect(ignore)]
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_ignored: NonReflectedValue,
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}
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/// This `Bar` type is used in the `nested` field on the `Test` type. We must derive `Reflect` here
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/// too (or ignore it)
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#[derive(Reflect)]
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pub struct Bar {
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b: usize,
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}
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pub struct NonReflectedValue {
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_a: usize,
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}
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fn setup(type_registry: Res<AppTypeRegistry>) {
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let mut value = Foo {
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a: 1,
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_ignored: NonReflectedValue { _a: 10 },
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nested: Bar { b: 8 },
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};
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// You can set field values like this. The type must match exactly or this will fail.
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*value.get_field_mut("a").unwrap() = 2usize;
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assert_eq!(value.a, 2);
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assert_eq!(*value.get_field::<usize>("a").unwrap(), 2);
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// You can also get the &dyn Reflect value of a field like this
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let field = value.field("a").unwrap();
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// you can downcast Reflect values like this:
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assert_eq!(*field.downcast_ref::<usize>().unwrap(), 2);
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// DynamicStruct also implements the `Struct` and `Reflect` traits.
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let mut patch = DynamicStruct::default();
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patch.insert("a", 4usize);
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// You can "apply" Reflect implementations on top of other Reflect implementations.
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// This will only set fields with the same name, and it will fail if the types don't match.
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// You can use this to "patch" your types with new values.
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value.apply(&patch);
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assert_eq!(value.a, 4);
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let type_registry = type_registry.read();
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// By default, all derived `Reflect` types can be Serialized using serde. No need to derive
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// Serialize!
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let serializer = ReflectSerializer::new(&value, &type_registry);
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let ron_string =
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ron::ser::to_string_pretty(&serializer, ron::ser::PrettyConfig::default()).unwrap();
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info!("{}\n", ron_string);
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// Dynamic properties can be deserialized
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let reflect_deserializer = UntypedReflectDeserializer::new(&type_registry);
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let mut deserializer = ron::de::Deserializer::from_str(&ron_string).unwrap();
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let reflect_value = reflect_deserializer.deserialize(&mut deserializer).unwrap();
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// Deserializing returns a Box<dyn Reflect> value. Generally, deserializing a value will return
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// the "dynamic" variant of a type. For example, deserializing a struct will return the
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// DynamicStruct type. "Value types" will be deserialized as themselves.
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let _deserialized_struct = reflect_value.downcast_ref::<DynamicStruct>();
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// Reflect has its own `partial_eq` implementation, named `reflect_partial_eq`. This behaves
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// like normal `partial_eq`, but it treats "dynamic" and "non-dynamic" types the same. The
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// `Foo` struct and deserialized `DynamicStruct` are considered equal for this reason:
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assert!(reflect_value.reflect_partial_eq(&value).unwrap());
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// By "patching" `Foo` with the deserialized DynamicStruct, we can "Deserialize" Foo.
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// This means we can serialize and deserialize with a single `Reflect` derive!
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value.apply(&*reflect_value);
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}
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