1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126
use crate::{FromType, Reflect};
/// A trait that enables types to be dynamically constructed from reflected data.
///
/// It's recommended to use the [derive macro] rather than manually implementing this trait.
///
/// `FromReflect` allows dynamic proxy types, like [`DynamicStruct`], to be used to generate
/// their concrete counterparts.
/// It can also be used to partially or fully clone a type (depending on whether it has
/// ignored fields or not).
///
/// In some cases, this trait may even be required.
/// Deriving [`Reflect`] on an enum requires all its fields to implement `FromReflect`.
/// Additionally, some complex types like `Vec<T>` require that their element types
/// implement this trait.
/// The reason for such requirements is that some operations require new data to be constructed,
/// such as swapping to a new variant or pushing data to a homogeneous list.
///
/// See the [crate-level documentation] to see how this trait can be used.
///
/// [derive macro]: bevy_reflect_derive::FromReflect
/// [`DynamicStruct`]: crate::DynamicStruct
/// [crate-level documentation]: crate
#[diagnostic::on_unimplemented(
message = "`{Self}` can not be created through reflection",
note = "consider annotating `{Self}` with `#[derive(FromReflect)]`"
)]
pub trait FromReflect: Reflect + Sized {
/// Constructs a concrete instance of `Self` from a reflected value.
fn from_reflect(reflect: &dyn Reflect) -> Option<Self>;
/// Attempts to downcast the given value to `Self` using,
/// constructing the value using [`from_reflect`] if that fails.
///
/// This method is more efficient than using [`from_reflect`] for cases where
/// the given value is likely a boxed instance of `Self` (i.e. `Box<Self>`)
/// rather than a boxed dynamic type (e.g. [`DynamicStruct`], [`DynamicList`], etc.).
///
/// [`from_reflect`]: Self::from_reflect
/// [`DynamicStruct`]: crate::DynamicStruct
/// [`DynamicList`]: crate::DynamicList
fn take_from_reflect(reflect: Box<dyn Reflect>) -> Result<Self, Box<dyn Reflect>> {
match reflect.take::<Self>() {
Ok(value) => Ok(value),
Err(value) => match Self::from_reflect(value.as_ref()) {
None => Err(value),
Some(value) => Ok(value),
},
}
}
}
/// Type data that represents the [`FromReflect`] trait and allows it to be used dynamically.
///
/// `FromReflect` allows dynamic types (e.g. [`DynamicStruct`], [`DynamicEnum`], etc.) to be converted
/// to their full, concrete types. This is most important when it comes to deserialization where it isn't
/// guaranteed that every field exists when trying to construct the final output.
///
/// However, to do this, you normally need to specify the exact concrete type:
///
/// ```
/// # use bevy_reflect::{DynamicTupleStruct, FromReflect, Reflect};
/// #[derive(Reflect, PartialEq, Eq, Debug)]
/// struct Foo(#[reflect(default = "default_value")] usize);
///
/// fn default_value() -> usize { 123 }
///
/// let reflected = DynamicTupleStruct::default();
///
/// let concrete: Foo = <Foo as FromReflect>::from_reflect(&reflected).unwrap();
///
/// assert_eq!(Foo(123), concrete);
/// ```
///
/// In a dynamic context where the type might not be known at compile-time, this is nearly impossible to do.
/// That is why this type data struct exists— it allows us to construct the full type without knowing
/// what the actual type is.
///
/// # Example
///
/// ```
/// # use bevy_reflect::{DynamicTupleStruct, Reflect, ReflectFromReflect, Typed, TypeRegistry, TypePath};
/// # #[derive(Reflect, PartialEq, Eq, Debug)]
/// # struct Foo(#[reflect(default = "default_value")] usize);
/// # fn default_value() -> usize { 123 }
/// # let mut registry = TypeRegistry::new();
/// # registry.register::<Foo>();
///
/// let mut reflected = DynamicTupleStruct::default();
/// reflected.set_represented_type(Some(<Foo as Typed>::type_info()));
///
/// let registration = registry.get_with_type_path(<Foo as TypePath>::type_path()).unwrap();
/// let rfr = registration.data::<ReflectFromReflect>().unwrap();
///
/// let concrete: Box<dyn Reflect> = rfr.from_reflect(&reflected).unwrap();
///
/// assert_eq!(Foo(123), concrete.take::<Foo>().unwrap());
/// ```
///
/// [`DynamicStruct`]: crate::DynamicStruct
/// [`DynamicEnum`]: crate::DynamicEnum
#[derive(Clone)]
pub struct ReflectFromReflect {
from_reflect: fn(&dyn Reflect) -> Option<Box<dyn Reflect>>,
}
impl ReflectFromReflect {
/// Perform a [`FromReflect::from_reflect`] conversion on the given reflection object.
///
/// This will convert the object to a concrete type if it wasn't already, and return
/// the value as `Box<dyn Reflect>`.
#[allow(clippy::wrong_self_convention)]
pub fn from_reflect(&self, reflect_value: &dyn Reflect) -> Option<Box<dyn Reflect>> {
(self.from_reflect)(reflect_value)
}
}
impl<T: FromReflect> FromType<T> for ReflectFromReflect {
fn from_type() -> Self {
Self {
from_reflect: |reflect_value| {
T::from_reflect(reflect_value).map(|value| Box::new(value) as Box<dyn Reflect>)
},
}
}
}