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bevy_reflect: Added get_boxed method to reflect_trait (#4120)

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# Objective

Allow `Box<dyn Reflect>` to be converted into a `Box<dyn MyTrait>` using the `#[reflect_trait]` macro. The other methods `get` and `get_mut` only provide a reference to the reflected object.

## Solution

Add a `get_boxed` method to the `Reflect***` struct generated by the `#[reflect_trait]` macro. This method takes in a `Box<dyn Reflect>` and returns a `Box<dyn MyTrait>`.


Co-authored-by: MrGVSV <49806985+MrGVSV@users.noreply.github.com>
This commit is contained in:
Gino Valente 2022-05-20 13:31:49 +00:00
parent 7cb4d3cb43
commit 3a93b677a1
1 changed files with 35 additions and 0 deletions
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35
crates/bevy_reflect/bevy_reflect_derive/src/trait_reflection.rs
View file

@ -21,6 +21,10 @@ impl Parse for TraitInfo {
}
}
/// A trait attribute macro that allows a reflected type to be downcast to a trait object.
///
/// This generates a struct that takes the form `ReflectMyTrait`. An instance of this struct can then be
/// used to perform the conversion.
pub(crate) fn reflect_trait(_args: &TokenStream, input: TokenStream) -> TokenStream {
let trait_info = parse_macro_input!(input as TraitInfo);
let item_trait = &trait_info.item_trait;
@ -28,23 +32,51 @@ pub(crate) fn reflect_trait(_args: &TokenStream, input: TokenStream) -> TokenStr
let trait_vis = &item_trait.vis;
let reflect_trait_ident = crate::utility::get_reflect_ident(&item_trait.ident.to_string());
let bevy_reflect_path = BevyManifest::default().get_path("bevy_reflect");
let struct_doc = format!(
" A type generated by the #[reflect_trait] macro for the `{}` trait.\n\n This allows casting from `dyn Reflect` to `dyn {}`.",
trait_ident,
trait_ident
);
let get_doc = format!(
" Downcast a `&dyn Reflect` type to `&dyn {}`.\n\n If the type cannot be downcast, `None` is returned.",
trait_ident,
);
let get_mut_doc = format!(
" Downcast a `&mut dyn Reflect` type to `&mut dyn {}`.\n\n If the type cannot be downcast, `None` is returned.",
trait_ident,
);
let get_box_doc = format!(
" Downcast a `Box<dyn Reflect>` type to `Box<dyn {}>`.\n\n If the type cannot be downcast, this will return `Err(Box<dyn Reflect>)`.",
trait_ident,
);
TokenStream::from(quote! {
#item_trait
#[doc = #struct_doc]
#[derive(Clone)]
#trait_vis struct #reflect_trait_ident {
get_func: fn(&dyn #bevy_reflect_path::Reflect) -> Option<&dyn #trait_ident>,
get_mut_func: fn(&mut dyn #bevy_reflect_path::Reflect) -> Option<&mut dyn #trait_ident>,
get_boxed_func: fn(Box<dyn #bevy_reflect_path::Reflect>) -> Result<Box<dyn #trait_ident>, Box<dyn #bevy_reflect_path::Reflect>>,
}
impl #reflect_trait_ident {
#[doc = #get_doc]
pub fn get<'a>(&self, reflect_value: &'a dyn #bevy_reflect_path::Reflect) -> Option<&'a dyn #trait_ident> {
(self.get_func)(reflect_value)
}
#[doc = #get_mut_doc]
pub fn get_mut<'a>(&self, reflect_value: &'a mut dyn #bevy_reflect_path::Reflect) -> Option<&'a mut dyn #trait_ident> {
(self.get_mut_func)(reflect_value)
}
#[doc = #get_box_doc]
pub fn get_boxed(&self, reflect_value: Box<dyn #bevy_reflect_path::Reflect>) -> Result<Box<dyn #trait_ident>, Box<dyn #bevy_reflect_path::Reflect>> {
(self.get_boxed_func)(reflect_value)
}
}
impl<T: #trait_ident + #bevy_reflect_path::Reflect> #bevy_reflect_path::FromType<T> for #reflect_trait_ident {
@ -55,6 +87,9 @@ pub(crate) fn reflect_trait(_args: &TokenStream, input: TokenStream) -> TokenStr
},
get_mut_func: |reflect_value| {
reflect_value.downcast_mut::<T>().map(|value| value as &mut dyn #trait_ident)
},
get_boxed_func: |reflect_value| {
reflect_value.downcast::<T>().map(|value| value as Box<dyn #trait_ident>)
}
}
}