Improved impl_cast

impl_cast/src/lib.rs

@@ -90,6 +90,26 @@ pub fn device(attr: TokenStream, item: TokenStream) -> TokenStream {
         .iter()
         .map(|device_trait| {
             quote! {
+                // Default impl
+                impl<T> #name<dyn #device_trait> for T
+                where
+                    T: #interface_ident + 'static,
+                {
+                    default fn consume(self: Box<Self>) -> Option<Box<dyn #device_trait>> {
+                        None
+                    }
+
+                    default fn cast(&self) -> Option<&(dyn #device_trait + 'static)> {
+                        None
+                    }
+
+                    default fn cast_mut(&mut self) -> Option<&mut (dyn #device_trait + 'static)> {
+                        None
+                    }
+                }
+
+                // Specialization, should not cause any unsoundness as we dispatch based on
+                // #device_trait
                 impl<T> #name<dyn #device_trait> for T
                 where
                     T: #interface_ident + #device_trait + 'static,
@@ -106,23 +126,6 @@ pub fn device(attr: TokenStream, item: TokenStream) -> TokenStream {
                         Some(self)
                     }
                 }
-
-                impl<T> #name<dyn #device_trait> for T
-                    where
-                        T: #interface_ident + ?Sized,
-                    {
-                        default fn consume(self: Box<Self>) -> Option<Box<dyn #device_trait>> {
-                            None
-                        }
-
-                        default fn cast(&self) -> Option<&(dyn #device_trait + 'static)> {
-                            None
-                        }
-
-                        default fn cast_mut(&mut self) -> Option<&mut (dyn #device_trait + 'static)> {
-                            None
-                        }
-                    }
             }
         })
         .fold(quote! {}, |acc, x| {
@@ -149,7 +152,7 @@ pub fn device_trait(_attr: TokenStream, item: TokenStream) -> TokenStream {
     let mut interface: ItemTrait = parse_macro_input!(item);
 
     interface.supertraits.push(TypeParamBound::Verbatim(quote! {
-        ::core::marker::Sync + ::core::marker::Send + 'static
+        ::core::marker::Sync + ::core::marker::Send
     }));
 
     #[cfg(feature = "debug")]