1 files changed, 42 insertions, 0 deletions
diff --git a/engine-macros/src/reflection/default_value.rs b/engine-macros/src/reflection/default_value.rs
new file mode 100644
index 0000000..567c3b1
--- /dev/null
+++ b/engine-macros/src/reflection/default_value.rs
@@ -0,0 +1,42 @@
+use quote::quote;
+
+pub fn gen_get_default_value_fn(
+    type_ident: &proc_macro2::Ident,
+    type_generics: &syn::TypeGenerics,
+) -> proc_macro2::TokenStream
+{
+    quote! {
+        struct SpecializationTarget<T>(std::marker::PhantomData<T>);
+
+        trait HasDefaultValue
+        {
+            fn default_value_fn(&self) -> Option<fn() -> Box<dyn std::any::Any>>;
+        }
+
+        trait NoDefaultValue
+        {
+            fn default_value_fn(&self) -> Option<fn() -> Box<dyn std::any::Any>>;
+        }
+
+        impl<T> NoDefaultValue for &SpecializationTarget<T>
+        {
+            fn default_value_fn(&self) -> Option<fn() -> Box<dyn std::any::Any>>
+            {
+                None
+            }
+        }
+
+        impl<T> HasDefaultValue for SpecializationTarget<T>
+        where
+            T: std::default::Default + 'static
+        {
+            fn default_value_fn(&self) -> Option<fn() -> Box<dyn std::any::Any>>
+            {
+                Some(|| Box::new(T::default()))
+            }
+        }
+
+        (&SpecializationTarget::<#type_ident #type_generics>(std::marker::PhantomData))
+            .default_value_fn()
+    }
+}