Implement DynGd::null_arg()

Author: Bromeon

godot-core/src/meta/args/as_arg.rs

@@ -224,6 +224,42 @@ where
     }
 }
 
+// ----------------------------------------------------------------------------------------------------------------------------------------------
+// Null arguments
+
+/// Private struct for passing null arguments to optional object parameters.
+///
+/// This struct implements `AsArg` for both `Option<Gd<T>>` and `Option<DynGd<T, D>>`, allowing [`Gd::null_arg()`] and [`DynGd::null_arg()`]
+/// to share implementation.
+///
+/// Not public, as `impl AsArg<...>` is used by `null_arg()` methods.
+pub(crate) struct NullArg<T>(pub std::marker::PhantomData<*mut T>);
+
+impl<T> AsArg<Option<Gd<T>>> for NullArg<T>
+where
+    T: GodotClass,
+{
+    fn into_arg<'arg>(self) -> CowArg<'arg, Option<Gd<T>>>
+    where
+        Self: 'arg,
+    {
+        CowArg::Owned(None)
+    }
+}
+
+impl<T, D> AsArg<Option<DynGd<T, D>>> for NullArg<T>
+where
+    T: GodotClass,
+    D: ?Sized + 'static,
+{
+    fn into_arg<'arg>(self) -> CowArg<'arg, Option<DynGd<T, D>>>
+    where
+        Self: 'arg,
+    {
+        CowArg::Owned(None)
+    }
+}
+
 // ----------------------------------------------------------------------------------------------------------------------------------------------
 // Optional object (Gd + DynGd) impls
 

godot-core/src/meta/args/mod.rs

@@ -16,6 +16,7 @@ mod ref_arg;
 pub use as_arg::{
     owned_into_arg, ref_to_arg, ArgPassing, AsArg, ByObject, ByOption, ByRef, ByValue, ToArg,
 };
+
 // ----------------------------------------------------------------------------------------------------------------------------------------------
 // Internal APIs
 
@@ -29,6 +30,8 @@ pub(crate) use cow_arg::{CowArg, FfiArg};
 pub use object_arg::ObjectArg;
 pub use ref_arg::RefArg;
 
+pub(crate) use as_arg::NullArg;
+
 // #[doc(hidden)]
 // pub use cow_arg::*;
 //

godot-core/src/obj/dyn_gd.rs

@@ -403,6 +403,13 @@ where
     pub fn into_gd(self) -> Gd<T> {
         self.obj
     }
+
+    /// Represents `null` when passing a dynamic object argument to Godot.
+    ///
+    /// See [`Gd::null_arg()`]
+    pub fn null_arg() -> impl meta::AsArg<Option<DynGd<T, D>>> {
+        meta::NullArg(std::marker::PhantomData)
+    }
 }
 
 impl<T, D> DynGd<T, D>

godot-core/src/obj/gd.rs

@@ -816,22 +816,7 @@ where
     /// let mut shape: Gd<Node> = some_node();
     /// shape.set_owner(Gd::null_arg());
     pub fn null_arg() -> impl AsArg<Option<Gd<T>>> {
-        // Anonymous struct that creates None for optional object arguments.
-        struct NullGdArg<T>(std::marker::PhantomData<*mut T>);
-
-        impl<T> AsArg<Option<Gd<T>>> for NullGdArg<T>
-        where
-            T: GodotClass,
-        {
-            fn into_arg<'arg>(self) -> CowArg<'arg, Option<Gd<T>>>
-            where
-                Self: 'arg,
-            {
-                CowArg::Owned(None)
-            }
-        }
-
-        NullGdArg(std::marker::PhantomData)
+        meta::NullArg(std::marker::PhantomData)
     }
 }
 

itest/rust/src/object_tests/dyn_gd_test.rs

@@ -451,9 +451,9 @@ fn dyn_gd_as_arg() {
         Some(&refc_health),
         Some(&node_health),
         typed_none,
-        // Gd::null_arg(),
+        DynGd::null_arg(),
     ];
-    assert_eq!(opt_array.len(), 3);
+    assert_eq!(opt_array.len(), 4);
 
     let first = opt_array.at(0).expect("element 0 is Some");
     assert_eq!(first.dyn_bind().get_hitpoints(), 42);
@@ -464,6 +464,9 @@ fn dyn_gd_as_arg() {
     let third = opt_array.at(2);
     assert!(third.is_none(), "element 2 is None");
 
+    let fourth = opt_array.at(3);
+    assert!(fourth.is_none(), "element 3 is None (null_arg)");
+
     // Clean up manually managed objects.
     opt_array.at(1).unwrap().free();
 }