Allow to use `#[func(gd_self)]` with Interface methods. #1282

Yarwin · 2025-08-24T18:50:52Z

Adds #[func(gd_self)] to virtual methods.

Functions annotated with this attribute are being moved from Trait Impl to Inherent Impl and are registered accordingly. (I'm not sure if I they should be renamed as well – i.e. __godot_virtual_{virtual_method_name} instead of {virtual_method_name}.

Multiple callbacks are being handled by enum/wrapper/whatever which holds the inner instance; It has been done so to keep storage and whatnot isolated. Initially I wanted to return dereferenced value (wrapper.recv()) but compiler was throwing tantrum and demanding polluting everything with lifetimes which was ultra silly – thus a respectable impl Deref<Target = T> + use<'a, T> was used instead (I think it is better design choice anyway?). Unfortunately it requires doing some silly things with std::mem::replace.

Supports everything, but errors which pop out while trying to use #[gd_self] with methods that have other receiver than self are annoying. I think I'll just hardcode all such cases later (:roll_eyes:) (so far only callbacks are "shielded").

GodotRust · 2025-08-24T19:06:25Z

API docs are being generated and will be shortly available at: https://godot-rust.github.io/docs/gdext/pr-1282

Bromeon

Thanks a lot, this is a fantastic feature addition! 💪

Bromeon · 2025-08-25T12:16:03Z

godot-core/src/obj/traits.rs

+        type Recv: IntoVirtualMethodReceiver<Self>;
+        #[doc(hidden)]


Nitpick: empty line (in all places like this)

Bromeon · 2025-08-25T12:18:57Z

godot-core/src/storage/instance_storage.rs

+pub enum VirtualMethodReceiverInner<'a, T: GodotClass> {
+    /// &self.
+    SelfRecv(RefGuard<'a, T>),
+    /// &mut self.
+    SelfMutRecv(MutGuard<'a, T>),
+    /// this: Gd<Self>.
+    GdRecv(Gd<T>),
+    /// Blank.
+    Uninit,
+}


Should follow prior art with naming:

gdext/godot-macros/src/class/data_models/func.rs

Lines 182 to 188 in 4737427

#[derive(Copy, Clone, Eq, PartialEq, Debug)]

pub enum ReceiverType {

Ref,

Mut,

GdSelf,

Static,

}

The "Recv" is redundant with enum name "Receiver".

"Uninit" is not a valid state but a technical implementation detail needed for the swap idiom, right? Please add documentation, "blank" doesn't explain anything 😉

Also, why does it need to be pub if it's an inner type?

Bromeon · 2025-08-25T12:28:35Z

godot-core/src/storage/instance_storage.rs

+// Marker structs.
+// Used to extract proper type from storage and pass it to public API while defined as an associated item on the trait (`T::Recv::instance(storage)`).
+
+#[doc(hidden)]
+pub struct SelfRecv;
+#[doc(hidden)]
+pub struct SelfMutRecv;
+#[doc(hidden)]
+pub struct GdRecv;


You can make those enums, so they're uninhabitable (no instance can be created).

Naming see above, maybe to differ it from the enum values, you could use something like RecvRef/RecvMut/RecvGdSelf` or so...

Bromeon · 2025-08-25T12:30:32Z

godot-macros/src/class/data_models/func.rs

@@ -255,7 +255,12 @@ fn make_forwarding_closure(
    let before_method_call = match before_kind {
        BeforeKind::WithBefore | BeforeKind::OnlyBefore => {
            let before_method = format_ident!("__before_{}", method_name);
-            quote! { instance.#before_method(); }
+            if let ReceiverType::GdSelf = &signature_info.receiver_type {


Suggested change

if let ReceiverType::GdSelf = &signature_info.receiver_type {

if let ReceiverType::GdSelf = signature_info.receiver_type {

It's Copy, no?

Bromeon · 2025-08-25T12:33:47Z

godot-macros/src/lib.rs

+/// #[godot_api]
+/// impl INode for MyStruct {
+///     #[func(gd_self)]
+///     fn ready(this: Gd<Self>) {
+///         godot_print!("I'm ready!");
+///     }


This seems a bit out of place in the docs that introduce basic #[func]. Virtual methods with custom this should probably have their own section, and elaborate what motivates their need. There is no explanation about #[func(gd_self)] here, and since an attribute is required, we cannot make it seem the default.

Bromeon · 2025-08-25T12:36:29Z

itest/rust/src/object_tests/virtual_methods_test.rs

+    #[func(gd_self)]
+    fn set_property(mut this: Gd<Self>, _property: StringName, value: Variant) -> bool {
+        this.bind_mut().some_val = value.to();
+        !this.bind().some_val == 4


Do you mean != ?

This is bitwise negation...

Bromeon · 2025-08-25T12:37:04Z

itest/rust/src/object_tests/virtual_methods_test.rs

+
+    #[func(gd_self)]
+    fn property_get_revert(this: Gd<Self>, property: StringName) -> Option<Variant> {
+        Some(Self::get_property(this, property)?.to_variant())


Please avoid ? inside expressions, they're hard to see.

Instead, declare a variable, so ? is at the end of line.

Bromeon · 2025-08-25T12:37:42Z

itest/rust/src/object_tests/virtual_methods_test.rs

+    let mut obj = VirtualGdSelfTest::new_gd();
+    assert_eq!(GString::from("Gd<Self>"), obj.call("to_string", &[]).to());
+
+    let ret = obj.call("get", &["".to_variant()]).to();


Suggested change

let ret = obj.call("get", &["".to_variant()]).to();

let ret = obj.call("get", vslice[""]).to();

Bromeon · 2025-08-25T12:38:12Z

itest/rust/src/object_tests/virtual_methods_test.rs

+#[itest]
+fn test_gd_self_virtual_methods() {
+    let mut obj = VirtualGdSelfTest::new_gd();
+    assert_eq!(GString::from("Gd<Self>"), obj.call("to_string", &[]).to());


Assertions should always have actual, expected order.

For complex expressions, feel free to store the actual part in a variable.

Also below.

Oh, I see why I changed the order – for some reason type inference works only if we have assert_eq!(concrete, infered).

(I changed them anyway, I think actual, expected is a bit more readable)

Bromeon · 2025-08-25T13:00:49Z

godot-core/src/storage/instance_storage.rs

+    pub fn recv_gd(mut self) -> Gd<T> {
+        let mut out = VirtualMethodReceiverInner::Uninit;
+        std::mem::swap(&mut out, &mut self.inner);
+
+        let VirtualMethodReceiverInner::GdRecv(instance) = out else {
+            panic!("Tried to use Gd<T> receiver for method which doesn't accept it.")
+        };
+
+        instance
+    }
+
+    pub fn recv_self(mut self) -> impl Deref<Target = T> + use<'a, T> {
+        let mut out = VirtualMethodReceiverInner::Uninit;
+        std::mem::swap(&mut out, &mut self.inner);
+        let VirtualMethodReceiverInner::SelfRecv(instance) = out else {
+            panic!("Tried to use &self receiver for method which doesn't accept it.")
+        };
+
+        instance
+    }
+
+    pub fn recv_self_mut(mut self) -> impl DerefMut<Target = T> + use<'a, T> {
+        let mut out = VirtualMethodReceiverInner::Uninit;
+        std::mem::swap(&mut out, &mut self.inner);
+        let VirtualMethodReceiverInner::SelfMutRecv(instance) = out else {
+            panic!("Tried to use &mut self receiver for method which doesn't accept it.")
+        };
+
+        instance
+    }


You can probably use mem::replace here?

Also, I was thinking to outsource common code into function/macro, but there's barely any benefit.

There is however not much reason to do let else, since the "then" case is only instance -- so I'd use either regular if let or match.

Is the panic! actually an unreachable!, indicating an internal godot-rust bug? Or can users run into it?

Is the panic! actually an unreachable!, indicating an internal godot-rust bug? Or can users run into it?

all traits and virtual functions – which are written via macros – can be implemented manually, so theoretically it is possible 😄, albeit very unlikely.

(in other words – it is private albeit user-facing API, so I assume that it can be misused. I'm not sure if we won't use(/expose) it with builder as well (if I'll ever get myself to actually sit down and implement it 😄 ))

Yarwin added feature Adds functionality to the library c: core Core components c: register Register classes, functions and other symbols to GDScript labels Aug 24, 2025

Yarwin force-pushed the add-gd-self-receiver-to-virtual-methods branch 2 times, most recently from 45f3a97 to 137aefd Compare August 24, 2025 18:55

Yarwin force-pushed the add-gd-self-receiver-to-virtual-methods branch from 137aefd to 885c3fc Compare August 24, 2025 19:07

Bromeon removed the c: core Core components label Aug 24, 2025

Yarwin force-pushed the add-gd-self-receiver-to-virtual-methods branch 2 times, most recently from 9ce4368 to edd3d17 Compare August 25, 2025 07:03

Bromeon reviewed Aug 25, 2025

View reviewed changes

Allow to use #[func(gd_self)] with Interface methods.

47b59cb

Yarwin force-pushed the add-gd-self-receiver-to-virtual-methods branch from edd3d17 to 47b59cb Compare August 25, 2025 14:19

	#[derive(Copy, Clone, Eq, PartialEq, Debug)]
	pub enum ReceiverType {
	Ref,
	Mut,
	GdSelf,
	Static,
	}

	if let ReceiverType::GdSelf = &signature_info.receiver_type {
	if let ReceiverType::GdSelf = signature_info.receiver_type {

	let ret = obj.call("get", &["".to_variant()]).to();
	let ret = obj.call("get", vslice[""]).to();

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Allow to use #[func(gd_self)] with Interface methods. #1282

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Allow to use #[func(gd_self)] with Interface methods. #1282

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Allow to use `#[func(gd_self)]` with Interface methods. #1282

Allow to use `#[func(gd_self)]` with Interface methods. #1282

Yarwin commented Aug 24, 2025 •

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