Gd::try_cast() now returns Err(self) instead of None on failure

Author: Bromeon

godot-core/src/engine/mod.rs

@@ -59,7 +59,7 @@ impl PackedSceneExt for PackedScene {
     where
         T: Inherits<Node>,
     {
-        self.instantiate().and_then(|gd| gd.try_cast::<T>())
+        self.instantiate().and_then(|gd| gd.try_cast::<T>().ok())
     }
 }
 
@@ -102,7 +102,7 @@ impl NodeExt for Node {
 
         // TODO differentiate errors (not found, bad type) with Result
         self.get_node_or_null(path)
-            .and_then(|node| node.try_cast::<T>())
+            .and_then(|node| node.try_cast::<T>().ok())
     }
 }
 
@@ -252,5 +252,5 @@ where
         .load_ex(path.clone())
         .type_hint(T::class_name().to_godot_string())
         .done() // TODO unclone
-        .and_then(|res| res.try_cast::<T>())
+        .and_then(|res| res.try_cast::<T>().ok())
 }

godot-core/src/obj/gd.rs

@@ -308,12 +308,12 @@ impl<T: GodotClass> Gd<T> {
     /// If `T`'s dynamic type is not `Derived` or one of its subclasses, `None` is returned
     /// and the reference is dropped. Otherwise, `Some` is returned and the ownership is moved
     /// to the returned value.
-    // TODO consider Result<Gd<Derived>, Self> so that user can still use original object (e.g. to free if manual)
-    pub fn try_cast<Derived>(self) -> Option<Gd<Derived>>
+    pub fn try_cast<Derived>(self) -> Result<Gd<Derived>, Self>
     where
         Derived: GodotClass + Inherits<T>,
     {
-        self.owned_cast().ok()
+        // Separate method due to more restrictive bounds.
+        self.owned_cast()
     }
 
     /// ⚠️ **Downcast:** convert into a smart pointer to a derived class. Panics on error.

itest/rust/src/object_tests/object_test.rs

@@ -552,7 +552,7 @@ fn object_reject_invalid_downcast() {
     let instance = Gd::from_object(CustomClassA {});
     let object = instance.upcast::<Object>();
 
-    assert!(object.try_cast::<CustomClassB>().is_none());
+    assert!(object.try_cast::<CustomClassB>().is_err());
 }
 
 #[itest]
@@ -577,11 +577,12 @@ fn object_engine_downcast_reflexive() {
 #[itest]
 fn object_engine_bad_downcast() {
     let object: Gd<Object> = Object::new_alloc();
-    let free_ref = object.clone();
-    let node3d: Option<Gd<Node3D>> = object.try_cast::<Node3D>();
+    let object2 = object.clone();
 
-    assert!(node3d.is_none());
-    free_ref.free();
+    let node3d: Result<Gd<Node3D>, Gd<Object>> = object.try_cast::<Node3D>();
+
+    assert_eq!(node3d, Err(object2.clone()));
+    object2.free();
 }
 
 #[itest]
@@ -665,9 +666,11 @@ fn object_user_downcast() {
 fn object_user_bad_downcast() {
     let obj = user_refc_instance();
     let object = obj.upcast::<Object>();
-    let node3d: Option<Gd<Node>> = object.try_cast::<Node>();
+    let object2 = object.clone();
+
+    let node3d: Result<Gd<Node>, Gd<Object>> = object.try_cast::<Node>();
 
-    assert!(node3d.is_none());
+    assert_eq!(node3d, Err(object2));
 }
 
 #[itest]

itest/rust/src/object_tests/virtual_methods_test.rs

@@ -376,7 +376,7 @@ fn test_format_loader(_test_context: &TestContext) {
         .cache_mode(CacheMode::CACHE_MODE_IGNORE)
         .done()
         .unwrap();
-    assert!(resource.try_cast::<BoxMesh>().is_some());
+    assert!(resource.try_cast::<BoxMesh>().is_ok());
 
     loader.remove_resource_format_loader(format_loader.upcast());
 }