WIP Add downcasting

crates/cxx-qt-gen/src/generator/rust/qobject.rs

@@ -118,7 +118,14 @@ impl GeneratedRustFragment {
                     unsafe fn upcast_ptr(this: *const Self) -> *const #base_qualified {
                         #upcast_fn_qualified(this)
                     }
+
+                    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+                        None //TODO! placeholder, use the right dynamic_cast function 
+                    }
                 }
+            },
+            quote! {
+                impl ::cxx_qt::Downcast for #struct_name {}
             }],
         };
         blocks

crates/cxx-qt-gen/test_outputs/inheritance.rs

@@ -89,7 +89,11 @@ impl ::cxx_qt::Upcast<inheritance::QAbstractItemModel> for inheritance::MyObject
     unsafe fn upcast_ptr(this: *const Self) -> *const inheritance::QAbstractItemModel {
         inheritance::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for inheritance::MyObject {}
 #[doc(hidden)]
 pub fn create_rs_MyObjectRust() -> std::boxed::Box<MyObjectRust> {
     std::boxed::Box::new(core::default::Default::default())

crates/cxx-qt-gen/test_outputs/invokables.rs

@@ -307,7 +307,11 @@ impl ::cxx_qt::Upcast<::cxx_qt::qobject::QObject> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::qobject::QObject {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for ffi::MyObject {}
 #[doc(hidden)]
 pub fn route_arguments_MyObject_0<'a>(
     arg0: i32,

crates/cxx-qt-gen/test_outputs/passthrough_and_naming.rs

@@ -612,7 +612,11 @@ impl ::cxx_qt::Upcast<ffi::QStringListModel> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ffi::QStringListModel {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for ffi::MyObject {}
 #[doc(hidden)]
 pub fn create_rs_MyObjectRust() -> std::boxed::Box<MyObjectRust> {
     std::boxed::Box::new(core::default::Default::default())
@@ -782,7 +786,11 @@ impl ::cxx_qt::Upcast<::cxx_qt::qobject::QObject> for ffi::SecondObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::qobject::QObject {
         ffi::cxx_qt_ffi_SecondObject_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for ffi::SecondObject {}
 #[doc(hidden)]
 pub fn create_rs_SecondObjectRust() -> std::boxed::Box<SecondObjectRust> {
     std::boxed::Box::new(core::default::Default::default())
@@ -806,7 +814,11 @@ impl ::cxx_qt::Upcast<::cxx_qt::qobject::QObject> for ffi::MyRustName {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::qobject::QObject {
         ffi::cxx_qt_ffi_MyCxxName_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for ffi::MyRustName {}
 #[doc(hidden)]
 pub fn create_rs_ThirdObjectRust() -> std::boxed::Box<ThirdObjectRust> {
     std::boxed::Box::new(core::default::Default::default())

crates/cxx-qt-gen/test_outputs/properties.rs

@@ -1051,7 +1051,11 @@ impl ::cxx_qt::Upcast<::cxx_qt::qobject::QObject> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::qobject::QObject {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for ffi::MyObject {}
 #[doc(hidden)]
 pub fn create_rs_MyObjectRust() -> std::boxed::Box<MyObjectRust> {
     std::boxed::Box::new(core::default::Default::default())

crates/cxx-qt-gen/test_outputs/qenum.rs

@@ -164,7 +164,11 @@ impl ::cxx_qt::Upcast<::cxx_qt::qobject::QObject> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::qobject::QObject {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for ffi::MyObject {}
 #[doc(hidden)]
 pub fn create_rs_MyObjectRust() -> std::boxed::Box<MyObjectRust> {
     std::boxed::Box::new(core::default::Default::default())
@@ -188,7 +192,11 @@ impl ::cxx_qt::Upcast<::cxx_qt::qobject::QObject> for ffi::MyRenamedObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::qobject::QObject {
         ffi::cxx_qt_ffi_CxxName_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for ffi::MyRenamedObject {}
 #[doc(hidden)]
 pub fn create_rs_InternalObject() -> std::boxed::Box<InternalObject> {
     std::boxed::Box::new(core::default::Default::default())

crates/cxx-qt-gen/test_outputs/signals.rs

@@ -442,7 +442,11 @@ impl ::cxx_qt::Upcast<::cxx_qt::qobject::QObject> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::qobject::QObject {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self> {
+        None
+    }
 }
+impl ::cxx_qt::Downcast for ffi::MyObject {}
 #[doc(hidden)]
 pub fn create_rs_MyObjectRust() -> std::boxed::Box<MyObjectRust> {
     std::boxed::Box::new(core::default::Default::default())

crates/cxx-qt/include/casting.h

@@ -15,4 +15,6 @@ upcastPtr(const Sub* sub)
   return static_cast<const Base*>(sub);
 }
 
+// TODO! add base_ptr downcasting function here
+
 }

crates/cxx-qt/src/lib.rs

@@ -132,6 +132,10 @@ pub trait Upcast<T> {
     /// Internal function, Should not be implemented manually
     unsafe fn upcast_ptr(this: *const Self) -> *const T;
 
+    #[doc(hidden)]
+    /// Internal function, Should not be implemented manually
+    unsafe fn from_base_ptr(base: *const T) -> Option<*const Self>;
+
     /// Upcast a reference to a reference to the base class
     fn upcast(&self) -> &T {
         let ptr = self as *const Self;
@@ -160,6 +164,14 @@ pub trait Upcast<T> {
     }
 }
 
+/// Trait for downcasting to a subclass, provided the subclass implements Upcast to this type
+pub trait Downcast: Sized {
+    /// Downcast to a subclass of this, given that the subclass upcasts to this type
+    fn downcast<Sub: Upcast<Self>>(&self) -> Option<&Sub> {
+        unsafe { Sub::from_base_ptr(self as *const Self).map(|sub| &*sub) }
+    }
+}
+
 /// This trait can be implemented on any [CxxQtType] to define a
 /// custom constructor in C++ for the QObject.
 ///