Add QtObject trait with basic as_ methods

Author: BenFordTytherington

crates/cxx-qt/src/lib.rs

@@ -9,6 +9,7 @@
 //!
 //! See the [book](https://kdab.github.io/cxx-qt/book/) for more information.
 
+use std::pin::Pin;
 use std::{fs::File, io::Write, path::Path};
 
 #[doc(hidden)]
@@ -125,6 +126,27 @@ pub use threading::{CxxQtThread, ThreadingQueueError};
 #[doc(hidden)]
 pub use static_assertions;
 
+/// This trait provides wrappers for objects which are QObjects or can be turned into a [QObject].
+/// It is automatically implemented for any types which implement [Upcast] to a [QObject].
+pub trait AsObject {
+    /// Cast self reference into a [QObject] reference
+    fn as_qobject(&self) -> &QObject;
+
+    /// Cast pinned mutable reference into a pinned mutable [QObject] reference
+    fn as_qobject_mut(self: Pin<&mut Self>) -> Pin<&mut QObject>;
+}
+
+impl<T: casting::Upcast<QObject>> AsObject for T {
+    fn as_qobject(&self) -> &QObject {
+        self.upcast()
+    }
+
+
+    fn as_qobject_mut(self: Pin<&mut Self>) -> Pin<&mut QObject> {
+        self.upcast_pin()
+    }
+}
+
 /// This trait is automatically implemented for all QObject types generated by CXX-Qt.
 /// It provides information about the inner Rust struct that is wrapped by the QObject, as well as the methods
 /// that Cxx-Qt will generate for the QObject.