Add subclass support for Fixed

src/subclass/fixed.rs

@@ -0,0 +1,17 @@
+// Copyright 2020, The Gtk-rs Project Developers.
+// See the COPYRIGHT file at the top-level directory of this distribution.
+// Licensed under the MIT license, see the LICENSE file or <http://opensource.org/licenses/MIT>
+
+use glib::subclass::prelude::*;
+
+use super::container::ContainerImpl;
+use ContainerClass;
+use FixedClass;
+
+pub trait FixedImpl: ContainerImpl + 'static {}
+
+unsafe impl<T: ObjectSubclass + FixedImpl> IsSubclassable<T> for FixedClass {
+    fn override_vfuncs(&mut self) {
+        <ContainerClass as IsSubclassable<T>>::override_vfuncs(self);
+    }
+}

src/subclass/mod.rs

@@ -19,6 +19,7 @@ pub mod container;
 pub mod dialog;
 pub mod drawing_area;
 pub mod event_box;
+pub mod fixed;
 pub mod header_bar;
 pub mod icon_view;
 pub mod stack;
@@ -43,6 +44,7 @@ pub mod prelude {
     pub use super::dialog::DialogImpl;
     pub use super::drawing_area::DrawingAreaImpl;
     pub use super::event_box::EventBoxImpl;
+    pub use super::fixed::FixedImpl;
     pub use super::header_bar::HeaderBarImpl;
     pub use super::icon_view::IconViewImpl;
     pub use super::stack::StackImpl;