Make Widget::diff mutable

examples/loupe/src/main.rs

@@ -87,8 +87,8 @@ mod loupe {
             self.content.as_widget().children()
         }
 
-        fn diff(&self, tree: &mut widget::Tree) {
-            self.content.as_widget().diff(tree);
+        fn diff(&mut self, tree: &mut widget::Tree) {
+            self.content.as_widget_mut().diff(tree);
         }
 
         fn size(&self) -> Size<Length> {

examples/toast/src/main.rs

@@ -314,7 +314,7 @@ mod toast {
                 .collect()
         }
 
-        fn diff(&self, tree: &mut Tree) {
+        fn diff(&mut self, tree: &mut Tree) {
             let instants = tree.state.downcast_mut::<Vec<Option<Instant>>>();
 
             // Invalidating removed instants to None allows us to remove
@@ -336,8 +336,8 @@ mod toast {
             }
 
             tree.diff_children(
-                &std::iter::once(&self.content)
-                    .chain(self.toasts.iter())
+                &mut std::iter::once(&mut self.content)
+                    .chain(self.toasts.iter_mut())
                     .collect::<Vec<_>>(),
             );
         }