LibCore+LibGUI: Add is<T>(CObject&) and to<T>(CObject&) helpers.

Author: https://github.com/awesomekling
Commit: 0c85d3dba9

LibCore/CObject.h

@@ -58,3 +58,20 @@ private:
     bool m_widget { false };
     Vector<CObject*> m_children;
 };
+
+template<typename T> inline bool is(const CObject&) { return false; }
+template<> inline bool is<CObject>(const CObject&) { return true; }
+
+template<typename T>
+inline T& to(CObject& object)
+{
+    ASSERT(is<T>(object));
+    return static_cast<T&>(object);
+}
+
+template<typename T>
+inline const T& to(const CObject& object)
+{
+    ASSERT(is<T>(object));
+    return static_cast<const T&>(object);
+}

LibGUI/GStackWidget.cpp

@@ -33,9 +33,9 @@ void GStackWidget::resize_event(GResizeEvent& event)
 
 void GStackWidget::child_event(CChildEvent& event)
 {
-    if (!event.child() || !event.child()->is_widget())
+    if (!event.child() || !is<GWidget>(*event.child()))
         return GWidget::child_event(event);
-    auto& child = static_cast<GWidget&>(*event.child());
+    auto& child = to<GWidget>(*event.child());
     if (event.type() == GEvent::ChildAdded) {
         if (!m_active_widget)
             set_active_widget(&child);
@@ -44,12 +44,10 @@ void GStackWidget::child_event(CChildEvent& event)
     } else if (event.type() == GEvent::ChildRemoved) {
         if (m_active_widget == &child) {
             GWidget* new_active_widget = nullptr;
-            for (auto* new_child : children()) {
+            for_each_child_widget([&] (auto& new_child) {
-                if (new_child->is_widget()) {
+                new_active_widget = &new_child;
-                    new_active_widget = static_cast<GWidget*>(new_child);
+                return IterationDecision::Abort;
-                    break;
+            });
-                }
-            }
             set_active_widget(new_active_widget);
         }
     }

LibGUI/GTabWidget.cpp

@@ -50,9 +50,9 @@ Rect GTabWidget::child_rect_for_size(const Size& size) const
 
 void GTabWidget::child_event(CChildEvent& event)
 {
-    if (!event.child() || !event.child()->is_widget())
+    if (!event.child() || !is<GWidget>(*event.child()))
         return GWidget::child_event(event);
-    auto& child = static_cast<GWidget&>(*event.child());
+    auto& child = to<GWidget>(*event.child());
     if (event.type() == GEvent::ChildAdded) {
         if (!m_active_widget)
             set_active_widget(&child);

LibGUI/GWidget.cpp

@@ -26,13 +26,13 @@ GWidget::~GWidget()
 void GWidget::child_event(CChildEvent& event)
 {
     if (event.type() == GEvent::ChildAdded) {
-        if (event.child() && event.child()->is_widget() && layout())
+        if (event.child() && is<GWidget>(*event.child()) && layout())
-            layout()->add_widget(static_cast<GWidget&>(*event.child()));
+            layout()->add_widget(to<GWidget>(*event.child()));
     }
     if (event.type() == GEvent::ChildRemoved) {
         if (layout()) {
-            if (event.child() && event.child()->is_widget())
+            if (event.child() && is<GWidget>(*event.child()))
-                layout()->remove_widget(static_cast<GWidget&>(*event.child()));
+                layout()->remove_widget(to<GWidget>(*event.child()));
             else
                 invalidate_layout();
         }
@@ -321,9 +321,9 @@ Rect GWidget::screen_relative_rect() const
 GWidget* GWidget::child_at(const Point& point) const
 {
     for (int i = children().size() - 1; i >= 0; --i) {
-        if (!children()[i]->is_widget())
+        if (!is<GWidget>(*children()[i]))
             continue;
-        auto& child = *(GWidget*)children()[i];
+        auto& child = to<GWidget>(*children()[i]);
         if (!child.is_visible())
             continue;
         if (child.relative_rect().contains(point))

LibGUI/GWidget.h

@@ -141,18 +141,8 @@ public:
 
     void set_window(GWindow*);
 
-    GWidget* parent_widget()
+    GWidget* parent_widget();
-    {
+    const GWidget* parent_widget() const;
-        if (parent() && parent()->is_widget())
-            return static_cast<GWidget*>(parent());
-        return nullptr;
-    }
-    const GWidget* parent_widget() const
-    {
-        if (parent() && parent()->is_widget())
-            return static_cast<const GWidget*>(parent());
-        return nullptr;
-    }
 
     void set_fill_with_background_color(bool b) { m_fill_with_background_color = b; }
     bool fill_with_background_color() const { return m_fill_with_background_color; }
@@ -189,8 +179,8 @@ public:
     void for_each_child_widget(Callback callback)
     {
         for_each_child([&] (auto& child) {
-            if (child.is_widget())
+            if (is<GWidget>(child))
-                return callback(static_cast<GWidget&>(child));
+                return callback(to<GWidget>(child));
             return IterationDecision::Continue;
         });
     }
@@ -233,3 +223,21 @@ private:
 
     HashMap<GShortcut, GAction*> m_local_shortcut_actions;
 };
+
+template<> inline bool is<GWidget>(const CObject& object)
+{
+    return object.is_widget();
+}
+
+inline GWidget* GWidget::parent_widget()
+{
+    if (parent() && is<GWidget>(*parent()))
+        return &to<GWidget>(*parent());
+    return nullptr;
+}
+inline const GWidget* GWidget::parent_widget() const
+{
+    if (parent() && is<GWidget>(*parent()))
+        return &to<const GWidget>(*parent());
+    return nullptr;
+}