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

LibCore/CObject.h

@@ -58,3 +58,20 @@ class CObject : public Weakable<CObject> {
  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()) {
- if (new_child->is_widget()) {
- new_active_widget = static_cast<GWidget*>(new_child);
- break;
- }
- }
+ for_each_child_widget([&] (auto& new_child) {
+ new_active_widget = &new_child;
+ return IterationDecision::Abort;
+ });
  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())
- layout()->add_widget(static_cast<GWidget&>(*event.child()));
+ if (event.child() && is<GWidget>(*event.child()) && layout())
+ layout()->add_widget(to<GWidget>(*event.child()));
  }
  if (event.type() == GEvent::ChildRemoved) {
  if (layout()) {
- if (event.child() && event.child()->is_widget())
- layout()->remove_widget(static_cast<GWidget&>(*event.child()));
+ if (event.child() && is<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 @@ class GWidget : public CObject {
 
  void set_window(GWindow*);
 
- GWidget* parent_widget()
- {
- 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;
- }
+ GWidget* parent_widget();
+ const GWidget* parent_widget() const;
 
  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 @@ class GWidget : public CObject {
  void for_each_child_widget(Callback callback)
  {
  for_each_child([&] (auto& child) {
- if (child.is_widget())
- return callback(static_cast<GWidget&>(child));
+ if (is<GWidget>(child))
+ return callback(to<GWidget>(child));
  return IterationDecision::Continue;
  });
  }
@@ -233,3 +223,21 @@ class GWidget : public CObject {
 
  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;
+}