Fix comment.

CHANGELOG.md

@@ -35,6 +35,10 @@ current (development)
 - Bugfix: Fix cursor position in when in the last column. See #831.
 - Bugfix: Fix `ResizeableSplit` keyboard navigation. Fixed by #842.
 - Bugfix: Fix `Menu` focus. See #841
+- Feature: Add `ComponentBase::Index()`. This allows to get the index of a
+  component in its parent. See #932
+- Feature: Add `EntryState::index`. This allows to get the index of a menu entry.
+  See #932
 
 ### Dom
 - Feature: Add `hscroll_indicator`. It display an horizontal indicator

include/ftxui/component/component_base.hpp

@@ -44,7 +44,7 @@ class ComponentBase {
   ComponentBase* Parent() const;
   Component& ChildAt(size_t i);
   size_t ChildCount() const;
-  int IndexOf(ComponentBase* child) const;
+  int Index() const;
   void Add(Component children);
   void Detach();
   void DetachAllChildren();

src/ftxui/component/button.cpp

@@ -48,12 +48,8 @@ class ButtonBase : public ComponentBase, public ButtonOption {
     }
 
     auto focus_management = focused ? focus : active ? select : nothing;
-    const EntryState state = {
-        *label,
-        false,
-        active,
-        focused_or_hover,
-        -1,
+    const EntryState state{
+        *label, false, active, focused_or_hover, Index(),
     };
 
     auto element = (transform ? transform : DefaultTransform)  //

src/ftxui/component/checkbox.cpp

@@ -28,11 +28,7 @@ class CheckboxBase : public ComponentBase, public CheckboxOption {
     const bool is_active = Active();
     auto focus_management = is_focused ? focus : is_active ? select : nothing;
     auto entry_state = EntryState{
-        *label,
-        *checked,
-        is_active,
-        is_focused || hovered_,
-        -1,
+        *label, *checked, is_active, is_focused || hovered_, -1,
     };
     auto element = (transform ? transform : CheckboxOption::Simple().transform)(
         entry_state);

src/ftxui/component/component.cpp

@@ -51,16 +51,20 @@ size_t ComponentBase::ChildCount() const {
   return children_.size();
 }
 
-/// @brief Return index of child or -1 if not found.
+/// @brief Return index of the component in its parent. -1 if no parent.
 /// @ingroup component
-int ComponentBase::IndexOf(ComponentBase* child) const {
+int ComponentBase::Index() const {
+  if (parent_ == nullptr) {
+    return -1;
+  }
   int index = 0;
-  for (Component c : children_) {
-    if (&(*c) == child)
+  for (const Component& child : parent_->children_) {
+    if (child.get() == this) {
       return index;
+    }
     index++;
   }
-  return -1;
+  return -1;  // Not reached.
 }
 
 /// @brief Add a child.

src/ftxui/component/menu.cpp

@@ -123,11 +123,7 @@ class MenuBase : public ComponentBase, public MenuOption {
       const bool is_selected = (selected() == i);
 
       const EntryState state = {
-          entries[i],
-          false,
-          is_selected,
-          is_focused,
-          i,
+          entries[i], false, is_selected, is_focused, i,
       };
 
       auto focus_management = (selected_focus_ != i) ? nothing
@@ -626,12 +622,8 @@ Component MenuEntry(MenuEntryOption option) {
       const bool focused = Focused();
       UpdateAnimationTarget();
 
-      const EntryState state = {
-          label(),
-          false,
-          hovered_,
-          focused,
-          Parent()->IndexOf(this),
+      const EntryState state{
+          label(), false, hovered_, focused, Index(),
       };
 
       const Element element =

src/ftxui/component/menu_test.cpp

@@ -266,10 +266,8 @@ TEST(MenuTest, MenuEntryIndex) {
   menu->OnEvent(Event::ArrowDown);
   menu->OnEvent(Event::ArrowDown);
   menu->OnEvent(Event::Return);
-  for(int idx = 0; idx < menu->ChildCount(); idx++)
-  {
-    auto child = menu->ChildAt(idx);
-    EXPECT_EQ(menu->IndexOf(&(*child)), idx);  
+  for (int index = 0; index < menu->ChildCount(); index++) {
+    EXPECT_EQ(menu->ChildAt(index)->Index(), index);
   }
 }
 

src/ftxui/component/radiobox.cpp

@@ -40,11 +40,7 @@ class RadioboxBase : public ComponentBase, public RadioboxOption {
                               : is_menu_focused ? focus
                                                 : select;
       auto state = EntryState{
-          entries[i],
-          selected() == i,
-          is_selected,
-          is_focused,
-          i,
+          entries[i], selected() == i, is_selected, is_focused, i,
       };
       auto element =
           (transform ? transform : RadioboxOption::Simple().transform)(state);