Allows components to remove a child or access to children in general (#152)

Allows components to remove a child or access to children in general.

Co-authored-by: Felix Heitmann <fheitmann@se-gpu-03.intern.plath.de>
Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

src/ftxui/component/component.cpp

@@ -1,4 +1,6 @@
+#include <stddef.h>   // for size_t
 #include <algorithm>  // for find_if, max
+#include <cassert>    // for assert
 #include <iterator>   // for begin, end
 #include <utility>    // for move
 
@@ -24,7 +26,6 @@ ComponentBase::~ComponentBase() {
 }
 
 /// @brief Return the parent ComponentBase, or nul if any.
-/// @see Attach
 /// @see Detach
 /// @see Parent
 /// @ingroup component
@@ -32,7 +33,20 @@ ComponentBase* ComponentBase::Parent() {
   return parent_;
 }
 
-/// @brief Add a children.
+/// @brief Access the child at index `i`.
+/// @ingroup component
+Component& ComponentBase::ChildAt(size_t i) {
+  assert(i < ChildCount());
+  return children_[i];
+}
+
+/// @brief Returns the number of children.
+/// @ingroup component
+size_t ComponentBase::ChildCount() const {
+  return children_.size();
+}
+
+/// @brief Add a child.
 /// @@param child The child to be attached.
 /// @ingroup component
 void ComponentBase::Add(Component child) {
@@ -41,6 +55,29 @@ void ComponentBase::Add(Component child) {
   children_.push_back(std::move(child));
 }
 
+/// @brief Detach this child from its parent.
+/// @see Detach
+/// @see Parent
+/// @ingroup component
+void ComponentBase::Detach() {
+  if (!parent_)
+    return;
+  auto it = std::find_if(std::begin(parent_->children_),  //
+                         std::end(parent_->children_),    //
+                         [this](const Component& that) {  //
+                           return this == that.get();
+                         });
+  parent_->children_.erase(it);
+  parent_ = nullptr;
+}
+
+/// @brief Remove all children.
+/// @ingroup component
+void ComponentBase::DetachAllChildren() {
+  while (!children_.empty())
+    children_[0]->Detach();
+}
+
 /// @brief Draw the component.
 /// Build a ftxui::Element to be drawn on the ftxi::Screen representing this
 /// ftxui::ComponentBase.
@@ -129,23 +166,6 @@ CapturedMouse ComponentBase::CaptureMouse(const Event& event) {
   return event.screen_->CaptureMouse();
 }
 
-/// @brief Detach this children from its parent.
-/// @see Attach
-/// @see Detach
-/// @see Parent
-/// @ingroup component
-void ComponentBase::Detach() {
-  if (!parent_)
-    return;
-  auto it = std::find_if(std::begin(parent_->children_),  //
-                         std::end(parent_->children_),    //
-                         [this](const Component& that) {  //
-                           return this == that.get();
-                         });
-  parent_->children_.erase(it);
-  parent_ = nullptr;
-}
-
 }  // namespace ftxui
 
 // Copyright 2020 Arthur Sonzogni. All rights reserved.