...

11 files changed, 47 insertions, 43 deletions

diff --git a/.vscode/settings.json b/.vscode/settings.json
index c7947909..1de11236 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -65,6 +65,7 @@
     "xlocmon": "cpp",
     "xloctime": "cpp",
     "string_view": "cpp",
-    "cassert": "cpp"
+    "cassert": "cpp",
+    "gsl_util": "cpp"
   }
 }
diff --git a/include/cru/common/base.hpp b/include/cru/common/base.hpp
index daee971f..20dd811d 100644
--- a/include/cru/common/base.hpp
+++ b/include/cru/common/base.hpp
@@ -42,4 +42,6 @@ struct Interface {
 [[noreturn]] inline void UnreachableCode() {
   throw std::runtime_error("Unreachable code.");
 }
+
+using Index = gsl::index;
 }  // namespace cru
diff --git a/include/cru/ui/controls/flex_layout.hpp b/include/cru/ui/controls/flex_layout.hpp
index 52eaec75..ab08a80b 100644
--- a/include/cru/ui/controls/flex_layout.hpp
+++ b/include/cru/ui/controls/flex_layout.hpp
@@ -32,8 +32,8 @@ class FlexLayout : public LayoutControl {
   void SetChildLayoutData(Control* control, const FlexChildLayoutData& data);
 
  protected:
-  void OnAddChild(Control* child, int position) override;
-  void OnRemoveChild(Control* child, int position) override;
+  void OnAddChild(Control* child, Index position) override;
+  void OnRemoveChild(Control* child, Index position) override;
 
  private:
   std::shared_ptr<render::FlexLayoutRenderObject> render_object_;
diff --git a/include/cru/ui/controls/stack_layout.hpp b/include/cru/ui/controls/stack_layout.hpp
index 93861c19..20da0e82 100644
--- a/include/cru/ui/controls/stack_layout.hpp
+++ b/include/cru/ui/controls/stack_layout.hpp
@@ -22,8 +22,8 @@ class StackLayout : public LayoutControl {
   render::RenderObject* GetRenderObject() const override;
 
  protected:
-  void OnAddChild(Control* child, int position) override;
-  void OnRemoveChild(Control* child, int position) override;
+  void OnAddChild(Control* child, Index position) override;
+  void OnRemoveChild(Control* child, Index position) override;
 
  private:
   std::shared_ptr<render::StackLayoutRenderObject> render_object_;
diff --git a/include/cru/ui/layout_control.hpp b/include/cru/ui/layout_control.hpp
index 187f0e0d..e1856403 100644
--- a/include/cru/ui/layout_control.hpp
+++ b/include/cru/ui/layout_control.hpp
@@ -17,13 +17,13 @@ class LayoutControl : public Control {
     return children_;
   }
 
-  void AddChild(Control* control, int position);
+  void AddChild(Control* control, Index position);
 
-  void RemoveChild(int position);
+  void RemoveChild(Index position);
 
  protected:
-  virtual void OnAddChild(Control* child, int position);
-  virtual void OnRemoveChild(Control* child, int position);
+  virtual void OnAddChild(Control* child, Index position);
+  virtual void OnRemoveChild(Control* child, Index position);
 
  private:
   std::vector<Control*> children_;
diff --git a/include/cru/ui/render/layout_render_object.hpp b/include/cru/ui/render/layout_render_object.hpp
index 8700b8ba..5c4c9c5c 100644
--- a/include/cru/ui/render/layout_render_object.hpp
+++ b/include/cru/ui/render/layout_render_object.hpp
@@ -18,9 +18,9 @@ class LayoutRenderObject : public RenderObject {
 
   ~LayoutRenderObject() override = default;
 
-  ChildLayoutData* GetChildLayoutData(int position) {
+  ChildLayoutData* GetChildLayoutData(Index position) {
     Expects(position >= 0 &&
-           position < static_cast<int>(child_layout_data_.size()));
+            position < static_cast<Index>(child_layout_data_.size()));
     return &child_layout_data_[position];
   }
 
@@ -29,8 +29,8 @@ class LayoutRenderObject : public RenderObject {
   RenderObject* HitTest(const Point& point) override;
 
  protected:
-  void OnAddChild(RenderObject* new_child, int position) override;
-  void OnRemoveChild(RenderObject* removed_child, int position) override;
+  void OnAddChild(RenderObject* new_child, Index position) override;
+  void OnRemoveChild(RenderObject* removed_child, Index position) override;
 
  private:
   std::vector<ChildLayoutData> child_layout_data_{};
@@ -72,7 +72,7 @@ RenderObject* LayoutRenderObject<TChildLayoutData>::HitTest(
 
 template <typename TChildLayoutData>
 void LayoutRenderObject<TChildLayoutData>::OnAddChild(RenderObject* new_child,
-                                                      int position) {
+                                                      const Index position) {
   CRU_UNUSED(new_child)
 
   child_layout_data_.emplace(child_layout_data_.cbegin() + position);
@@ -80,7 +80,7 @@ void LayoutRenderObject<TChildLayoutData>::OnAddChild(RenderObject* new_child,
 
 template <typename TChildLayoutData>
 void LayoutRenderObject<TChildLayoutData>::OnRemoveChild(
-    RenderObject* removed_child, int position) {
+    RenderObject* removed_child, const Index position) {
   CRU_UNUSED(removed_child)
 
   child_layout_data_.erase(child_layout_data_.cbegin() + position);
diff --git a/include/cru/ui/render/render_object.hpp b/include/cru/ui/render/render_object.hpp
index ca31386a..33ef3d1a 100644
--- a/include/cru/ui/render/render_object.hpp
+++ b/include/cru/ui/render/render_object.hpp
@@ -53,9 +53,9 @@ class RenderObject : public Object {
   RenderObject* GetParent() const { return parent_; }
 
   const std::vector<RenderObject*>& GetChildren() const { return children_; }
-  int GetChildCount() const { return static_cast<int>(children_.size()); }
-  void AddChild(RenderObject* render_object, int position);
-  void RemoveChild(int position);
+  Index GetChildCount() const { return static_cast<Index>(children_.size()); }
+  void AddChild(RenderObject* render_object, Index position);
+  void RemoveChild(Index position);
 
   Point GetOffset() const { return offset_; }
   void SetOffset(const Point& offset) { offset_ = offset; }
@@ -99,9 +99,9 @@ class RenderObject : public Object {
                                RenderObject* new_parent);
 
   // default is to invalidate both layout and paint
-  virtual void OnAddChild(RenderObject* new_child, int position);
+  virtual void OnAddChild(RenderObject* new_child, Index position);
   // default is to invalidate both layout and paint
-  virtual void OnRemoveChild(RenderObject* removed_child, int position);
+  virtual void OnRemoveChild(RenderObject* removed_child, Index position);
 
   virtual void OnMeasureCore(const Size& available_size);
   virtual void OnLayoutCore(const Rect& rect);
diff --git a/src/ui/controls/flex_layout.cpp b/src/ui/controls/flex_layout.cpp
index c881b6f1..5412164a 100644
--- a/src/ui/controls/flex_layout.cpp
+++ b/src/ui/controls/flex_layout.cpp
@@ -59,11 +59,11 @@ void FlexLayout::SetFlexDirection(FlexDirection direction) {
   render_object_->SetFlexDirection(direction);
 }
 
-void FlexLayout::OnAddChild(Control* child, int position) {
+void FlexLayout::OnAddChild(Control* child, const Index position) {
   render_object_->AddChild(child->GetRenderObject(), position);
 }
 
-void FlexLayout::OnRemoveChild(Control* child, int position) {
+void FlexLayout::OnRemoveChild(Control* child, const Index position) {
   CRU_UNUSED(child)
 
   render_object_->RemoveChild(position);
diff --git a/src/ui/controls/stack_layout.cpp b/src/ui/controls/stack_layout.cpp
index b9abb510..47511f33 100644
--- a/src/ui/controls/stack_layout.cpp
+++ b/src/ui/controls/stack_layout.cpp
@@ -15,11 +15,11 @@ render::RenderObject* StackLayout::GetRenderObject() const {
   return render_object_.get();
 }
 
-void StackLayout::OnAddChild(Control* child, int position) {
+void StackLayout::OnAddChild(Control* child, const Index position) {
   render_object_->AddChild(child->GetRenderObject(), position);
 }
 
-void StackLayout::OnRemoveChild(Control* child, int position) {
+void StackLayout::OnRemoveChild(Control* child, const Index position) {
   CRU_UNUSED(child)
 
   render_object_->RemoveChild(position);
diff --git a/src/ui/layout_control.cpp b/src/ui/layout_control.cpp
index cb71da30..90a825ff 100644
--- a/src/ui/layout_control.cpp
+++ b/src/ui/layout_control.cpp
@@ -7,13 +7,14 @@ LayoutControl::~LayoutControl() {
   for (const auto child : children_) delete child;
 }
 
-void LayoutControl::AddChild(Control* control, const int position) {
-  Expects(control->GetParent() == nullptr);  // The control already has a parent.
+void LayoutControl::AddChild(Control* control, const Index position) {
+  Expects(control->GetParent() ==
+          nullptr);  // The control already has a parent.
   Expects(!dynamic_cast<Window*>(control));  // Can't add a window as child.
-  Expects(position >= 0 ||
-         position <=
-             static_cast<int>(
-                 this->children_.size()));  // The position is out of range.
+  Expects(position >= 0);
+  Expects(position <=
+          static_cast<Index>(
+              this->children_.size()));  // The position is out of range.
 
   children_.insert(this->children_.cbegin() + position, control);
 
@@ -23,11 +24,11 @@ void LayoutControl::AddChild(Control* control, const int position) {
   OnAddChild(control, position);
 }
 
-void LayoutControl::RemoveChild(const int position) {
-  Expects(position >= 0 &&
-         position <
-             static_cast<int>(
-                 this->children_.size()));  // The position is out of range.
+void LayoutControl::RemoveChild(const Index position) {
+  Expects(position >= 0);
+  Expects(position <
+          static_cast<Index>(
+              this->children_.size()));  // The position is out of range.
 
   const auto i = children_.cbegin() + position;
   const auto child = *i;
@@ -40,12 +41,12 @@ void LayoutControl::RemoveChild(const int position) {
   OnRemoveChild(child, position);
 }
 
-void LayoutControl::OnAddChild(Control* child, int position) {
+void LayoutControl::OnAddChild(Control* child, const Index position) {
   CRU_UNUSED(child)
   CRU_UNUSED(position)
 }
 
-void LayoutControl::OnRemoveChild(Control* child, int position) {
+void LayoutControl::OnRemoveChild(Control* child, const Index position) {
   CRU_UNUSED(child)
   CRU_UNUSED(position)
 }
diff --git a/src/ui/render/render_object.cpp b/src/ui/render/render_object.cpp
index c1b1b19b..e329d150 100644
--- a/src/ui/render/render_object.cpp
+++ b/src/ui/render/render_object.cpp
@@ -5,7 +5,7 @@
 #include <algorithm>
 
 namespace cru::ui::render {
-void RenderObject::AddChild(RenderObject* render_object, const int position) {
+void RenderObject::AddChild(RenderObject* render_object, const Index position) {
   Expects(child_mode_ != ChildMode::None);
   Expects(!(child_mode_ == ChildMode::Single && children_.size() > 0));
 
@@ -14,7 +14,7 @@ void RenderObject::AddChild(RenderObject* render_object, const int position) {
   Expects(position >= 0);  // Position index is less than 0.
   Expects(
       position <=
-      static_cast<int>(children_.size()));  // Position index is out of bound.
+      static_cast<Index>(children_.size()));  // Position index is out of bound.
 
   children_.insert(children_.cbegin() + position, render_object);
   render_object->SetParent(this);
@@ -22,9 +22,9 @@ void RenderObject::AddChild(RenderObject* render_object, const int position) {
   OnAddChild(render_object, position);
 }
 
-void RenderObject::RemoveChild(const int position) {
+void RenderObject::RemoveChild(const Index position) {
   Expects(position >= 0);  // Position index is less than 0.
-  Expects(position < static_cast<int>(
+  Expects(position < static_cast<Index>(
                          children_.size()));  // Position index is out of bound.
 
   const auto i = children_.cbegin() + position;
@@ -72,7 +72,7 @@ void RenderObject::OnParentChanged(RenderObject* old_parent,
   CRU_UNUSED(new_parent)
 }
 
-void RenderObject::OnAddChild(RenderObject* new_child, int position) {
+void RenderObject::OnAddChild(RenderObject* new_child, Index position) {
   CRU_UNUSED(new_child)
   CRU_UNUSED(position)
 
@@ -80,7 +80,7 @@ void RenderObject::OnAddChild(RenderObject* new_child, int position) {
   InvalidatePaint();
 }
 
-void RenderObject::OnRemoveChild(RenderObject* removed_child, int position) {
+void RenderObject::OnRemoveChild(RenderObject* removed_child, Index position) {
   CRU_UNUSED(removed_child)
   CRU_UNUSED(position)