Get rid of GSL.

15 files changed, 79 insertions, 96 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index 45688deb..2414831b 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -73,4 +73,4 @@ else()
 	target_compile_definitions(CruBase PUBLIC CRU_PLATFORM_LINUX)
 endif()
 
-target_link_libraries(CruBase PUBLIC GSL double-conversion)
+target_link_libraries(CruBase PUBLIC double-conversion)
diff --git a/src/common/String.cpp b/src/common/String.cpp
index cac807b0..0d1c38b8 100644
--- a/src/common/String.cpp
+++ b/src/common/String.cpp
@@ -6,7 +6,6 @@
 
 #include <double-conversion/double-conversion.h>
 #include <double-conversion/string-to-double.h>
-#include <gsl/gsl>
 
 #include <algorithm>
 #include <cmath>
diff --git a/src/platform/Color.cpp b/src/platform/Color.cpp
index a35ef535..bbb78628 100644
--- a/src/platform/Color.cpp
+++ b/src/platform/Color.cpp
@@ -1,7 +1,5 @@
 #include "cru/platform/Color.h"
 
-#include <gsl/gsl>
-
 #include <cmath>
 #include <cstdint>
 #include <optional>
@@ -61,9 +59,8 @@ std::optional<Color> Color::Parse(StringView string,
     if (!g) return std::nullopt;
     auto b = get_num_for_two_digit(string.substr(5, 2));
     if (!b) return std::nullopt;
-    return Color(gsl::narrow_cast<std::uint8_t>(*r),
-                 gsl::narrow_cast<std::uint8_t>(*g),
-                 gsl::narrow_cast<std::uint8_t>(*b));
+    return Color(static_cast<std::uint8_t>(*r), static_cast<std::uint8_t>(*g),
+                 static_cast<std::uint8_t>(*b));
   } else if (string_size == 9) {
     if (string[0] != u'#') return std::nullopt;
     auto r = get_num_for_two_digit(string.substr(1, 2));
@@ -74,9 +71,8 @@ std::optional<Color> Color::Parse(StringView string,
     if (!b) return std::nullopt;
     auto a = get_num_for_two_digit(string.substr(7, 2));
     if (!a) return std::nullopt;
-    return Color(
-        gsl::narrow_cast<std::uint8_t>(*r), gsl::narrow_cast<std::uint8_t>(*g),
-        gsl::narrow_cast<std::uint8_t>(*b), gsl::narrow_cast<std::uint8_t>(*a));
+    return Color(static_cast<std::uint8_t>(*r), static_cast<std::uint8_t>(*g),
+                 static_cast<std::uint8_t>(*b), static_cast<std::uint8_t>(*a));
   } else {
     return std::nullopt;
   }
diff --git a/src/platform/graphics/direct2d/WindowRenderTarget.cpp b/src/platform/graphics/direct2d/WindowRenderTarget.cpp
index 0227f084..a8d988f4 100644
--- a/src/platform/graphics/direct2d/WindowRenderTarget.cpp
+++ b/src/platform/graphics/direct2d/WindowRenderTarget.cpp
@@ -4,8 +4,8 @@
 #include "cru/platform/graphics/direct2d/Factory.h"
 
 namespace cru::platform::graphics::direct2d {
-D2DWindowRenderTarget::D2DWindowRenderTarget(
-    gsl::not_null<DirectGraphicsFactory*> factory, HWND hwnd)
+D2DWindowRenderTarget::D2DWindowRenderTarget(DirectGraphicsFactory* factory,
+                                             HWND hwnd)
     : factory_(factory), hwnd_(hwnd) {
   const auto d3d11_device = factory->GetD3D11Device();
   const auto dxgi_factory = factory->GetDxgiFactory();
diff --git a/src/platform/gui/osx/Window.mm b/src/platform/gui/osx/Window.mm
index 8773678d..d6bee564 100644
--- a/src/platform/gui/osx/Window.mm
+++ b/src/platform/gui/osx/Window.mm
@@ -471,7 +471,7 @@ cru::platform::gui::KeyModifier GetKeyModifier(NSEvent* event) {
 - (void)drawRect:(NSRect)dirtyRect {
   auto cg_context = [[NSGraphicsContext currentContext] CGContext];
   auto layer = _p->GetDrawLayer();
-  Ensures(layer);
+  cru::Ensures(layer);
   CGContextDrawLayerAtPoint(cg_context, CGPointMake(0, 0), layer);
 }
 
diff --git a/src/platform/gui/win/InputMethod.cpp b/src/platform/gui/win/InputMethod.cpp
index d9c179ad..4c5b3b8c 100644
--- a/src/platform/gui/win/InputMethod.cpp
+++ b/src/platform/gui/win/InputMethod.cpp
@@ -144,8 +144,7 @@ CompositionText GetCompositionInfo(HIMC imm_context) {
 
 }  // namespace
 
-WinInputMethodContext::WinInputMethodContext(
-    gsl::not_null<WinNativeWindow*> window)
+WinInputMethodContext::WinInputMethodContext(WinNativeWindow* window)
     : native_window_(window) {
   event_guard_ += window->NativeMessageEvent()->AddHandler(
       std::bind(&WinInputMethodContext::OnWindowNativeMessage, this,
diff --git a/src/platform/gui/win/TimerManager.cpp b/src/platform/gui/win/TimerManager.cpp
index 1bc32b51..c6128b85 100644
--- a/src/platform/gui/win/TimerManager.cpp
+++ b/src/platform/gui/win/TimerManager.cpp
@@ -22,7 +22,7 @@ long long TimerManager::SetTimer(TimerType type, int period,
                        std::move(action)};
   if (type == TimerType::Immediate) {
     if (!::PostMessageW(god_window_->GetHandle(), kSetImmediateWindowMessageId,
-                        gsl::narrow<UINT_PTR>(id), 0)) {
+                        static_cast<UINT_PTR>(id), 0)) {
       throw Win32Error(
           ::GetLastError(),
           u"Failed to post window message to god window for set immediate.");
@@ -46,7 +46,7 @@ void TimerManager::CancelTimer(long long id) {
 }
 
 void TimerManager::CreateNativeTimer(TimerInfo* info) {
-  info->native_timer_id = gsl::narrow<UINT_PTR>(info->id);
+  info->native_timer_id = static_cast<UINT_PTR>(info->id);
   ::SetTimer(god_window_->GetHandle(), info->native_timer_id, info->period,
              nullptr);
 }
diff --git a/src/platform/gui/win/UiApplication.cpp b/src/platform/gui/win/UiApplication.cpp
index 90eb20ca..94d6b9c5 100644
--- a/src/platform/gui/win/UiApplication.cpp
+++ b/src/platform/gui/win/UiApplication.cpp
@@ -71,14 +71,14 @@ long long WinUiApplication::SetImmediate(std::function<void()> action) {
 long long WinUiApplication::SetTimeout(std::chrono::milliseconds milliseconds,
                                        std::function<void()> action) {
   return this->timer_manager_->SetTimer(TimerType::Timeout,
-                                        gsl::narrow<int>(milliseconds.count()),
+                                        static_cast<int>(milliseconds.count()),
                                         std::move(action));
 }
 
 long long WinUiApplication::SetInterval(std::chrono::milliseconds milliseconds,
                                         std::function<void()> action) {
   return this->timer_manager_->SetTimer(TimerType::Interval,
-                                        gsl::narrow<int>(milliseconds.count()),
+                                        static_cast<int>(milliseconds.count()),
                                         std::move(action));
 }
 
diff --git a/src/ui/components/Menu.cpp b/src/ui/components/Menu.cpp
index 005147a1..2da38990 100644
--- a/src/ui/components/Menu.cpp
+++ b/src/ui/components/Menu.cpp
@@ -37,14 +37,14 @@ Menu::~Menu() {
   }
 }
 
-void Menu::AddItemAt(Component* item, gsl::index index) {
+void Menu::AddItemAt(Component* item, Index index) {
   Expects(index >= 0 && index <= GetItemCount());
 
   items_.insert(items_.cbegin() + index, item);
   container_.AddChildAt(item->GetRootControl(), index);
 }
 
-Component* Menu::RemoveItemAt(gsl::index index) {
+Component* Menu::RemoveItemAt(Index index) {
   Expects(index >= 0 && index < GetItemCount());
 
   Component* item = items_[index];
@@ -65,7 +65,7 @@ void Menu::ClearItems() {
   container_.ClearChildren();
 }
 
-void Menu::AddTextItemAt(String text, gsl::index index,
+void Menu::AddTextItemAt(String text, Index index,
                          std::function<void()> on_click) {
   MenuItem* item = new MenuItem(std::move(text));
   item->SetOnClick([this, index, on_click = std::move(on_click)] {
diff --git a/src/ui/controls/TextBlock.cpp b/src/ui/controls/TextBlock.cpp
index 79c66865..0dad4f5d 100644
--- a/src/ui/controls/TextBlock.cpp
+++ b/src/ui/controls/TextBlock.cpp
@@ -47,7 +47,7 @@ void TextBlock::SetTextColor(const Color& color) {
       GetUiApplication()->GetGraphicsFactory()->CreateSolidColorBrush(color));
 }
 
-gsl::not_null<render::TextRenderObject*> TextBlock::GetTextRenderObject() {
+render::TextRenderObject* TextBlock::GetTextRenderObject() {
   return text_render_object_.get();
 }
 }  // namespace cru::ui::controls
diff --git a/src/ui/controls/TextBox.cpp b/src/ui/controls/TextBox.cpp
index 66b6bd43..87672b4f 100644
--- a/src/ui/controls/TextBox.cpp
+++ b/src/ui/controls/TextBox.cpp
@@ -53,7 +53,7 @@ bool TextBox::GetMultiLine() const { return service_->IsMultiLine(); }
 
 void TextBox::SetMultiLine(bool value) { service_->SetMultiLine(value); }
 
-gsl::not_null<render::TextRenderObject*> TextBox::GetTextRenderObject() {
+render::TextRenderObject* TextBox::GetTextRenderObject() {
   return text_render_object_.get();
 }
 
diff --git a/src/ui/controls/TextHostControlService.cpp b/src/ui/controls/TextHostControlService.cpp
index d6c40a36..36703986 100644
--- a/src/ui/controls/TextHostControlService.cpp
+++ b/src/ui/controls/TextHostControlService.cpp
@@ -29,7 +29,7 @@ namespace cru::ui::controls {
 TextControlMovePattern TextControlMovePattern::kLeft(
     u"Left", helper::ShortcutKeyBind(platform::gui::KeyCode::Left),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       Utf16PreviousCodePoint(text, current_position, &current_position);
       return current_position;
@@ -37,7 +37,7 @@ TextControlMovePattern TextControlMovePattern::kLeft(
 TextControlMovePattern TextControlMovePattern::kRight(
     u"Right", helper::ShortcutKeyBind(platform::gui::KeyCode::Right),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       Utf16NextCodePoint(text, current_position, &current_position);
       return current_position;
@@ -47,7 +47,7 @@ TextControlMovePattern TextControlMovePattern::kCtrlLeft(
     helper::ShortcutKeyBind(platform::gui::KeyCode::Left,
                             platform::gui::KeyModifiers::ctrl),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       return Utf16PreviousWord(text, current_position);
     });
@@ -56,14 +56,14 @@ TextControlMovePattern TextControlMovePattern::kCtrlRight(
     helper::ShortcutKeyBind(platform::gui::KeyCode::Right,
                             platform::gui::KeyModifiers::ctrl),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       return Utf16NextWord(text, current_position);
     });
 TextControlMovePattern TextControlMovePattern::kUp(
     u"Up", helper::ShortcutKeyBind(platform::gui::KeyCode::Up),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(text)
       auto text_render_object = service->GetTextRenderObject();
       auto rect = text_render_object->TextSinglePoint(current_position, false);
@@ -74,7 +74,7 @@ TextControlMovePattern TextControlMovePattern::kUp(
 TextControlMovePattern TextControlMovePattern::kDown(
     u"Down", helper::ShortcutKeyBind(platform::gui::KeyCode::Down),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(text)
       auto text_render_object = service->GetTextRenderObject();
       auto rect = text_render_object->TextSinglePoint(current_position, false);
@@ -85,7 +85,7 @@ TextControlMovePattern TextControlMovePattern::kDown(
 TextControlMovePattern TextControlMovePattern::kHome(
     u"Home(Line Begin)", helper::ShortcutKeyBind(platform::gui::KeyCode::Home),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       return Utf16BackwardUntil(text, current_position,
                                 [](CodePoint c) { return c == u'\n'; });
@@ -93,7 +93,7 @@ TextControlMovePattern TextControlMovePattern::kHome(
 TextControlMovePattern TextControlMovePattern::kEnd(
     u"End(Line End)", helper::ShortcutKeyBind(platform::gui::KeyCode::End),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       return Utf16ForwardUntil(text, current_position,
                                [](CodePoint c) { return c == u'\n'; });
@@ -103,7 +103,7 @@ TextControlMovePattern TextControlMovePattern::kCtrlHome(
     helper::ShortcutKeyBind(platform::gui::KeyCode::Home,
                             platform::gui::KeyModifiers::ctrl),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       CRU_UNUSED(text)
       CRU_UNUSED(current_position)
@@ -114,7 +114,7 @@ TextControlMovePattern TextControlMovePattern::kCtrlEnd(
     helper::ShortcutKeyBind(platform::gui::KeyCode::End,
                             platform::gui::KeyModifiers::ctrl),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       CRU_UNUSED(text)
       CRU_UNUSED(current_position)
@@ -123,7 +123,7 @@ TextControlMovePattern TextControlMovePattern::kCtrlEnd(
 TextControlMovePattern TextControlMovePattern::kPageUp(
     u"PageUp", helper::ShortcutKeyBind(platform::gui::KeyCode::PageUp),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       CRU_UNUSED(text)
       // TODO: Implement this.
@@ -132,7 +132,7 @@ TextControlMovePattern TextControlMovePattern::kPageUp(
 TextControlMovePattern TextControlMovePattern::kPageDown(
     u"PageDown", helper::ShortcutKeyBind(platform::gui::KeyCode::PageDown),
     [](TextHostControlService* service, StringView text,
-       gsl::index current_position) {
+       Index current_position) {
       CRU_UNUSED(service)
       CRU_UNUSED(text)
       // TODO: Implement this.
@@ -147,9 +147,9 @@ std::vector<TextControlMovePattern> TextControlMovePattern::kDefaultPatterns = {
     TextControlMovePattern::kCtrlHome, TextControlMovePattern::kCtrlEnd,
     TextControlMovePattern::kPageUp,   TextControlMovePattern::kPageDown};
 
-TextHostControlService::TextHostControlService(gsl::not_null<Control*> control)
+TextHostControlService::TextHostControlService(Control* control)
     : control_(control),
-      text_host_control_(dynamic_cast<ITextHostControl*>(control.get())) {
+      text_host_control_(dynamic_cast<ITextHostControl*>(control)) {
   context_menu_ = MakeDeleteLaterPtr<components::PopupMenu>();
 
   SetUpShortcuts();
@@ -224,7 +224,7 @@ void TextHostControlService::SetText(String text, bool stop_composition) {
   text_change_event_.Raise(nullptr);
 }
 
-void TextHostControlService::InsertText(gsl::index position, StringView text,
+void TextHostControlService::InsertText(Index position, StringView text,
                                         bool stop_composition) {
   if (!Utf16IsValidInsertPosition(this->text_, position)) {
     CRU_LOG_ERROR(u"Invalid text insert position.");
@@ -238,21 +238,20 @@ void TextHostControlService::InsertText(gsl::index position, StringView text,
   text_change_event_.Raise(nullptr);
 }
 
-void TextHostControlService::DeleteChar(gsl::index position,
-                                        bool stop_composition) {
+void TextHostControlService::DeleteChar(Index position, bool stop_composition) {
   if (!Utf16IsValidInsertPosition(this->text_, position)) {
     CRU_LOG_ERROR(u"Invalid text delete position.");
     return;
   }
-  if (position == static_cast<gsl::index>(this->text_.size())) return;
+  if (position == static_cast<Index>(this->text_.size())) return;
   Index next;
   Utf16NextCodePoint(this->text_, position, &next);
   this->DeleteText(TextRange::FromTwoSides(position, next), stop_composition);
 }
 
 // Return the position of deleted character.
-gsl::index TextHostControlService::DeleteCharPrevious(gsl::index position,
-                                                      bool stop_composition) {
+Index TextHostControlService::DeleteCharPrevious(Index position,
+                                                 bool stop_composition) {
   if (!Utf16IsValidInsertPosition(this->text_, position)) {
     CRU_LOG_ERROR(u"Invalid text delete position.");
     return 0;
@@ -345,8 +344,7 @@ void TextHostControlService::ScrollToCaret() {
   }
 }
 
-gsl::not_null<render::TextRenderObject*>
-TextHostControlService::GetTextRenderObject() {
+render::TextRenderObject* TextHostControlService::GetTextRenderObject() {
   return this->text_host_control_->GetTextRenderObject();
 }
 
@@ -359,7 +357,7 @@ StringView TextHostControlService::GetSelectedText() {
   return GetTextView().substr(selection.position, selection.count);
 }
 
-void TextHostControlService::SetSelection(gsl::index caret_position) {
+void TextHostControlService::SetSelection(Index caret_position) {
   this->SetSelection(TextRange{caret_position, 0});
 }
 
diff --git a/src/ui/render/ScrollBar.cpp b/src/ui/render/ScrollBar.cpp
index bcef74a2..3e578d37 100644
--- a/src/ui/render/ScrollBar.cpp
+++ b/src/ui/render/ScrollBar.cpp
@@ -84,8 +84,7 @@ std::unique_ptr<platform::graphics::IGeometry> CreateScrollBarArrowGeometry() {
 }
 }  // namespace
 
-ScrollBar::ScrollBar(gsl::not_null<ScrollRenderObject*> render_object,
-                     Direction direction)
+ScrollBar::ScrollBar(ScrollRenderObject* render_object, Direction direction)
     : render_object_(render_object), direction_(direction) {
   arrow_geometry_ = CreateScrollBarArrowGeometry();
 }
@@ -260,12 +259,11 @@ void ScrollBar::InstallHandlers(controls::Control* control) {
   }
 }
 
-gsl::not_null<std::shared_ptr<platform::graphics::IBrush>>
+std::shared_ptr<platform::graphics::IBrush>
 ScrollBar::GetCollapsedThumbBrush() {
-  return collapsed_thumb_brush_
-             ? gsl::not_null(collapsed_thumb_brush_)
-             : gsl::not_null(ThemeManager::GetInstance()->GetResourceBrush(
-                   u"scrollbar.collapse-thumb.color"));
+  return collapsed_thumb_brush_ ? collapsed_thumb_brush_
+                                : ThemeManager::GetInstance()->GetResourceBrush(
+                                      u"scrollbar.collapse-thumb.color");
 }
 
 void ScrollBar::SetCollapsedThumbBrush(
@@ -275,12 +273,12 @@ void ScrollBar::SetCollapsedThumbBrush(
   render_object_->InvalidatePaint();
 }
 
-gsl::not_null<std::shared_ptr<platform::graphics::IBrush>> ScrollBar::GetBrush(
+std::shared_ptr<platform::graphics::IBrush> ScrollBar::GetBrush(
     ScrollBarBrushUsageKind usage, ScrollBarBrushStateKind state) {
   auto b = brushes_[usage][state];
-  return b ? gsl::not_null(b)
-           : gsl::not_null(ThemeManager::GetInstance()->GetResourceBrush(
-                 GenerateScrollBarThemeColorKey(usage, state)));
+  return b ? b
+           : ThemeManager::GetInstance()->GetResourceBrush(
+                 GenerateScrollBarThemeColorKey(usage, state));
 }
 
 // Brush could be nullptr to use the theme brush.
@@ -300,7 +298,7 @@ void ScrollBar::OnDraw(platform::graphics::IPainter* painter,
       auto thumb_state = GetState(ScrollBarAreaKind::Thumb);
       painter->FillRectangle(
           *thumb_rect,
-          GetBrush(ScrollBarBrushUsageKind::Thumb, thumb_state).get().get());
+          GetBrush(ScrollBarBrushUsageKind::Thumb, thumb_state).get());
     }
 
     auto up_slot_rect = GetExpandedAreaRect(ScrollBarAreaKind::UpSlot);
@@ -308,23 +306,23 @@ void ScrollBar::OnDraw(platform::graphics::IPainter* painter,
     if (up_slot_rect)
       painter->FillRectangle(
           *up_slot_rect,
-          GetBrush(ScrollBarBrushUsageKind::Slot, up_slot_state).get().get());
+          GetBrush(ScrollBarBrushUsageKind::Slot, up_slot_state).get());
 
     auto down_slot_rect = GetExpandedAreaRect(ScrollBarAreaKind::DownSlot);
     auto down_slot_state = GetState(ScrollBarAreaKind::DownSlot);
     if (down_slot_rect)
       painter->FillRectangle(
           *down_slot_rect,
-          GetBrush(ScrollBarBrushUsageKind::Slot, down_slot_state).get().get());
+          GetBrush(ScrollBarBrushUsageKind::Slot, down_slot_state).get());
 
     auto up_arrow_rect = GetExpandedAreaRect(ScrollBarAreaKind::UpArrow);
     auto up_arrow_state = GetState(ScrollBarAreaKind::UpArrow);
     if (up_arrow_rect)
       this->DrawUpArrow(
           painter, *up_arrow_rect,
-          GetBrush(ScrollBarBrushUsageKind::Arrow, up_arrow_state).get().get(),
+          GetBrush(ScrollBarBrushUsageKind::Arrow, up_arrow_state).get(),
           GetBrush(ScrollBarBrushUsageKind::ArrowBackground, up_arrow_state)
-              .get()
+
               .get());
 
     auto down_arrow_rect = GetExpandedAreaRect(ScrollBarAreaKind::DownArrow);
@@ -332,17 +330,13 @@ void ScrollBar::OnDraw(platform::graphics::IPainter* painter,
     if (down_arrow_rect)
       this->DrawDownArrow(
           painter, *down_arrow_rect,
-          GetBrush(ScrollBarBrushUsageKind::Arrow, down_arrow_state)
-              .get()
-              .get(),
+          GetBrush(ScrollBarBrushUsageKind::Arrow, down_arrow_state).get(),
           GetBrush(ScrollBarBrushUsageKind::ArrowBackground, down_arrow_state)
-              .get()
               .get());
   } else {
     auto optional_rect = GetCollapsedThumbRect();
     if (optional_rect) {
-      painter->FillRectangle(*optional_rect,
-                             GetCollapsedThumbBrush().get().get());
+      painter->FillRectangle(*optional_rect, GetCollapsedThumbBrush().get());
     }
   }
 }
@@ -416,33 +410,32 @@ ScrollBarBrushStateKind ScrollBar::GetState(ScrollBarAreaKind area) {
   }
 }
 
-HorizontalScrollBar::HorizontalScrollBar(
-    gsl::not_null<ScrollRenderObject*> render_object)
+HorizontalScrollBar::HorizontalScrollBar(ScrollRenderObject* render_object)
     : ScrollBar(render_object, Direction::Horizontal) {}
 
 void HorizontalScrollBar::DrawUpArrow(
     platform::graphics::IPainter* painter, const Rect& area,
-    gsl::not_null<platform::graphics::IBrush*> arrow_brush,
-    gsl::not_null<platform::graphics::IBrush*> background_brush) {
-  painter->FillRectangle(area, background_brush.get());
+    platform::graphics::IBrush* arrow_brush,
+    platform::graphics::IBrush* background_brush) {
+  painter->FillRectangle(area, background_brush);
 
   platform::graphics::util::WithTransform(
       painter, Matrix::Translation(area.GetCenter()),
       [this, arrow_brush](platform::graphics::IPainter* painter) {
-        painter->FillGeometry(arrow_geometry_.get(), arrow_brush.get());
+        painter->FillGeometry(arrow_geometry_.get(), arrow_brush);
       });
 }
 
 void HorizontalScrollBar::DrawDownArrow(
     platform::graphics::IPainter* painter, const Rect& area,
-    gsl::not_null<platform::graphics::IBrush*> arrow_brush,
-    gsl::not_null<platform::graphics::IBrush*> background_brush) {
-  painter->FillRectangle(area, background_brush.get());
+    platform::graphics::IBrush* arrow_brush,
+    platform::graphics::IBrush* background_brush) {
+  painter->FillRectangle(area, background_brush);
 
   platform::graphics::util::WithTransform(
       painter, Matrix::Rotation(180) * Matrix::Translation(area.GetCenter()),
       [this, arrow_brush](platform::graphics::IPainter* painter) {
-        painter->FillGeometry(arrow_geometry_.get(), arrow_brush.get());
+        painter->FillGeometry(arrow_geometry_.get(), arrow_brush);
       });
 }
 
@@ -565,33 +558,32 @@ bool HorizontalScrollBar::CanScrollDown() {
   return render_object_->HorizontalCanScrollDown();
 }
 
-VerticalScrollBar::VerticalScrollBar(
-    gsl::not_null<ScrollRenderObject*> render_object)
+VerticalScrollBar::VerticalScrollBar(ScrollRenderObject* render_object)
     : ScrollBar(render_object, Direction::Vertical) {}
 
 void VerticalScrollBar::DrawUpArrow(
     platform::graphics::IPainter* painter, const Rect& area,
-    gsl::not_null<platform::graphics::IBrush*> arrow_brush,
-    gsl::not_null<platform::graphics::IBrush*> background_brush) {
-  painter->FillRectangle(area, background_brush.get());
+    platform::graphics::IBrush* arrow_brush,
+    platform::graphics::IBrush* background_brush) {
+  painter->FillRectangle(area, background_brush);
 
   platform::graphics::util::WithTransform(
       painter, Matrix::Rotation(90) * Matrix::Translation(area.GetCenter()),
       [this, arrow_brush](platform::graphics::IPainter* painter) {
-        painter->FillGeometry(arrow_geometry_.get(), arrow_brush.get());
+        painter->FillGeometry(arrow_geometry_.get(), arrow_brush);
       });
 }
 
 void VerticalScrollBar::DrawDownArrow(
     platform::graphics::IPainter* painter, const Rect& area,
-    gsl::not_null<platform::graphics::IBrush*> arrow_brush,
-    gsl::not_null<platform::graphics::IBrush*> background_brush) {
-  painter->FillRectangle(area, background_brush.get());
+    platform::graphics::IBrush* arrow_brush,
+    platform::graphics::IBrush* background_brush) {
+  painter->FillRectangle(area, background_brush);
 
   platform::graphics::util::WithTransform(
       painter, Matrix::Rotation(270) * Matrix::Translation(area.GetCenter()),
       [this, arrow_brush](platform::graphics::IPainter* painter) {
-        painter->FillGeometry(arrow_geometry_.get(), arrow_brush.get());
+        painter->FillGeometry(arrow_geometry_.get(), arrow_brush);
       });
 }
 
@@ -712,8 +704,7 @@ bool VerticalScrollBar::CanScrollDown() {
   return render_object_->VerticalCanScrollDown();
 }
 
-ScrollBarDelegate::ScrollBarDelegate(
-    gsl::not_null<ScrollRenderObject*> render_object)
+ScrollBarDelegate::ScrollBarDelegate(ScrollRenderObject* render_object)
     : render_object_(render_object),
       horizontal_bar_(render_object),
       vertical_bar_(render_object) {
diff --git a/src/ui/render/TextRenderObject.cpp b/src/ui/render/TextRenderObject.cpp
index 11548106..135c2d02 100644
--- a/src/ui/render/TextRenderObject.cpp
+++ b/src/ui/render/TextRenderObject.cpp
@@ -77,7 +77,7 @@ std::vector<Rect> TextRenderObject::TextRangeRect(const TextRange& text_range) {
   return text_layout_->TextRangeRect(text_range);
 }
 
-Rect TextRenderObject::TextSinglePoint(gsl::index position, bool trailing) {
+Rect TextRenderObject::TextSinglePoint(Index position, bool trailing) {
   return text_layout_->TextSinglePoint(position, trailing);
 }
 
@@ -107,7 +107,7 @@ void TextRenderObject::SetDrawCaret(bool draw_caret) {
   }
 }
 
-void TextRenderObject::SetCaretPosition(gsl::index position) {
+void TextRenderObject::SetCaretPosition(Index position) {
   if (position != caret_position_) {
     caret_position_ = position;
     if (draw_caret_) {
@@ -136,7 +136,7 @@ void TextRenderObject::SetCaretWidth(const float width) {
 
 Rect TextRenderObject::GetCaretRectInContent() {
   auto caret_pos = this->caret_position_;
-  gsl::index text_size = this->GetText().size();
+  Index text_size = this->GetText().size();
   if (caret_pos < 0) {
     caret_pos = 0;
   } else if (caret_pos > text_size) {
diff --git a/src/ui/style/StyleRuleSet.cpp b/src/ui/style/StyleRuleSet.cpp
index 4deaaefa..7b6454ec 100644
--- a/src/ui/style/StyleRuleSet.cpp
+++ b/src/ui/style/StyleRuleSet.cpp
@@ -37,7 +37,7 @@ void StyleRuleSet::SetParent(std::shared_ptr<StyleRuleSet> parent) {
   RaiseChangeEvent();
 }
 
-void StyleRuleSet::AddStyleRule(StyleRule rule, gsl::index index) {
+void StyleRuleSet::AddStyleRule(StyleRule rule, Index index) {
   Expects(index >= 0 && index <= GetSize());
 
   rules_.insert(rules_.cbegin() + index, std::move(rule));
@@ -45,7 +45,7 @@ void StyleRuleSet::AddStyleRule(StyleRule rule, gsl::index index) {
   RaiseChangeEvent(model::ListChange::ItemAdd(index));
 }
 
-void StyleRuleSet::RemoveStyleRule(gsl::index index, gsl::index count) {
+void StyleRuleSet::RemoveStyleRule(Index index, Index count) {
   Expects(index >= 0);
   Expects(count >= 0 && index + count <= GetSize());