4 files changed, 22 insertions, 23 deletions
diff --git a/src/platform/native/ui_application.cpp b/src/platform/native/ui_application.cpp
index b4794182..212d9104 100644
--- a/src/platform/native/ui_application.cpp
+++ b/src/platform/native/ui_application.cpp
@@ -2,4 +2,14 @@
 
 namespace cru::platform::native {
 IUiApplication* IUiApplication::instance = nullptr;
+
+IUiApplication::IUiApplication() {
+  if (instance) {
+    throw std::runtime_error("An ui application has already been created.");
+  }
+  
+  instance = this;
 }
+
+IUiApplication::~IUiApplication() { instance = nullptr; }
+}  // namespace cru::platform::native
diff --git a/src/win/native/timer.cpp b/src/win/native/timer.cpp
index ed2ae069..66743963 100644
--- a/src/win/native/timer.cpp
+++ b/src/win/native/timer.cpp
@@ -4,10 +4,10 @@ namespace cru::platform::native::win {
 TimerManager::TimerManager(GodWindow* god_window) { god_window_ = god_window; }
 
 UINT_PTR TimerManager::CreateTimer(const UINT milliseconds, const bool loop,
-                                   const TimerAction& action) {
+                                   TimerAction action) {
   const auto id = current_count_++;
   ::SetTimer(god_window_->GetHandle(), id, milliseconds, nullptr);
-  map_.emplace(id, std::make_pair(loop, action));
+  map_.emplace(id, std::make_pair(loop, std::move(action)));
   return id;
 }
 
diff --git a/src/win/native/timer.hpp b/src/win/native/timer.hpp
index 10658cf1..6c4871dd 100644
--- a/src/win/native/timer.hpp
+++ b/src/win/native/timer.hpp
@@ -21,7 +21,7 @@ class TimerManager : public Object {
 
   ~TimerManager() override = default;
 
-  UINT_PTR CreateTimer(UINT milliseconds, bool loop, const TimerAction& action);
+  UINT_PTR CreateTimer(UINT milliseconds, bool loop, TimerAction action);
   void KillTimer(UINT_PTR id);
   std::optional<std::pair<bool, TimerAction>> GetAction(UINT_PTR id);
 
diff --git a/src/win/native/ui_application.cpp b/src/win/native/ui_application.cpp
index 9ab61551..892acd50 100644
--- a/src/win/native/ui_application.cpp
+++ b/src/win/native/ui_application.cpp
@@ -18,13 +18,7 @@ namespace cru::platform::native::win {
 WinUiApplication* WinUiApplication::instance = nullptr;
 
 WinUiApplication::WinUiApplication() {
-  if (instance) {
-    throw new std::runtime_error(
-        "Already created an instance of WinUiApplication");
-  }
-
   instance = this;
-  IUiApplication::instance = this;
 
   instance_handle_ = ::GetModuleHandleW(nullptr);
   if (!instance_handle_)
@@ -42,10 +36,7 @@ WinUiApplication::WinUiApplication() {
   cursor_manager_ = std::make_unique<WinCursorManager>();
 }
 
-WinUiApplication::~WinUiApplication() {
-  IUiApplication::instance = nullptr;
-  instance = nullptr;
-}
+WinUiApplication::~WinUiApplication() { instance = nullptr; }
 
 int WinUiApplication::Run() {
   MSG msg;
@@ -63,13 +54,13 @@ void WinUiApplication::RequestQuit(const int quit_code) {
   ::PostQuitMessage(quit_code);
 }
 
-void WinUiApplication::AddOnQuitHandler(const std::function<void()>& handler) {
-  quit_handlers_.push_back(handler);
+void WinUiApplication::AddOnQuitHandler(std::function<void()> handler) {
+  quit_handlers_.push_back(std::move(handler));
 }
 
-void WinUiApplication::InvokeLater(const std::function<void()>& action) {
+void WinUiApplication::InvokeLater(std::function<void()> action) {
   // copy the action to a safe place
-  auto p_action_copy = new std::function<void()>(action);
+  auto p_action_copy = new std::function<void()>(std::move(action));
 
   if (::PostMessageW(GetGodWindow()->GetHandle(), invoke_later_message_id,
                      reinterpret_cast<WPARAM>(p_action_copy), 0) == 0)
@@ -77,17 +68,15 @@ void WinUiApplication::InvokeLater(const std::function<void()>& action) {
 }
 
 unsigned long WinUiApplication::SetTimeout(
-    std::chrono::milliseconds milliseconds,
-    const std::function<void()>& action) {
+    std::chrono::milliseconds milliseconds, std::function<void()> action) {
   return static_cast<unsigned long>(timer_manager_->CreateTimer(
-      static_cast<UINT>(milliseconds.count()), false, action));
+      static_cast<UINT>(milliseconds.count()), false, std::move(action)));
 }
 
 unsigned long WinUiApplication::SetInterval(
-    std::chrono::milliseconds milliseconds,
-    const std::function<void()>& action) {
+    std::chrono::milliseconds milliseconds, std::function<void()> action) {
   return static_cast<unsigned long>(timer_manager_->CreateTimer(
-      static_cast<UINT>(milliseconds.count()), true, action));
+      static_cast<UINT>(milliseconds.count()), true, std::move(action)));
 }
 
 void WinUiApplication::CancelTimer(unsigned long id) {