Update example to use type erased polymorphism technique

src/window.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <memory>
+#include <optional>
 
 namespace starter_window
 {
@@ -17,11 +18,41 @@ struct WindowCreateParams
 class Window
 {
 public:
-	virtual ~Window() = default;
-	virtual void PumpMessages() = 0;
-	virtual bool ShouldClose() = 0;
+	template<typename T>
+	Window(T t) 
+		: self{std::make_unique<model_t<T>>(std::move(t))}
+	{
+	}
+
+	~Window() = default;
+	Window(Window&&) = default;
+	Window& operator=(Window&&) = default;
+	Window(const Window&) = delete;
+	Window operator=(const Window&) = delete;
+
+	friend void PumpMessages(Window& window) { window.self->PumpMessages_(); }
+	friend bool ShouldClose(const Window& window) { return window.self->ShouldClose_(); }
+
+private:
+	struct concept_t
+	{
+		virtual ~concept_t() = default;
+		virtual void PumpMessages_() = 0;
+		virtual bool ShouldClose_() const = 0;
+	};
+
+	template<typename T>
+	struct model_t final : concept_t
+	{
+		model_t(T&& data) : m_data(std::move(data)) {}
+		virtual void PumpMessages_() override{ PumpMessages(m_data); }
+		virtual bool ShouldClose_() const override { return ShouldClose(m_data); }
+		T m_data;
+	};
+
+	std::unique_ptr<concept_t> self;
 };
 
 }
 
-std::unique_ptr<starter_window::Window> swCreateWindow(starter_window::WindowCreateParams params);
+starter_window::Window swCreateWindow(starter_window::WindowCreateParams params);