unique_ptr_example.cpp

// Thank you std::unique_ptr!
// Compile with
// clang++ unique_ptr.cpp -o unique_ptr -std=c++11 -stdlib=libc++ && ./unique_ptr

/* OUTPUT:
--- START ---
Game
--- MAIN ---
Screen
MainScreen
--- GAME ---
Screen
PlayScreen
~MainScreen
~Screen
--- QUIT ---
~Game
~PlayScreen
~Screen
*/

#include <iostream>
#include <memory>

struct IScreen{
  IScreen(){
		std::cout << "Screen" << std::endl;
	}
	
	virtual ~IScreen(){
		std::cout << "~Screen" << std::endl;
	}
};

struct MainScreen : public IScreen{
	
	MainScreen(){
		std::cout << "MainScreen" << std::endl;
	}
	
	virtual ~MainScreen(){
		std::cout << "~MainScreen" << std::endl;
	}
};

struct PlayScreen : public IScreen{
	
	PlayScreen(){
		std::cout << "PlayScreen" << std::endl;
	}
	
	virtual ~PlayScreen(){
		std::cout << "~PlayScreen" << std::endl;
	}
};

struct Game{

	Game() : screen() {
		std::cout << "Game" << std::endl;
	}

	~Game(){
		std::cout << "~Game" << std::endl;
	}
	
	void LoadScreen(IScreen *s){
		screen = std::unique_ptr<IScreen>(s);
	}

	void LoadMain(){
		MainScreen *ms = new MainScreen;
		LoadScreen(ms);
	}
	
	void LoadPlay(){
		PlayScreen *ps = new PlayScreen;
		LoadScreen(ps);
	}
	
	
	std::unique_ptr<IScreen> screen;
};

int main(){
	
	std::cout << "--- START ---" << std::endl;
	Game g;
	
	// Main screen
	std::cout << "--- MAIN ---" << std::endl;
	g.LoadMain();
	
	// Play screen
	std::cout << "--- GAME ---" << std::endl;
	g.LoadPlay();

	std::cout << "--- QUIT ---" << std::endl;
	return 0;
}