Question

Is it possible to make a generic singleton? I want to create something I can just inherit from and get the functionality of a singleton. I’m having trouble with using templates with static members.

Shouldn’t this work?

**

UPDATED

**

Thanks for the replies so far. So now my problem is that GameEngine can’t see it’s own constructor. I know it’s private but still.

Singleton.h

template <typename T>
class Singleton
{
private:
    static std::shared_ptr<T> m_Instance;
public: 
    static std::shared_ptr<T> Instance();
};

template<typename T>
std::shared_ptr<T> Singleton<T>::m_Instance = nullptr;

template<typename T>
std::shared_ptr<T> Singleton<T>::Instance()
{
if(m_Instance == nullptr)
    m_Instance = std::make_shared<T>();

return m_Instance;
}

GameEngine.h

class GameEngine : public Singleton<GameEngine>
{
private:
GameEngine();

};

Answer 1

The best way to create a singleton is as follows:

class GameEngine
{
public:
    static GameEngine& instance() { static GameEngine e; return e; }

private:
    GameEngine() {}
    GameEngine(const GameEngine&) = delete;
};

The e variable will be (thread-safely) initialized on first call to instance, and it will be destroyed on orderly process exit. The private/deleted constructors prevent a second instance from ever being created.