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Singletons

Started by InsaneX May 15, 2004 at 3:38 PM 2 replies 400+ views

Original Post

May 15, 2004 at 3:38 PM

I read the article on Singletons on gamedev (The One: A Singleton Discussion). I understand the necessity for them, but I was having trouble understanding the implementations. Meyer''s Singleton seems simple enough to me, but the nifty counter confused me. I was thinking that this could be enough (I like the idea of a template instead of implementing it as part of the class)

template <typename T> class Singleton
{
     static T* SingletonClass;
     public:

     Singleton(){SingletonClass = new T;}

     ~Singleton(){delete SingletonClass;}

     GetInstance(){return *SingletonClass}

     GetPtrInstance(){return *SingletonClass}
};

This is very similar to the Ogre engine implementation, except by some act of god (confusing code that baffles me) they never allocate the pointer with new, and they never delete it.

wild_pointer

152

wild_pointer

May 15, 2004 at 3:51 PM

The whole point of singletons is to enforce only one instance of any given object, not give you a glorified global variable. How does your code do this?

The easiest to understand implementation would probably be


template <class T>
class Singleton 
{
public:
    static T* Instance()
    {
       static T inst;
       return &inst
    }
protected:
    Singleton();
    Singleton(const T&);
    T& operator= (const T&);
};

Note, not threadsafe.

InsaneX

Author

InsaneX

May 15, 2004 at 4:09 PM

I wouldn't worry about it being thread unsafe, I don't plan on using threads. Also, for the singleton in your post, can you just put

Singleton<MyClass>;

without declaring an instance. Unless you implement this into each and every class definition, you can still declare instances of the class. Correct me if any of this is wrong.

[edited by - InsaneX on May 15, 2004 5:10:46 PM]

wild_pointer

152

wild_pointer

May 15, 2004 at 4:27 PM

No, it''s usage would be


class MyClass : public Singleton<MyClass>
{
};

MyClass *Instance = MyClass::Instance();

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