Python

def singleton(cls):
    instance = cls()
    instance.__call__ = lambda: instance
    return instance

@singleton
class Highlander:
    x = 100

Java

public class Singleton {  
    private static class SingletonHolder {  
        private static final Singleton INSTANCE = new Singleton();  
    }  
    private Singleton (){}  
    public static final Singleton getInstance() {  
        return SingletonHolder.INSTANCE; 
    }  
}

C++

class Singleton {
public:
    static Singleton& Instance() {
        static Singleton theSingleton;
        return theSingleton;
    }

private:
    Singleton();                            // ctor hidden
    Singleton(Singleton const&);            // copy ctor hidden
    Singleton& operator=(Singleton const&); // assign op. hidden
    ~Singleton();                           // dtor hidden
};