c++ - 如何同时使用单例和纯虚函数？

Question

class base{
        static base* m_selfInstance;
    public:
        static base* GetInstance();
        virtual void abc() = 0;
    };
    class der:public base{
    public:
        void abc(){cout << "Derived...\n";}
    };
    base* base::m_selfInstance = NULL;
    base* base::GetInstance()
        {
            if(m_selfInstance == NULL)
            {
    /*Throws error here and it's natural, because it's violates C++ standard*/
                    m_selfInstance = new base();    
                }
                return m_selfInstance;
            }
            int main()
            {
                base *b = base::GetInstance();
                //b->abc();
            system("pause");
            return 0;
            }

在这种情况下如何一起处理单例和纯虚函数。如果我能做出类似的m_selfInstance = new der();事情就好了。但真正的问题是如果有more derived classeslikeder_1并且der_2那个时候 istance 将m_selfInstance = new der();不是new der_1()or new der_2()。请指导我如何继续进行。