由于担心中文翻译产生歧义，附上英文原题目：Rewrite template classes to use inheritance without changing the calling environment which required a static function call, but static functions can't be virtual. 英文原题描叙地址

我感觉题目大概意思是，需要改写或更新一个服务端的class，使得客户端调用相关API的时候，不需要修改接口。这里我只想到了用工厂模式来解决，当然不确定对不对。另外，static function是不能够virtual，所以继承的时候，静态函数重写(overriden)是不允许，有没有方式解决这个问题？

总的来说，我觉得此题考点包含三个：

1. Code maintenance in server side

2. Design pattern, mainly for factory method

3. Any trick to overide static function in class inheritance

当然我不确定对题目的理解有没有错误。其实我不是很确定题目是想问，用继承的方式来重新修改这个class？还是重新修改这个类，这个类被其它子类继承了？

我目前还没有找到最佳答案。所以我先给出当前我能想到的答案。欢迎大家的补充和修正。万分感谢THX！！

The original code in server side:

 #include<iostream>

using namespace std;

template<class T>
class Base
{
    public:
        Base(){}
        Base(T B):m_B(B){}
        virtual ~Base(){}

        // Static method
        static void speak()
        {
            cout << "I am Base class" << endl;
        }

    private:
        T m_B;

};


template<class T>
class Derived: public Base<T>
{
    public:
        Derived(){}
        Derived(T B, T D): Base<T>(B), m_D(D){}
        ~Derived(){}

        // Static method
        static void speak()
        {
            cout << "I am Derived class" << endl;
        }

    private:
        T m_D;

};

The calling environment in client side:

 int main(int argc, char* argv[])
{
    Base<int> *bPtr = new Derived<int>(5, 10);
    bPtr->speak();
    delete bPtr;
    return 0;
}

Output:

I am Base class

(obviously no overrding for static function)

////////////////////////////////////////////////////////////////////////////////

My rewrote code in server side:

 #include<iostream>

using namespace std;

template<class T>
class Base
{
    public:
        Base(){}
        Base(T B):m_B(B){}
        virtual ~Base(){}

        // Static method
        static void speak()
        {
            cout << "I am Base class" << endl;
        }
        // Non-static method
        virtual void call_speak()
        {
            speak();    
        }     
    private:
        T m_B;

};


template<class T>
class Derived: public Base<T>
{
    public:
        Derived(){}
        Derived(T B, T D): Base<T>(B), m_D(D){}
        ~Derived(){}

        // Static method
        static void speak()
        {
            cout << "I am Derived class" << endl;
        }
        // Non-static method
        void call_speak()
        {
            speak();    
        }     
    private:
        T m_D;

};

template<class T>
class Factory
{
    public:
        // Return a base instance
        static Base<T>* getInstance(T B)
        {
            Base<T> *bPtr = new Base<T>(B);
            return bPtr;
        }

        // Return a derived instance
        static Base<T>* getInstance(T B, T D)
        {
            Base<T> *bPtr = new Derived<T>(B, D);
            return bPtr;
        }
};

The calling environment in client side:

 int main(int argc, char* argv[])
{
    Base<int> *bPtr = Factory<int>::getInstance(5, 10);
    bPtr->speak();
    bPtr->call_speak();
    delete bPtr;
    return 0;
}

Output:

I am Base class

I am Derived class

主要修改：

1. 使用了工厂模式，把产生对象的过程隐藏起来。

2. 用虚非静态函数的方式重新封装静态函数。