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 using namespace std; template 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 Derived: public Base { public: Derived(){} Derived(T B, T D): Base(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 *bPtr = new Derived(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 using namespace std; template 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 Derived: public Base { public: Derived(){} Derived(T B, T D): Base(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 Factory { public: // Return a base instance static Base* getInstance(T B) { Base *bPtr = new Base(B); return bPtr; } // Return a derived instance static Base* getInstance(T B, T D) { Base *bPtr = new Derived(B, D); return bPtr; } };

The calling environment in client side:

int main(int argc, char* argv[]) { Base *bPtr = Factory::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。

template<> class Base { public: Base(){} Base(int B):m_B(B){} virtual ~Base(){} virtual void speak() { cout << "I am Base class" << endl; } private: int m_B; };

template<> class Derived: public Base { public: Derived(){} Derived(int B, int D): Base(B), m_D(D){} ~Derived(){} // Static method virtual void speak() { cout << "I am Derived class" << endl; } private: int m_D; };