Recurring Template Idiom-优快云博客

本文介绍了一种使用模板元编程技术来自动选择派生类中的方法实现，以模拟虚函数的行为。通过这种方式，避免了随着派生类数量增加而导致的代码难以维护的问题。

#include <iostream>
using namespace std;

class Base
{
public:
    void foo();
};

class Derive : public Base
{
public:
    void foo() const
    {
        cout <<"Derive." <<endl;
    }
};

void Base::foo()                // Defination of 'Base::foo' must be 
{
    static_cast<Derive *>(this)->foo();
}

int _tmain(int argc, _TCHAR* argv[])
{
    Derive d;

    Base *p = &d;
    p->foo();                    // Simulate 'virtual function'.

    return 0;
}

　　We can use 'static_cast<Derive *>' to use funtion in derived class, but if we have another derived class? 'class Derive2 : public Base; class Derive3 : public Base...'. In that way, we have to distinct derived class and cast 'this' pointer to corresponding derived class. With the increasement of derived class, our code is going to be unmaintainable, which is terrible!

Solution:

template <typename T>
class Base
{
public:
    void foo()
    {
        static_cast<T *>(this)->foo();     // Solve the problem!
    }
};

class Derive : public Base<Derive>         // Recurring Template Idiom.
{
public:
    void foo()
    {
        cout <<"Derive." <<endl;
    }
};