c++ - 基于策略的设计中的模糊继承

Question

我有一个主机类，它采用两个策略:sayhello 和talk。策略 talk 是一个类模板，它本身采用例如打个招呼。 问题是 sayhello::saySomething 在 host2 中不明确(我尝试用 virtual 解决这个菱形继承(钻石问题))。

我该如何解决这个歧义？或者对于此类问题是否有更好的设计？

示例:

#include <iostream>

class sayhello {
protected:
    void saySomething(void) {
        std::cout<<"Hello!"<<std::endl;
    }
};

template<typename T>
class talk : private T {
protected:
    void doSomething(void) {
        T::saySomething();
    }
};

template<typename T>
class host1 : virtual T {
public:
    void hostAction(void) {
        T::doSomething();
    }
};

template<typename T, typename L>
class host2 : private T, private L {
public:
    void hostAction(void) {
        T::doSomething();
        L::saySomething();
    }
};

int main() {
    host1<talk<sayhello> > HOST1;
    HOST1.hostAction(); // ok that works

    host2<talk<sayhello>,sayhello> HOST2;
    HOST2.hostAction(); // error, ambiguity!

    return 0;
}

Answer 1

您可能滥用继承，但只需在 talk 和 host2 中添加几个 virtual 关键字即可:

#include <iostream>

class sayhello {
protected:
    void saySomething(void) {
        std::cout<<"Hello!"<<std::endl;
    }
};

template<typename T>
class talk : virtual T {
protected:
    void doSomething(void) {
        T::saySomething();
    }
};

template<typename T>
class host1 : virtual T {
public:
    void hostAction(void) {
        T::doSomething();
    }
};

template<typename T, typename L>
class host2 : virtual T, virtual L {
public:
    void hostAction(void) {
        T::doSomething();
        L::saySomething();
    }
};

int main() {
    host1<talk<sayhello> > HOST1;
    HOST1.hostAction(); // ok that works

    host2<talk<sayhello>,sayhello> HOST2;
    HOST2.hostAction(); // error, ambiguity!

    return 0;
}

Live Example