如何在多重继承中实现具有相同名称的虚函数 [英] How to implement virtual functions with the same name in multiple inheritance

问题描述

有如下代码

// A has a virtual function F().
class A
{
public:
    virtual void F() {};
};

// The same for B.
class B
{
public:
    virtual void F() {};
};

// C inherits A and B.
class C : public A, public B
{
public:
    // How to implement the 2 virtual functions with the same name but from
    // different base classes.
    virtual F() {...}
};

请注意，基类中有一个默认的F（）实现。

Note that there is a default implementation of F() in the base classes.

感谢Jan Herrmann和Spook。下面是一个更简单的解决方案，如果我们必须使用一些额外的帮助？

Thanks to Jan Herrmann and Spook. Is the below a simpler solution if we have to use some extra helpers?

#include <iostream>

// A has a virtual function F().
class A
{
private:
    virtual void A_F() {}

public:
    void F() {return A_F();};
};

// The same for B.
class B
{
private:
    virtual void B_F() {}

public:
    void F() {return B_F();};
};

// C inherits A and B.
class C : public A, public B
{
private:
    virtual void A_F() {std::cout << "for A\n";}
    virtual void B_F() {std::cout << "for B\n";}

};

int main()
{
    C c;
    c.A::F();
    c.B::F();
    return 0;
}

推荐答案

class C_a 
  : public A
{
  virtual void F_A() = 0;
  virtual void F() { this->F_A() };
};

class C_b
  : public B
{
  virtual void F_B() = 0;
  virtual void F() { this->F_B() };
};

class C
  : public C_a
  , public C_b
{
  void F_A() { ... }
  void F_B() { ... }
};

如果我记得正确，ISO委员会想到了这个问题，并讨论了语言的变化。但是...有人发现这个很好的方法来解决这个问题： - ）

If I'm remembing right the ISO committee thought about this problem and discussed a change of the language. But then ... somebody found this nice way to solve this problem :-)

你的第二个解决方案是更好的，如果你能够改变你的类层次结构。您可能在 http://www.gotw.ca/publications/mill18.htm为什么它更好的描述。

Your second solution is better in case your are able to change your class hierarchy. You may have a lock at http://www.gotw.ca/publications/mill18.htm for a description why it is better.

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