哪个基类调用派生重写方法？

Question

我有以下代码使用多重继承.目的是在派生类中使用两个接口作为一个接口:

struct InterfaceA
{
    virtual void register_stuff();
    virtual void on_state_changed( const State state ) = 0;
};

struct InterfaceB
{
    virtual void register_stuff();
    virtual void on_state_changed( const State state ) = 0;
};

struct Derived : InterfaceA, InterfaceB
{
    void register_stuff() override
    {
        InterfaceA::register_stuff();
        InterfaceB::register_stuff();
    }

    void on_state_changed( const State state ) override
    {
        // how can I know who is responding?
    }
};

注册接口将导致异步调用on_state_changed.是否有可能辨别哪个接口正在调用它？

Answer 1

您必须在中间添加一个图层才能消除歧义.这是一个小型实用程序,可以即时创建它们:

template<class Inteface>
struct disambiguate : Interface {
  void on_state_changed( const State state ) override final {
    on_state_changed(state, this);
  }
  virtual void on_state_changed( const State &state, disambiguate* ) = 0;
};

就是这样.然后,根据此实用程序定义您的类是一个问题:

struct Derived : disambiguate<InterfaceA>, disambiguate<InterfaceB>
{
    void register_stuff() override
    {
        InterfaceA::register_stuff();
        InterfaceB::register_stuff();
    }

    void on_state_changed( const State &state, disambiguate<InterfaceA>* ) override
    {
        // Called for A
    }

    void on_state_changed( const State &state, disambiguate<InterfaceB>* ) override
    {
        // Called for B
    }
};

我已经使用了另一个参数和重载来使这个模板化,但是技术本身也可以通过编写类并使用新名称调用虚函数来完成.关键是使原始虚拟调用(通过接口指针)到达调用消除歧义的函数的短thunk.