c++ - 虚拟成员类的调用方法

Question

我知道 virtual 在成员函数的上下文中是如何工作的，但是我在网上看到一篇关于虚拟成员类的文章让我感到困惑。

我找到的例子是这样的:

class Machine
{
    void run () {}

    virtual class Parts
    {
    };
};

// The inner class "Parts" of the class "Machine" may return the number of wheels the machine has.
class Car: public Machine
{
    void run() { 
        cout << "The car is running." << endl; 
    }
    class Parts
    {
        int get_Wheels () {
            cout << "A car has 4 wheels." << endl;
            return 4;
        }
        string get_Fuel_Type () {
            cout << "A car uses gasoline for fuel." << endl;
            return "gasoline";
        }
    };
};

文章 https://en.wikipedia.org/wiki/Virtual_class声明:

Any object of class type Machine can be accessed the same way. The programmer can ask for the number of wheels (by calling get_Wheels()), without needing to know what kind of machine it is, how many wheels that machine has, or all the possible types of machines there are. Functions like get_Fuel_Type() can be added to the virtual class Parts by the derived class Car.

如何从 Machine* 调用 get_Wheels() 或成员类 Parts 中的任何其他函数？在调用 get_wheels() 之前，您似乎必须知道您拥有哪种类型的 Machine，因为您无法保证该函数具有实现。

Answer 1

您发布的代码不是 C++，因为这种语言不支持您描述的概念中的虚拟类。