虚函数返回自己类型指针或引用，重写时返回类型可以不一样

C++

#include <functional>
#include <iostream>
#include <vector>
#include <memory>
#include <set>
#include <map>
#include <string>

using namespace std;

namespace
{
    /*C++ 类不能继承它自己*/
    class Animal /*:public Aniaml*/
    {
    public:
        Animal(string n)
        {
            name = n;
        }
        virtual const Animal* getSelf()
        {
            return this;
        }
    public:
        string name;
    };

    class Dog :public Animal
    {
    public:
        Dog(string n, int a) :Animal(n)
        {
            age = a;
        }
        //const Animal* getSelf() override
        const Dog* getSelf() override
        {
            return this;
        }
    public:
        int age;
    };
}

#if 1

int main()
{
    Dog dog("小狗", 2);

    Animal* animal = &dog;
    const Animal* p_animal = animal->getSelf();
    // 这个只能访问到它自己类型的
    cout << "名字：" << p_animal->name << endl;

    const Dog* p_dog = dog.getSelf();
    cout << "名字：" << p_dog->name << endl;
    cout << "年龄：" << p_dog->age << endl;

    return 0;
}

#endif

虚函数 virtual const Animal* getSelf()在派生类可以返回const Dog* getSelf() override，这样就可以不用进行类型转换了。

C#

经测试，C# 好像不支持这种写法。C#9.0 支持这种协变返回类型？