程序设计实习期中：多态，求解答

#include <iostream>
using namespace std;

class Base {
public:
   virtual Base& fun() { cout << "base fun" << endl; return *this; }
   virtual Base& foo() { cout << "base foo" << endl; return *this; }
};

class Derived: public Base {
public:
   Base& fun() { cout << "derived fun" << endl; return *this; }
   Base& foo() { cout << "derived foo" << endl; return *this; }
};

Base& foo();
Base& fun();
// 在此处补充你的代码
int main() {
   foo().fun().foo();
   fun().foo().fun();
   return 0;
}

输入：
无
输出：
derived foo
derived fun
derived foo
base fun
base foo
base fun

求解答补充代码，谢谢

// Q758999.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"


#include <iostream>
using namespace std;

class Base {
public:
   virtual Base& fun() { cout << "base fun" << endl; return *this; }
   virtual Base& foo() { cout << "base foo" << endl; return *this; }
};

class Derived: public Base {
public:
   Base& fun() { cout << "derived fun" << endl; return *this; }
   Base& foo() { cout << "derived foo" << endl; return *this; }
};

Base& foo();
Base& fun();

// 在此处补充你的代码
Base& foo()
{
    Derived * d = new Derived();
    d->foo();
    return *d;
}

Base& fun()
{
    Base * b = new Base();
    b->fun();
    return *b;
}

int main() {
   foo().fun().foo();
   fun().foo().fun();
   return 0;
}