基类列表中不能有重复出现的基类

派生类的基类列表中不能有重复出现的基类。下列代码会报错：

#include <iostream>
using namespace std;

class Base1{
};
class Base2{
};
class Drived: public Base1, public Base2, public Base2{
};
void main(){
	Drived drived;
}