#include <iostream>

class ia
{
public:
    virtual void a1() =0;
    virtual ~ia() {}
};

class ib
{
public:
    virtual void b1() =0;
    virtual ~ib() {}
};

class agg1:    public ia,    public ib
{
public:
    virtual void a1() { std::cout << "a1 in agg1" << std::endl; }
    virtual void b1() { std::cout << "b1 in agg1" << std::endl; }
};


int main()
{
    ia* pa1(new agg1);

    pa1->a1();
    //pa1->b1(); //error

    ib* pb1(dynamic_cast<ib*>(pa1)); // CROSS CAST from ia to ib thanks to agg1

    if(pb1)
    {
      //pb1->a1(); //error
      pb1->b1();	
    }

    delete pa1;

}