3. Простой вопрос о переброске

#include <iostream>

struct left
{
    void foo() const
    {
        std::cout << "left::foo()" << std::endl;
    }
};

struct right
{
    void foo() const
    {
        std::cout << "right::foo()" << std::endl;
    }
};

struct middle: public left, public right
{

};

int main()
{
    try
    {
        throw middle();
    }
    catch(left const& lft)
    {
        lft.foo();
        try
        {
            throw;
        }
        catch(right const& rgt)
        {
            rgt.foo();
        }
    }

    return 0;
}