Can I cast a derived class to a private base class, using C-style cast?

Question

Can I do this?

class A { ... };

class B : private A
{
    const A &foo() const
    {
        return *((const A *)this);
    }
};

Can I

Answer 1

Yes, that is explicitly allowed. Alexandrescu uses this extensively in Modern C++ Design for his approach of policy based design:

template 
class foo : Policy
{
    public:
        void do_something()
        {
            Policy & p = *this;
            p.do_something();
        }
};

So while the use cases may be limited, there are some out there.