stealing_private1.cpp

// Stealing private members, code snippet from:
// https://bloglitb.blogspot.com/2011/12/access-to-private-members-safer.html
//
// See also:
//
// https://stackoverflow.com/q/424104/3093378
// https://stackoverflow.com/questions/12993219/access-private-member-using-template-trick
//
// And also Overload 156 (pg. 22)
// https://members.accu.org/index.php/journals/2776

#include <iostream>

template <typename Tag, typename Tag::type M>
struct Rob {
    friend typename Tag::type get(Tag) { return M; }
};

// use
struct A {
    A(int a) : a(a) {}

  private:
    int a;
};

// tag used to access A::a
struct A_f {
    typedef int A::*type;
    friend type get(A_f);
};

template struct Rob<A_f, &A::a>;

int main() {
    A a(42);
    std::cout << "proof: " << a.*get(A_f()) << std::endl;
}