C++, std::list, assignment, inheritance

Question

class A, B;
class A {
    public:
        A& operator= ( const A &rhs ) { return *this; }
};
class B: public A {
    public:
        B& operator= ( const A &rhs ) { return *this; }
};
A a;
B b;
std::list < A > aa;
std::list < B > bb;
a = b; // works
b = a; // works
// aa = bb; // fails
// bb = aa; // fails

How do I get bb = aa to work?

Answer 1

What you're missing here is that even though A and B are related types, std::list<A> and std::list<B> are actually unrelated types (other than both saying list). As such you can't use copy assignment to assign between them.

However, assuming that you're ok assigning the types A and B to each other using their assignment operators, you can use list's assign method to copy the range of iterators:

aa.assign(bb.begin(), bb.end());
bb.assign(aa.begin(), aa.end());