How to ensure the move constructor is used

Question

The code below gives the error:

use of deleted function ‘constexpr B::B(const B&)’

now, I know this happens because the copy constructor is (intentionally) implicitly deleted by specifying a move constructor, and that copying the vector causes the calls to the (deleted) copy constructor. I think I also understand why the vector's copy constructor and assignment operator are used. I clearly want to use the move constructor and assignment operator though: move the object, so also move the vector it contains. So, how do I get my move constructor/assignment operator to use the vector's move constructor/assignment operator?

Here is the code:

#include <vector>

class B {
private:
    /* something I don't want to copy */
public:
    B() {};
    B(B&& orig) {/* move contents */};
    B& operator=(B&& rhs) {
        /* move contents */
        return *this;
    };
};

class A {
private:
    vector<B> vec;
public:
    A() : vec() {};
    A(A&& orig) : vec(orig.vec) {};
    A& operator=(A&& rhs) {
        vec = rhs.vec;
        return *this;
    };
};

Answer 1

Just call std::move on the vectors in the expression in which you want to move from them:

class A {
private:
    vector<B> vec;
public:
    A() : vec() {};
    A(A&& orig) : vec(std::move(orig.vec)) {};
    //                ^^^^^^^^^
    A& operator=(A&& rhs) {
        vec = std::move(rhs.vec);
        //    ^^^^^^^^^
        return *this;
    };
};

Even though you take in rvalue references, rhs and orig are still lvalues in the function, so you need to call std::move on them.