Practical example of Rvalue references and move semantics

class A
{
public:
    A(int x)
      : x(x)
    {
        std::cout << "A(int x)\n";
    }

    A(const A& a)
       : x(a.x)
    {
        std::cout << "A(const A&)\n";
    }

    A& operator=(const A& a)
    {
        x = a.x;
        return *this;
    }

    A operator+(const A& a)
    {
        return A(x + a.x);
    }

private:
    int x;
};

class B
{
public:
    B(int x)
       : x(x)
    {
        std::cout <<  "B(int x)\n";
    }

    B(const B&amp; b)
       : x(b.x)
    {
        std::cout <<  "B(const B&)\n";
    }

    B(B&& b) 
       : x(std::move(b.x))
    {
        std::cout <<  "B(B&&)\n";
    }

    B&; operator=(const B& b)
    {
        x = b.x;
        return *this;
    }

    B& operator=(B&& b)
    {
        x = std::move(b.x);
        return *this;
    }

    B operator+(const B& b)
    {
        return B(x + b.x);
    }

    B&& operator+(B&& b)
    {
        b.x += x;
        return std::move(b);
    }

private:
    int x;
};

int main(int argc, char* argv[])
{
    A a1(5);
    A a2 = a1 + 2 + 3;

    B b1(5);
    B b2 = b1 + 2 + 3;
    return 0;
}