How does returning std::make_unique work?

Question

I have a base class and its subclass:

class Base {
    public:
    virtual void hi() {
        cout << \"hi\" << endl;
    } 
};

class Derived : pub         


        

Answer 1

In the above listed example, (1) returns an rvalue but (2) is not an rvalue and is attempting a copy on the unique_ptr, which you cannot do for a unique_ptr.

Using move works because you are treating the unique_ptr at that point as an rvalue.