Why can't RHR functions be overloaded?

Question

I could see something like the following being useful:

class A {
public:
   const vector<int>& vals() const {
       return val;
   }

   vector<int> vals() && {
       return std::move(val);
   }
private:
    vector<int> val;
}

But I get a compiler error with g++:

error: ‘vector<int> A::vals() &&’ cannot be overloaded

I would think you'd be able to do the same sort of overloading that you can with const functions. This would be less useful for the above accessor, and more useful for operators.

Answer 1

The reason is C++11 13.1/2:

...

• Member function declarations with the same name and the same parameter-type-list- as well as member function template declarations with the same name, the same parameter-type-list, and the same template parameter lists cannot be overloaded if any of them, but not all, have a ref-qualifier (8.3.5).

  [ Example:

  class Y {
    void h() &;
    void h() const &; // OK
    void h() &&;      // OK, all declarations have a ref-qualifier
  
    void i() &;
    void i() const;   // ill-formed, prior declaration of i
                      // has a ref-qualifier
  };
  

  —end example ]

In ohter words, your example would work if you added a ref-qualifier to the const overload of vals().