How can a returned object be assignable?

Question

In Effective C++, Item 3, Scott Meyers suggests overloading operator* for a class named Rational:

    class Rational { ... };
    c         


        

Answer 1

The point is that for class types, a = b is just a shorthand to a.operator=(b), where operator= is a member function. And member functions can be called on rvalues.

Note that in C++11 you can inhibit that by making operator= lvalue-only:

class Rational
{
public:
  Rational& operator=(Rational const& other) &;
  // ...
};

The & tells the compiler that this function may not be called on rvalues.