13.1.5. Using = default

We can explicitly ask the compiler to generate the synthesized versions of the copy-control members by defining them as = default (§ 7.1.4, p. 264):

class Sales_data {
public:
    // copy control; use defaults
    Sales_data() = default;
    Sales_data(const Sales_data&) = default;
    Sales_data& operator=(const Sales_data &);
    ~Sales_data() = default;
    // other members as before
};
Sales_data& Sales_data::operator=(const Sales_data&) = default;

When we specify = default on the declaration of the member inside the class body, the synthesized function is implicitly inline (just as is any other member function defined in the body of the class). If we do not want the synthesized member to be an inline function, we can specify = default on the member’s definition, as we do in the definition of the copy-assignment operator.