C++ Primer, Fifth Edition

swap Functions Should Call swap, Not std::swap

There is one important subtlety in this code: Although it doesn’t matter in this particular case, it is essential that swap functions call swap and not std::swap. In the HasPtr function, the data members have built-in types. There is no type-specific version of swap for the built-in types. In this case, these calls will invoke the library std::swap.

However, if a class has a member that has its own type-specific swap function, calling std::swap would be a mistake. For example, assume we had another class named Foo that has a member named h, which has type HasPtr. If we did not write a Foo version ...