Hands-On Design Patterns with C++

Using swap correctly

Up until now, we have switched between calling a swap() member function, a swap() non-member function, and the explicitly qualified std::swap() operation, without any pattern or reason. We should now bring some discipline to this matter.

First of all, it is always safe and appropriate to call the swap() member function as long as you know that it exists. The latter qualification usually comes up when writing template code—when dealing with concrete types, you typically know what interface they provide. This leaves us with just one question—when calling the swap() non-member function, should we use the std:: prefix?

Consider what happens if we do, as shown here:

namespace N {class C {    public: void swap(C& rhs) noexcept; ...