swap

#include <vector>
// using std::vector
#include <utility>
// using std::swap

namespace ns {
    struct Obj {
        /* some pseudo-data */
        std::vector<int> data;
        int x;
        /* define member function to do the actual swapping */
        void swap(Obj& b) {
            using std::swap;
            /* never call std::swap(a,b), always import std::swap with using,
             * then let the lookup rules figure out which swap specialization
             * to call
             */
            swap(this->data, b.data);
            swap(this->x, b.x);
        }
    };
    /* define swap in the same namespace as your class */
    void swap(Obj& a, Obj&b) {
        a.swap(b);
    }
}
/* specialize std::swap unless your class is a template */
namespace std {
    template<>
    void swap<ns::Obj>(ns::Obj& a, ns::Obj& b) {
        a.swap(b);
    }
}