Function swap

dlib/member_function_pointer/member_function_pointer_kernel_1.h:171–187

        bool operator!() const { return !is_set(); }

        void swap (
            mfp_kernel_1_base_class& item
        ) 
        {  
            // make a temp copy of item
            mfp_kernel_1_base_class temp(item);

            // destory the stuff in item
            item.destroy_mp_memory();
            // copy *this into item
            mp()->clone(item.mp_memory.get());

            // destory the stuff in this 
            destroy_mp_memory();
            // copy temp into *this
            temp.mp()->clone(mp_memory.get());
        }

    protected: