Function swap

3rdparty/cppzmq/zmq.hpp:731–735

    }

    void swap(message_t &other) ZMQ_NOTHROW
    {
        // this assumes zmq::msg_t from libzmq is trivially relocatable
        std::swap(msg, other.msg);
    }

    ZMQ_NODISCARD zmq_msg_t *handle() ZMQ_NOTHROW { return &msg; }
    ZMQ_NODISCARD const zmq_msg_t *handle() const ZMQ_NOTHROW { return &msg; }