28     using Callback = fu2::unique_function<void(IO&, int fd, uint32_t revents)>;  typedef in sdeventplus::source::IO
32      *         callback for each IO epoll event observed.
38      *  @param[in] callback - The function executed on event dispatch
40     IO(const Event& event, int fd, uint32_t events, Callback&& callback);
53     /** @brief Sets the callback
55      *  @param[in] callback - The function executed on event dispatch
57     void set_callback(Callback&& callback);
74      *         events trigger the callback action
82      *         trigger the callback handler
90      *         seen in the most recent callback
104     /** @brief Returns a reference to the callback executed for this source
106      *  @return A reference to the callback
108     Callback& get_callback();
122     /** @brief A wrapper around the callback that can be called from sd-event
138     IO::Callback callback;  member in sdeventplus::source::detail::IOData
141     IOData(const IO& base, IO::Callback&& callback);