老师，想请教一下这个warning是因为什么导致的
event_dispatcher.h:13:26: warning: declaration of ‘struct event_loop’ will not be visible outside of this function [-Wvisibility]
void *(*init)(struct event_loop *);

event_dispatcher.h代码如下：
struct event_dispatcher {
const char *name;

void *(*init)(struct event_loop *);

// add channel event and notify dispatcher
int (*add)(struct event_loop *, struct channel *ch);

// delete channel event and notify dispatcher
int (*del)(struct event_loop *, struct channel *ch);

// update channel event and notify dispatcher
int (*update)(struct event_loop *, struct channel *ch);

// dispatcher and use event_loop callback use event_activate
int (*dispatch)(struct event_loop *, struct timeval *);

void (*clear)(struct event_loop *);

};