Struct Event 

#[non_exhaustive]
pub struct Event<U: UserData> {
    pub user_data: U,
    pub flags: EventFlags,
    pub fd: usize,
}

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

user_data: U

flags: EventFlags

fd: usize