pub type pw_work_func_t = Option<unsafe extern "C" fn(obj: *mut c_void, data: *mut c_void, res: c_int, id: u32)>;
pub enum pw_work_func_t { None, Some(unsafe extern "C" fn(*mut c_void, *mut c_void, i32, u32)), }
No value.
Some value of type T.
T