pub type PJ_LOG_FUNCTION = Option<unsafe extern "C" fn(arg1: *mut c_void, arg2: c_int, arg3: *const c_char)>;
enum PJ_LOG_FUNCTION { None, Some(unsafe extern "C" fn(_: *mut c_void, _: i32, _: *const i8)), }
No value.
Some value of type T.
T