pub type PJRT_RecvCallback = Option<unsafe extern "C" fn(stream: *mut PJRT_CopyToDeviceStream, user_arg: *mut c_void)>;
pub enum PJRT_RecvCallback { None, Some(unsafe extern "C" fn(*mut PJRT_CopyToDeviceStream, *mut c_void)), }
No value.
Some value of type T.
T