函数只在调用期间读取Shipment，且不会保存它。哪种参数最准确地表达该契约？

函数只在调用期间读取Shipment，且不会保存它。哪种参数最准确地表达该契约？

1. shipment: &Shipment
2. shipment: Shipment
3. shipment: &mut Shipment
4. shipment: Arc<Mutex<Shipment>>