ref BillStatus? State 这个是什么意思？

Question

在BillStatus中是没有State 的啊？

  using (FlowDbContext db = CreateContext(trans))
            {
                BillStatus? state = null;
                db.Submit(
                    billTypeId,
                    billId,
                    flowId,                    ref state
                );                return state.Value;
            }

    public enum BillStatus
    {        /// <summary>
        /// 已提交未审核        /// </summary>
        Submited = 1,        /// <summary>
        /// 已经审核，但未完成        /// </summary>
        Processing = 2,        /// <summary>
        /// 通过流程的        /// </summary>
        Passed = 3,        /// <summary>
        /// 被否决的        /// </summary>
        Rejected = 4
    }

Answer 1

ref进去了被改了啊