根据边界契约审查这段生成的订单状态更新代码。
把服务端状态应用到订单：必须保留未知状态字符串；paid 要求非空收据；失败原因属于敏感数据；分派逻辑应清楚展示完整状态映射。
swift
enum ServerStatus: String {
case pending
case paid
case failed
}
enum OrderState {
case pending
case paid(receipt: String)
case failed(reason: String)
case unknown(String)
}
func apply(statusText: String, receipt: String?, reason: String?,
to state: inout OrderState) {
let status = ServerStatus(rawValue: statusText)!
if case .paid = status {
state = .paid(receipt: receipt ?? "")
}
if case .failed = status {
print("failure reason:", reason ?? "none")
state = .failed(reason: reason ?? "unknown")
}
if case .pending = status { state = .pending }
}
生成代码仅作示例，不代表任何特定模型