枚举

  很多时候，由于字符串的所占据空间较大，而某些状态的值是一定的，所以我们希望用枚举来固定对应的值。这样不仅可以节省空间，更关键的是可以方便后期的维护
  我们这里以主机管理为例，状态有 Running 运行中， OffLine 离线， Except 异常
  我们跳过原文章中方法逐步优化的过程，直接到最完善的版本，即使用数字表示状态和使用类型别名的方法，最后通过手动逻辑方法来实现golang中的枚举

枚举的终极办法，原文3.0版本

package mainimport ("encoding/json""fmt"
)type Status int // 类型别名// 定义running、except、offline对应的常量，本质为整数数据
// 通过定义常量我们可以在查询时直接返回这里的常量名，而不是数字等容产生歧义
const ( //在线、异常、离线Running Status = iota + 1 // iota为golang中常量的行索引，起步为0，每行+1ExceptOffline
)type Host struct {ID     uint   `gorm:"json:id"`Name   string `gorm:"json:name"`Status Status `gorm:"json:status"`
}// 在status的json序列化过程中进行常量和字符串的转化
func (status Status) MarshalJSON() ([]byte, error) {var str string //定义一个字符串方便对status的json转换switch status {case Running:str = "running"case Except:str = "except"case Offline:str = "offline"}return json.Marshal(str)}func main() {//定义一个host主机实例var host = Host{Status: Running,Name:   "wang2",}result, _ := json.Marshal(host) //序列化host为json以存储fmt.Printf(string(result))//查询结果如下，可以看到status的值这里查询为字符//{"ID":0,"Name":"wang2","Status":"running"}
}

枚举的实现举例

package mainimport ("encoding/json""fmt""time"
)type WeekDay int //定义一个数值的类型别名，方便显示var WeekStringList = []string{"Sunday", "Monday", "Tuesday", "Thursday", "Wednesday", "Friday", "Saturday"}
var WeekTypeList = []WeekDay{Sunday, Monday, Tuesday, Thursday, Wednesday, Friday, Saturday}func (WeekDay WeekDay) String() string {s := WeekStringList[WeekDay-1]fmt.Println(s)return s
}func (WeekDay WeekDay) MarshalJSON() ([]byte, error) {s, _ := json.Marshal(WeekDay.String())return s, nil
}// 超级落后
const (Sunday WeekDay = iota + 1MondayTuesdayWednesdayThursdayFridaySaturday
)/*func (WeekDay WeekDay) MarshalJSON() ([]byte, error) {var str stringswitch WeekDay {case Sunday:str = "Sunday"case Monday:str = "Monday"case Tuesday:str = "Tuesday"case Thursday:str = "Thursday"case Wednesday:str = "Wednesday"case Friday:str = "Friday"case Saturday:str = "Saturday"}return json.Marshal(str)}
*/type DayInfo struct {WeekDay WeekDay   `json:"WeekDay"`Data    time.Time `json:"Data"`
}func main() {December7th := DayInfo{WeekDay: Wednesday,Data:    time.Now(),}re, _ := json.Marshal(December7th)fmt.Printf(string(re))
}