go语言学习十一 - 枚举

        go 语言没有定义枚举类型，实现枚举的方式是通过定义一系列的自定义类型的常量来实现，go 语言中关于枚举的极简方式是 go 哲学的典型：go 语言为程序员提供他们所需要的一切，包括很多强大而方便的特性，同时又让语言尽可能的保持简小、连贯而且快速的编译和运行。

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package weeks   type week int //设置为不导出，避免调用者设置超出枚举范围的值 比如 week(8)   const (     Sunday week = iota // if set 0 , the Following const are all 0     Monday     Tuesday     Wednesday     Thursday     Friday     Saturday )   var wnMap = map[week]string{     Sunday:    "Sunday",     Monday:    "Monday",     Tuesday:   "Tuesday",     Wednesday: "Wednesday",     Thursday:  "Thursday",     Friday:    "Friday",     Saturday:  "Saturday", //must end with , }   func (w week) IsRestDay() bool {     return w == Saturday || w == Sunday }   func (w week) String() string {     if v, ok := wnMap[w]; ok {         return v     }     //由于 week 类型设置为私有不导出，其实这个错误不会发生     return "invalid value" }

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package bitflags   import (     "fmt"     "strings" )   type BitFlag int   //const values as other languge enumeration   const (     Active BitFlag = 1 << iota     Send     Receive )   //how to print BitFlag const value func (flag BitFlag) String() string {       var flags []string       //flags := []string{} //warning: Empty slice declaration via literal     //suggestion: (1) var flags []string   (2) flags := make([]string,0)       if flag&Active == Active {         flags = append(flags, "Active")     }       if flag&Send == Send {         flags = append(flags, "Send")     }       if flag&Receive == Receive {         flags = append(flags, "Receive")     }       if len(flags) > 0 {         return fmt.Sprintf("%d(%s)", int(flag), strings.Join(flags, "|")) //这里如果不强制转换为int型将触发String()方法的递归调用死循环     }       return "0()"   }

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package main   import (     "bitflags"     "fmt"     "weeks" )   func main() {     const limit = 512 //类型兼容任何数字类型     const top uint16 = 1421 // const initial can not use  :=     const start = byte(19)  // 指定与默认推断类型不一致的类型 ， 默认推断19为int64       d := weeks.Monday     fmt.Printf("%v is a rest day? %t.\n", d, d.IsRestDay())     fmt.Println(bitflags.Active, bitflags.Send, bitflags.Active|bitflags.Send, bitflags.Active|bitflags.Send|bitflags.Receive) }