Golang : On enumeration



Tags : enumeration golang const iota

In Golang, it is fairly simple to declare enumeration. Just group the similar items into a const group and use the iota keyword.

For example, to declares constants :

 const Monday = 1
 const Tuesday = 2

Enumeration is formed by putting constants into parentheses. For example :

 const ( 
 Monday = 1
 Tuesday = 2
 Wednesday = 3
 )

Golang has one keyword iota that make the consts into enum.

 const ( 
 Monday = iota
 Tuesday 
 Wednesday
 )

and let say you want to explicit declare the constants type. You can do something like :

 type Day int

 const (
 Monday Day = iota 
 Tuesday 
 Wednesday
 )

and this code will test out the enumeration :

 package main

 import (
 "fmt"
 )

 type Day int

 const (
 Monday Day = iota // starts from 0
 Tuesday
 Wednesday
 Thursday
 Friday
 )

 func main() {
 fmt.Println(Monday) // should return 0

 fmt.Println(Friday) // should print 4
 }

Output :

0

4

add a variable and a method to print out the string value instead of iota.

  // [...] is to tell the Go intrepreter/compiler to figure out the array size
 var days = [...]string {"Monday","Tuesday","Wednesday","Thursday","Friday",}

 func (day Day) String() string {
 return days[day]
 }

and the codes below will printout the enumeration in string.

 package main

 import (
 "fmt"
 )

 type Day int

 const (
 Monday Day = iota // starts from 0
 Tuesday
 Wednesday
 Thursday
 Friday
 )

 // [...] is to tell the Go intrepreter/compiler to figure out the array size

 var days = [...]string {"Monday","Tuesday","Wednesday","Thursday","Friday",}

 func (day Day) String() string {
 return days[day]
 }

 func main() {
 fmt.Println(Monday) // should return Monday

 fmt.Println(Friday) // should print Friday
 }

Output :

Monday

Friday



Tags : enumeration golang const iota

By Adam Ng

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