Go language: iota identifier

‘iota’ identifier is used in const declarations to simplify definitions of incrementing numbers.

Example

const (

         first = iota

         second

         third

         fourth

)

‘iota’ starts with number 0 and assign subsequent constants by incrementing the variable value by 1.

HelloWorld.go

package main

import "fmt"

const (
 first = iota
 second
 third
 fourth
)

func main() {

 fmt.Println("first : ", first)
 fmt.Println("second : ", second)
 fmt.Println("third : ", third)
 fmt.Println("fourth : ", fourth)

}

Output

first :  0

second :  1

third :  2

fourth :  3

Each ‘const’ block has its own iota.

const (

         block1First = iota

         block1Second

)

const (

         block2First = iota

         block2Second

         block2Third

)

HelloWorld.go

package main

import "fmt"

const (
 block1First = iota
 block1Second
)

const (
 block2First = iota
 block2Second
 block2Third
)

func main() {

 fmt.Println("block1First : ", block1First)
 fmt.Println("block1Second : ", block1Second)
 fmt.Println("block2First : ", block2First)
 fmt.Println("block2Second : ", block2Second)
 fmt.Println("block2Third : ", block2Third)

}

Output

block1First :  0

block1Second :  1

block2First :  0

block2Second :  1

block2Third :  2

Using iota in constant expressions

We can use iota in constant expressions.

const (

         first = 1 << iota

         second

         third

         fourth

         five

         six

)

Value of

first is 1 << 0

second is 1 << 1

third is 1 << 2

fourth is 1 << 3 etc,

HelloWorld.go

package main

import "fmt"

var a int = 10

const (
 first = 1 << iota
 second
 third
 fourth
 five
 six
)

func main() {

 fmt.Println("first : ", first)
 fmt.Println("second : ", second)
 fmt.Println("third : ", third)
 fmt.Println("fourth : ", fourth)
 fmt.Println("five : ", five)
 fmt.Println("six : ", six)

}

Output

first :  1

second :  2

third :  4

fourth :  8

five :  16

six :  32

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