4 iota enum examples

yourbasic.org/golang

Iota basic example

Start from one
Skip value

Complete enum type with strings

Naming convention

Iota basic example

The iota keyword represents successive integer constants 0, 1, 2,…
It resets to 0 whenever the word const appears in the source code,
and increments after each const specification.

const (
	C0 = iota
	C1 = iota
	C2 = iota
)
fmt.Println(C0, C1, C2) // "0 1 2"

This can be simplified to

const (
	C0 = iota
	C1
	C2
)

Here we rely on the fact that expressions are implicitly repeated in a parenthesized const declaration – this indicates a repetition of the preceding expression and its type.

Start from one

To start a list of constants at 1 instead of 0, you can use iota in an arithmetic expression.

const (
	C1 = iota + 1
	C2
	C3
)
fmt.Println(C1, C2, C3) // "1 2 3"

Skip value

You can use the blank identifier to skip a value in a list of constants.

const (
	C1 = iota + 1
	_
	C3
	C4
)
fmt.Println(C1, C3, C4) // "1 3 4"

Complete enum type with strings [best practice]

Here’s an idiomatic way to implement an enumerated type:

create a new integer type,
list its values using iota,
give the type a String function.

type Direction int

const (
	North Direction = iota
	East
	South
	West
)

func (d Direction) String() string {
	return [...]string{"North", "East", "South", "West"}[d]
}

In use:

var d Direction = North
fmt.Print(d)
switch d {
case North:
	fmt.Println(" goes up.")
case South:
	fmt.Println(" goes down.")
default:
	fmt.Println(" stays put.")
}
// Output: North goes up.