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Go Enums

An enum is a set of named whole-number values. Each name in the set stands for one number.

Counting with iota

iota starts at 0 in this const block. The three names print in order as 0, 1, and 2.

package main

import "fmt"

func main() {
	const (
		Low = iota
		Mid
		High
	)
	fmt.Println(Low)
	fmt.Println(Mid)
	fmt.Println(High)
}

Doubling with a shift

The expression 1 << iota doubles at each step. The three names print as 1, 2, and 4.

package main

import "fmt"

func main() {
	const (
		Read = 1 << iota
		Write
		Exec
	)
	fmt.Println(Read)
	fmt.Println(Write)
	fmt.Println(Exec)
}

A value with a label

A hand-written label prints beside the chosen value. The word names the size, and the number comes from the enum.

package main

import "fmt"

func main() {
	const (
		Small = iota
		Medium
		Large
	)
	size := Medium
	fmt.Println("Medium:", size)
}

Example

package main

import "fmt"

func main() {
	const (
		Tiny = iota
		Regular
		Grand
	)
	fmt.Println("Tiny:", Tiny)
	fmt.Println("Regular:", Regular)
	fmt.Println("Grand:", Grand)
}

Key points

  • Use an enum to give clear names to a small set of numbers.
  • iota is a counter that starts at 0 inside a const block.
  • Each next name in the block raises iota by 1.
  • An enum value is a plain whole number once the program runs.

In this example, the const block names three sizes with iota. Tiny holds 0, Regular holds 1, and Grand holds 2. Each print line pairs a size value with a hand-written label.

Note

Go has no enum keyword. A const block with iota does the job.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Go Playground

Exercise

A const block starts with First = iota and names two more values below it. What numbers do the three names hold?