The switch Statement

Basic switch

A switch compares an expression against a series of case values and runs the matching branch's code, then automatically stops -- there is no implicit fallthrough to the next case, which is a common point of confusion for people coming from C or Java.

Example: Basic switch

package main

import "fmt"

func main() {
	day := "Tue"
	switch day {
	case "Mon":
		fmt.Println("Start of week")
	case "Tue", "Wed", "Thu":
		fmt.Println("Midweek")
	default:
		fmt.Println("Other day")
	}
}

switch with No Expression

Omitting the expression after switch turns each case into a boolean condition, evaluated in order, functioning like a tidier version of a chain of else-if statements.

Note: This form reads more cleanly than a long if/else-if chain when there are several conditions.

Example: switch with No Expression

package main

import "fmt"

func main() {
	score := 82
	switch {
	case score >= 90:
		fmt.Println("A")
	case score >= 75:
		fmt.Println("B")
	default:
		fmt.Println("C")
	}
}

Using fallthrough

If you do want a case to continue into the next one, Go requires you to say so explicitly with the fallthrough keyword, making the (unusual) behavior visible in the code rather than an easy-to-miss default.

Note: fallthrough is rarely needed -- reach for it only when you deliberately want the next case's code to also run.

Example: Using fallthrough

package main

import "fmt"

func main() {
	n := 1
	switch n {
	case 1:
		fmt.Println("one")
		fallthrough
	case 2:
		fmt.Println("two (via fallthrough)")
	case 3:
		fmt.Println("three")
	}
}

switch with an Init Statement

Just like if, a switch can run a short statement before the value it switches on, scoping a variable to the whole switch block -- handy for computing a value once and branching on it.

Example: switch with an Init Statement

package main

import "fmt"

func classify(n int) string {
	switch remainder := n % 3; remainder {
	case 0:
		return "divisible by 3"
	default:
		return "not divisible by 3"
	}
}

func main() {
	fmt.Println(classify(9))
	fmt.Println(classify(10))
}