Break

Sometimes in Go programs we need to exit a loop early, without running any further iterations. The break statement can be used to terminate the loop.

With a break with no label, we can exit the immediately enclosing loop. With a label, it is possible to exit multiple nested enclosing loops at once.

Example

This program loops over elements in a slice with a for-loop. The string "frog" is considered a sentinel element, and we terminate the loop with a break when it is encountered.

Part 1 We create a slice of 3 strings, and the string "frog" is the second element in the slice.

Part 2 With a for-range loop, we enumerate the elements of the slice and print them to the console.

Part 3 If an element with the value "frog" is encountered, we exit the loop with a break statement.

package main

import "fmt"

func main() {
    // Part 1: create a slice of 3 strings.
    animals := []string{"bird", "frog", "dog"}

    // Part 2: loop over the slice of strings, and print each string element.
    for _, animal := range animals {
        fmt.Println(animal)

        // Part 3: if the string is "frog", break the loop.
        if animal == "frog" {
            break
        }
    }
}bird
frog

Label

With a label, it is possible to use the break keyword to stop executing a loop that contains the enclosing loop. We do not need to set boolean flags and have multiple break statements.

Part 1 We have a label called "Outer" that is for the top-level for-loop. Each loop iterates over 10 integers.

Part 2 If this condition is true, we break both the inner and the outer loop with a labeled break statement.

package main

import "fmt"

func main() {
    // Part 1: specify a label for the outer loop, and then use 2 nested loops.
    Outer:
    for i := range 10 {
        for b := range 10 {
            // Part 2: if the inner variable is 5, terminate both the inner and outer loops with a break.
            if b == 5 {
                break Outer
            }
            fmt.Println(i, b)
        }
    }
}0 0
0 1
0 2
0 3
0 4

Break, return

If the loop we want to break is in a separate method, we can often use a return statement instead of a break statement.

package main

import "fmt"

func Example() {
    word := "abc"
    for _, r := range word {
        if r == 'c' {
            // The return keyword could be used instead of break here.
            break
        }
        fmt.Println(r)
    }
}

func main() {
    Example()
}97
98

With the break keyword, we have a standard way to exit the enclosing loop in a Go program. Other keywords, such as continue or return, can fill similar requirements.