Range

For slice or map

The range form of the for loop iterates over a slice or map.

When ranging over a slice, two values are returned for each iteration. The first is the index, and the second is a copy of the element at that index.

Example

package main

import "fmt"

var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}

func main() {
	for i, v := range pow {
		// i is current index, v is current value
		fmt.Printf("2**%d = %d\n", i, v)
	}
}

2**0 = 1
2**1 = 2
2**2 = 4
2**3 = 8
2**4 = 16
2**5 = 32
2**6 = 64
2**7 = 128

Skip or Omit

The index or value can be skipped by assigning to _.

for i, _ := range pow
for _, value := range pow

If you only want the index, you can omit the second variable.

for i := range pow

Example

package main

import "fmt"

func main() {
    pow := make([]int, 6)
    for i := range pow {
        // same as 2**i
        pow[i] = 1 << uint(i)
    }
    for _, value := range pow {
        fmt.Printf("%d\n", value)
    }
}

1
2
4
8
16
32