Range over built in types

Context

The range keyword allows iteration over slices, arrays, maps, strings (runes), and channels. It returns one or two values depending on the type.

• Slices/arrays: index, value
• Maps: key, value
• Strings: byte index, rune
• Channels: value (single parameter)

Example

Iterate over a slice, a map, and a string.

Code example

package main

import "fmt"

func main() {
    // Slice
    nums := []int{2, 4, 6}
    for i, v := range nums {
        fmt.Printf("index=%d, value=%d\n", i, v)
    }

    // Map
    colors := map[string]string{"red": "#FF0000", "green": "#00FF00"}
    for key, value := range colors {
        fmt.Printf("%s -> %s\n", key, value)
    }

    // String (rune by rune)
    for pos, r := range "Hello, 世界" {
        fmt.Printf("%d: %c\n", pos, r)
    }
}

Output

index=0, value=2
index=1, value=4
index=2, value=6
red -> #FF0000
green -> #00FF00
0: H
1: e
2: l
3: l
4: o
5: ,
6:
7: 世
10: 界

Useful links

• Go spec: Range clause
• Go by Example: Range