range关键字用于循环遍历数组，切片，管道或映射项目。数组和切片，它返回项目作为整数的索引。映射返回下一个键 - 值对的键。无论是范围返回一个或两个值。如果只有一个值被用于在一系列表达式的左侧，它是下表中的第一值。

范围表达式	第一个值	第二个值(Optional)
数组或切片 a [n]E	index i int	a[i] E
String s 字符串类型	index i int	rune int
map m map[K]V	key k K	value m[k] V
channel c chan E	element e E	none

例子

下面是一个例子：

package main

import "fmt"

func main {
   /* create a slice */
   numbers := []int{0,1,2,3,4,5,6,7,8} 
   
   /* print the numbers */
   for i:= range numbers {
      fmt.Println("Slice item",i,"is",numbers[i])
   }
   
   /* create a map*/
   coutryCapitalMap := map[string] string {"France":"Paris","Italy":"Rome","Japan":"Tokyo"}
   
   /* print map using keys*/
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }
   
   /* print map using key-value*/
   for country,capital := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",capital)
   }
}

当上述代码被编译和执行时，它产生了以下结果：

Slice item 0 is 0
Slice item 1 is 1
Slice item 2 is 2
Slice item 3 is 3
Slice item 4 is 4
Slice item 5 is 5
Slice item 6 is 6
Slice item 7 is 7
Slice item 8 is 8
Capital of France is Paris
Capital of Italy is Rome
Capital of Japan is Tokyo
Capital of France is Paris
Capital of Italy is Rome
Capital of Japan is Tokyo