Go Range

range 关键字用于在 for 循环中迭代数组、切片、通道或映射项。对于数组和切片，它返回项的索引作为整数。对于映射，它返回下一个键值对的键。Range可以返回一个值或两个值。如果在range表达式的左边只使用一个值，那么它就是下表中的第一个值。

Range expression	1st Value	2nd Value(Optional)
Array or slice a [n]E	index i int	a[i] E
String s string type	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

示例

以下段落展示了如何使用范围-

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*/
   countryCapitalMap := 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)
   }
}

当以上代码被编译并执行时，会产生以下结果 –

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