3. for range

for range 可以用于遍历数组、切片、字符串、map及通道， 类似其他的语言中的foreach语句。

for key, value := range []int{1, 2, 3, 4} {
    fmt.Printf("key:%d  value:%d\n", key, value)
}

m := map[string]int{
    "hello": 100,
    "world": 200,
}
for key, value := range m {
    fmt.Println(key, value)
}

c := make(chan int)
go func() {
    c <- 1
    c <- 2
    c <- 3
    close(c)
}()
for v := range c {
    fmt.Println(v)
}