type Weekday int
const (
Sunday Weekday = iota // 0
Monday // 1
Tuesday // 2
Wednesday // 3
Thursday // 4
Friday // 5
Saturday // 6
)
func (day Weekday) String() string {
names := [...]string{
"Sunday",
"Monday",
"Tuesday",
"Wednesday",
"Thursday",
"Friday",
"Saturday",
}
if day < Sunday || day > Saturday {
return "Unknown"
}
return names[day]
}
type FileSizeUnit int
const (
_ = iota // 忽略第一个值 0,让后续常量从 1 开始递增
KB FileSizeUnit = 1 << (10 * iota) // 1 << (10*1) = 1 << 10 = 1024
MB // 1 << (10*2) = 1 << 20 = 1048576
GB // 1 << (10*3) = 1 << 30 = 1073741824
TB // 1 << (10*4) = 1 << 40 = 1099511627776
)
package main
import "fmt"
func main() {
{
const (
a = iota
b
c
)
fmt.Printf("%+v\n", []int{a, b, c})
// [0 1 2]
}
{
const (
a = 1
b = iota
c
)
fmt.Printf("%+v\n", []int{a, b, c})
// [1 1 2]
}
{
const (
a = 1
b = 2
c = iota
)
fmt.Printf("%+v\n", []int{a, b, c})
// [1 2 2]
}
{
const (
a = 1
b = iota
c = iota
)
fmt.Printf("%+v\n", []int{a, b, c})
// [1 1 2]
}
}
总结
- 首次出现是这个常量块中变量的顺序(0 开始)
- 后面的常量如果没有定义,就表示是按照前面的常量定义来,只是 iota 代表的值 + 1 了
- 如果想跳过一个值,可以使用下划线