Go中的iota

package main
import "fmt"
const a0 = iota // a0 = 0  // const出现, iota初始化为0
const (
  a1 = iota // a1 = 0   // 又一个const出现, iota初始化为0
  a2 = iota // a2 = 1   // const新增一行, iota 加1
  a3 = 6    // a3 = 6   // 自定义一个常量
  a4        // a4 = 6   // 不赋值就和上一行相同
  a5 = iota // a5 = 4   // const已经新增了4行, 所以这里是4
)
const (
  b = iota // b = 0
  c        // c = 1
  d = 1111
  e
  f = iota
)
const (
  TestMin = -1
  TestA
  TestB = iota
  TestC
)
func main() {
  fmt.Println("a0:", a0)
  fmt.Println("a1:", a1)
  fmt.Println("a2:", a2)
  fmt.Println("a3:", a3)
  fmt.Println("a4:", a4)
  fmt.Println("a5:", a5)
  fmt.Println("---------")
  fmt.Println("b is:", b)
  fmt.Println("c is:", c)
  fmt.Println("d is:", d)
  fmt.Println("e is:", e)
  fmt.Println("f is:", f)
  fmt.Println("---------")
  fmt.Println("TestMin:", TestMin)
  fmt.Println("TestA:", TestA)
  fmt.Println("TestB:", TestB)
  fmt.Println("TestC:", TestC)
}

a0: 0
a1: 0
a2: 1
a3: 6
a4: 6
a5: 4
---------
b is: 0
c is: 1
d is: 1111
e is: 1111
f is: 4
---------
TestMin: -1
TestA: -1
TestB: 2
TestC: 3

package main
import "fmt"
// 跳值使用iota使用_来达到目的：
const (
  h = iota // 0
  i = iota // 1
  _
  k = iota // 3
)
// 当常量表达式为空时，会自动继承上一个存在非空的表达式。
const (
  x = iota * 2
  y
  z
)
func main() {
  fmt.Println(h)
  fmt.Println(i)
  fmt.Println(k)
  fmt.Println("-------")
  fmt.Println(x)
  fmt.Println(y)
  fmt.Println(z)
}

0
1
3
-------
0
2
4

package main
import "fmt"
type OrderState uint8
const (
  // 0-待支付
  WaitPay OrderState = iota
  // 1-支付中
  Paying
  // 2-支付成功
  PaySucc
  // 3-支付失败
  PayFail
)
// 对应于xx表is_show字段
const (
  _       uint8 = iota
  Show          // 1-显示
  NotShow       // 2-不显示
)
func main() {
  fmt.Println(PaySucc)
  fmt.Println(Show)
}

2
1

package main
import (
  "fmt"
)
const (
  i = 1 << iota
  j = 3 << iota
  k
  l
)
func main() {
  fmt.Println("i=", i)
  fmt.Println("j=", j)
  fmt.Println("k=", k)
  fmt.Println("l=", l)
}

i= 1
j= 6
k= 12
l= 24

    i=1<<iota
    j=3<<iota
    k
    l

    i=1<<0
    j=3<<1
    k=3<<2
    l=3<<3

package main
import "fmt"
func main() {
  const (
    IgEggs         = 1 << iota // 1 << 0 which is 00000001
    IgChocolate                // 1 << 1 which is 00000010
    IgNuts                     // 1 << 2 which is 00000100
    IgStrawberries             // 1 << 3 which is 00001000
    IgShellfish                // 1 << 4 which is 00010000
  )
  fmt.Println(IgEggs, IgChocolate, IgNuts, IgStrawberries, IgShellfish)
}

package main
import "fmt"
type ByteSize int64
const (
  _           = iota             // ignore first value by assigning to blank identifier
  KB ByteSize = 1 << (10 * iota) // 1 << (10*1)
  MB                             // 1 << (10*2)
  GB                             // 1 << (10*3)
  TB                             // 1 << (10*4)
  PB                             // 1 << (10*5)
  EB                             // 1 << (10*6)
  //ZB                             // 1 << (10*7)
  //YB                             // 1 << (10*8)
)
func main() {
  fmt.Printf("KB= %d Byte\n", KB)
  fmt.Printf("MB= %d Byte\n", MB)
  fmt.Printf("GB= %d Byte\n", GB)
}

KB= 1024 Byte
MB= 1048576 Byte
GB= 1073741824 Byte