learn/golang-learn/06-constants_iota/constants_iota.go

// iota_cheatsheet.go
package main

import "fmt"

/*
	-------------------------------------------------
	  1) 顺序枚举（最常用）
	     Sunday=0, Monday=1, ..., Saturday=6

-------------------------------------------------
*/
const (
	Sunday = iota // 0
	Monday        // 1
	Tuesday
	Wednesday
	Thursday
	Friday
	Saturday
)

/*
	-------------------------------------------------
	  2) 位掩码（flags）
	     每个常量占 1 个二进制位，可用于权限/选项

-------------------------------------------------
*/
const (
	Read  = 1 << iota // 0b0001
	Write             // 0b0010
	Exec              // 0b0100
)

/*
	-------------------------------------------------
	  3) 自定义步长或公式
	     生成 1KB, 1MB, 1GB ... 的精确字节数

-------------------------------------------------
*/
const (
	_  = iota             // 0 丢掉
	KB = 1 << (10 * iota) // 1 << 10  = 1024
	MB                    // 1 << 20  = 1048576
	GB                    // 1 << 30  = 1073741824
)

/*
	-------------------------------------------------
	  4) 跳号 + 中途改公式
	     演示跳过某个值、后续再换算法

-------------------------------------------------
*/
const (
	A = iota      // 0
	B             // 1
	_             // 2 被跳过
	C             // 3
	D = iota + 10 // 4+10 = 14
	E             // 5+10 = 15
)

func main() {
	fmt.Println("Weekday:", Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday)
	fmt.Println("Flags  :", Read, Write, Exec)
	fmt.Println("Storage:", KB, MB, GB)
	fmt.Println("Misc   :", A, B, C, D, E)
}