例如，ILen和XLen，

package main

import "fmt"

const (
    I1 = 1 << iota
    I2
    I3
    ILen int = iota
)

const (
    X1       = "A"
    X2       = "B"
    X3       = "C"
    XLen int = iota
)

func main() {
    fmt.Println(I1, I2, I3, ILen)
    fmt.Println(X1, X2, X3, XLen)
}

https://go.dev/play/p/krBVid3jLNq
The Go Programming Language Specification
伊奥塔
在常量声明中，预先声明的标识符iota表示连续的无类型整型常量。它的值是该常量声明中相应ConstSpec的索引，从零开始。