go - 使用数字文字但不使用数字常量的移位运算符会出错

Question

我在 go with invalid operation: 1 << bucketCntBits (shift count type int, must be unsigned integer) 中执行移位操作时遇到错误尝试在 go inside 中声明文字时出错 main() body 失败的文字示例:https://play.golang.org/p/EqI-yag5yPp

func main() {
    bucketCntBits := 3 // <---- This doesn't work
    bucketCnt     := 1 << bucketCntBits
    fmt.Println("Hello, playground", bucketCnt)
}

当我将移位计数声明为常量时，移位运算符将起作用。 工作常数示例:https://play.golang.org/p/XRLL4FR8ZEl

const (
    bucketCntBits = 3 // <---- This works
)

func main() {

    bucketCnt     := 1 << bucketCntBits
    fmt.Println("Hello, playground", bucketCnt)
}

为什么常量可以工作，而文字对于移位运算符却不起作用？

Answer 1

Go 1.13 Release Notes (September 2019)

Changes to the language

Per the signed shift counts proposal Go 1.13 removes the restriction that a shift count must be unsigned. This change eliminates the need for many artificial uint conversions, solely introduced to satisfy this (now removed) restriction of the << and >> operators.

<小时/>

invalid operation: 1 << bucketCntBits (shift count type int, must be unsigned integer)

对于 Go 1.13(2019 年 9 月)及更高版本，这不再是错误。

你的例子，

package main

import "fmt"

func main() {
    bucketCntBits := 3
    bucketCnt := 1 << bucketCntBits
    fmt.Println(bucketCnt)
}

输出:

$ go version
go version devel +66ff373911 Sat Aug 24 01:11:56 2019 +0000 linux/amd64

$ go run shift.go
8