使用数字文字但不使用数字常量的移位运算符出错

Question

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

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

当我将班次计数声明为常量时，班次运算符起作用了。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)
}

为什么常量有效而文字对移位运算符无效？

Answer 1

使用 math/bits 包你可以这样做：

package main

import (
    "fmt"
    "math/bits"
)

func main() {
    bucketCntBits := 3
    bucketCnt     := bits.RotateLeft(1, bucketCntBits)
    fmt.Println("Hello, playground", bucketCnt)
}

https://play.golang.org/p/fVK2xysL896

Answer 2

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.

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

这不再是 Go 1.13（2019 年 9 月）及更高版本的错误。

你的榜样，

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

Answer 3

或者，您可以将类型 uint8、uint16、uint32 或 uint64 转换为整数文字。例如，

func main() {
    bucketCntBits := uint32(3)
    bucketCnt     := 1 << bucketCntBits
    fmt.Println(bucketCnt)
}

输出：

使用数字文字但不使用数字常量的移位运算符出错

Error in shift operator using numeric literals but not with numeric constant

constants

literals

go