正则表达式“不是常量” Golang出错 [英] Regex "is not a constant" error in Golang

问题描述

我试图在Golang中编写一个正则表达式来验证一个字符串只有字母数字，句点和下划线。然而，我遇到了一个我从未见过的错误，并且在谷歌搜索中一直没有成功。

这是正则表达式：

  pattern = regexp.MustCompile（`^ [A-Za-z0-9_\。] +`）
  
 
 
这是错误：
 
 
  const initializer regexp .MustCompile（^ [A-Za-z0-9_\\。] +）不是常量
  
不是常数是什么意思，我该如何解决这个问题？
 
谢谢。
解决方案
当你试图分配一个不能保持常量的类型的变量时（例如， Regexp ），通常会发生这种情况。 。只有像 int ， string 等基本类型可以是常量。详情请参阅 。
 
 
 示例：
 
 
  pattern = regexp.MustCompile（`^ [A-Za-z0-9_\。] + `）
 //转换为：
 const pattern = regexp.MustCompile（`^ [A-Za-z0-9_\。] +`）
  
您必须声明它为 var 才能工作：
  var pattern = regexp.MustCompile（`^ [A-Za-z0-9_\。] +`）
  
另外，我通常会把一个音符说成是一个常量： 
 
 
  var / * const * / pattern = regexp.MustCompile（`^ [A-Za-z0-9_\。] +`）
  
 
I'm trying to write a regex in Golang to verify that a string only has alphanumerics, periods, and underscores. However, I'm running into an error that I haven't seen before and have been unsuccessful at Googling.


Here's the regex:
pattern = regexp.MustCompile(`^[A-Za-z0-9_\.]+`)
Here is the error:
const initializer regexp.MustCompile("^[A-Za-z0-9_\\.]+") is not a constant
What does "not a constant" mean and how do I fix this?

Thanks.
解决方案
This typically happens when you're trying to assign to a package-level variable that has a type that can't be constant (like for example, Regexp). Only basic types likes int, string, etc. can be constant. See here for more details.

Example:
pattern = regexp.MustCompile(`^[A-Za-z0-9_\.]+`)
// which translates to:
const pattern = regexp.MustCompile(`^[A-Za-z0-9_\.]+`)
You have to declare it as a var for it to work:
var pattern = regexp.MustCompile(`^[A-Za-z0-9_\.]+`)
In addition, I usually put a note to say that the variable is treated as a constant:
var /* const */ pattern = regexp.MustCompile(`^[A-Za-z0-9_\.]+`)


                        
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