转到：用正则表达式交换大小写

I want to swap cases using regexp in Go. I tried to use the similar method in Javascript but I can't figure out how to make Go understand $ sign.

func swapcase(str string) string {
    var validID = regexp.MustCompile(`[A-Z]`)
    return validID.ReplaceAllString(str, strings.ToLower(str))

/*
 var validID = regexp.MustCompile(`[a-z]`)
 return validID.ReplaceAllString(str, strings.ToUpper(str))
*/
}

This was my try. It works for converting all upper to lower, and vice versa, but what I want to do is to swap every letter at the same time. For example, "Hello" ---> "hELLO"

And the following is my code in Javascript that works perfect.

 function SwapCase(str) {

     return str.replace(/([a-z])|([A-Z])/g,
        function($0, $1, $2) {
            return ($1) ? $0.toUpperCase() : $0.toLowerCase();
        })
 }

You can't (I think) do this with a regexp, but it's straightforward with strings.Map.

package main

import (
    "fmt"
    "strings"
)

func swapCase(r rune) rune {
    switch {
    case 'a' <= r && r <= 'z':
        return r - 'a' + 'A'
    case 'A' <= r && r <= 'Z':
        return r - 'A' + 'a'
    default:
        return r
    }
}

func main() {
    s := "helLo WoRlD"
    fmt.Println(strings.Map(swapCase, s))
}