带有反向引用的golang regexp ReplaceAllStrings不太起作用

Question

Trying to capitalize each letter at begin of the word. I know that there is strings.Title, but that is too imprecise for my needs.

I am not sure why this does not work:

package main

import (
    "fmt"
    "regexp"
    "strings"
)

func main() {
    re := regexp.MustCompile(`\b([a-z])`)
    fmt.Println(re.ReplaceAllString("my test string", strings.ToUpper("$1")))

}

https://play.golang.org/p/C-8QG1FrOi

Answer 1

You should use ReplaceAllStringFunc, example:

re.ReplaceAllStringFunc("my test string", func(s string) string {
                                          return strings.ToUpper(s)})

See working demo.

Your code doesn't work because:

re.ReplaceAllString("my test string", strings.ToUpper("$1"))

is the same as:

re.ReplaceAllString("my test string", "$1")

since the upper case of $1 is still $1.