How to parse a string and change certain characters?

Question

go

Hello! There is such a question:
How can a string be parsed and replace certain characters. For example:
Given: [phone] or +999 (99) -999-99-99
Need to be: [phone].
I'm a beginner, so I can explain more easily.

Answer 1

Without regular expressions:
https://play.golang.org/p/SIqQunrMQHI

import (
  "strings"
)

func normalize(s string) string {
  var sb strings.Builder

  for _, r := range s {
    switch {
    case '0' <= r && r <= '9':
    case r == '+':
    default:
      continue
    }
    sb.WriteRune(r)
  }

  return sb.String()
}

With regulars:
https://play.golang.org/p/GYzsCTaEa9W

import (
  "regexp"
  "strings"
)
var re = regexp.MustCompile(`(?i)[\d\+]+`)

func normalize(s string) string {
  var sb strings.Builder
  subs := re.FindAllStringSubmatch(s, -1)
  
  for _, sub := range subs {
    sb.WriteString(sub[0])
  }
  
  return sb.String()
}

Or a variant with the replacement of characters:

var re = regexp.MustCompile(`(?m)[^+\d]`)
var str = `[phone]`
fmt.Println(re.ReplaceAllString(str, ""))

The version without regular expressions is more economical in terms of processor and memory resources, but if the pattern changes, it will also require changing the function code.

Answer 2

Replace spaces with "blank".
https://golang.org/pkg/strings/#ReplaceAll
strings.ReplaceAll("[phone]", " ", "")