Vfrdtyky

In Ruby, you can encode string to ASCII as follows:

str.force_encoding('ASCII')

How can we achieve the same in Go?

strconv.QuoteToASCII

QuoteToASCII returns a double-quoted Go string literal representing s. The returned string uses Go escape sequences (t, n, xFF, u0100) for non-ASCII characters and non-printable characters as defined by IsPrint.

Or if you want an array of ascii codes, you could do

import "encoding/ascii85"

dst := make(byte, 25, 25)

dst2 := make(byte, 25, 25)

ascii85.Encode(dst, byte("Hello, playground"))

fmt.Println(dst) 

ascii85.Decode(dst2, dst, false)

fmt.Println(string(dst2))

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

A simple version that omits invalid runes could look like this:

func forceASCII(s string) string {

  rs := make(rune, 0, len(s))

  for _, r := range s {

    if r <= 127 {

      rs = append(rs, r)

    }

  }

  return string(rs)

}

// forceASCII("Hello, World!") // => "Hello, World!"

// forceASCII("Hello, 世界!") // => "Hello, !"

// forceASCII("Привет") // => ""

But what if you want special behavior if the target UTF-8 string contains any characters outside the ASCII character range of [0,127]?

You could write a function that handles various cases by extracting a function argument which takes the invalid-ASCII rune and returns a string replacement or error.

For example (Go Playground):

func forceASCII(s string, replacer func(rune) (string, error)) (string, error) {

  rs := make(rune, 0, len(s))

  for _, r := range s {

    if r <= 127 {

      rs = append(rs, r)

    } else {

      replacement, err := replacer(r)

      if err != nil {

        return "", err

      }

      rs = append(rs, rune(replacement)...)

    }

  }

  return string(rs), nil

}



func main() {

  replacers := func(r rune) (string, error){

    // omit invalid runes

    func(_ rune) (string, error) { return "", nil },

    // replace with question marks

    func(_ rune) (string, error) { return "?", nil },

    // abort with error */

    func(r rune) (string, error) { return "", fmt.Errorf("invalid rune 0x%x", r) },

  }



  ss := string{"Hello, World!", "Hello, 世界!"}

  for _, s := range ss {

    for _, r := range replacers {

      ascii, err := forceASCII(s, r)

      fmt.Printf("OK: %q → %q, err=%vn", s, ascii, err)

    }

  }

  // OK: "Hello, World!" → "Hello, World!", err=<nil>

  // OK: "Hello, World!" → "Hello, World!", err=<nil>

  // OK: "Hello, World!" → "Hello, World!", err=<nil>

  // OK: "Hello, 世界!" → "Hello, !", err=<nil>

  // OK: "Hello, 世界!" → "Hello, ??!", err=<nil>

  // OK: "Hello, 世界!" → "", err=invalid rune 0x4e16

}