I need to split a string by a separator but don't want to split if the separator is prefixed by the escape string.

For example:

"This works\\ but it\\ isn't pretty." with " " as the separator and "\\" as the escape string should produce the following: []string{"This", "works but", "it isn't", "pretty."}

I wrote the following code for it:

func SplitWithEscaping(s string, separator string, escapeString string) []string {
    untreated := strings.Split(s, separator)
    toReturn := make([]string, 0, len(untreated))
    for i := 0; i < len(untreated); i++ {
        next, ii := t(untreated, i, separator, escapeString)
        i = ii - 1
        toReturn = append(toReturn, strings.ReplaceAll(next, escapeString+separator, separator))
    return toReturn

func t(stringSlice []string, i int, seperator, escapeString string) (string, int) {
    if !strings.HasSuffix(stringSlice[i], escapeString) {
        return stringSlice[i], i + 1
    next, ii := t(stringSlice, i+1, seperator, escapeString)
    return stringSlice[i] + seperator + next, ii

This is the playground link for my working code: https://play.golang.org/p/jfHFt9_vtE7

How can I make my code prettier but also more performant?

  • \$\begingroup\$ does your code work ? \$\endgroup\$ Apr 9 at 18:10
  • 1
    \$\begingroup\$ yes, it does. Otherwise I would have posted it on stackoverflow. (No offence) \$\endgroup\$
    – Cookie04
    Apr 9 at 18:14

One approach that's simple, but is a bit of a dirty trick: first replace sequences of escape+separator with a string that's never going to occur in your text (for example a NUL byte "\x00"), then do the split, then do the reverse replace on each token. For example (Go Playground link):

func SplitWithEscaping(s, separator, escape string) []string {
    s = strings.ReplaceAll(s, escape+separator, "\x00")
    tokens := strings.Split(s, separator)
    for i, token := range tokens {
        tokens[i] = strings.ReplaceAll(token, "\x00", separator)
    return tokens

Your approach of splitting and then re-joining if the last character was an escape works, but it's a bit tricky, and it does more work than necessary. You may also want to name the t function a bit more meaningfully.

An alternative approach would be more of a tokenizer, where you loop through all the bytes in the string, looking for escape and space. Here's the code for that, but note that I've made the separator and escape a single byte to simplify it -- I'm guessing they will be in most cases anyway (Go Playground link):

func SplitWithEscaping(s string, separator, escape byte) []string {
    var token []byte
    var tokens []string
    for i := 0; i < len(s); i++ {
        if s[i] == separator {
            tokens = append(tokens, string(token))
            token = token[:0]
        } else if s[i] == escape && i+1 < len(s) {
            token = append(token, s[i])
        } else {
            token = append(token, s[i])
    tokens = append(tokens, string(token))
    return tokens

The other approach that came to mind is regexes, but you have to be able to say "match space, but only if it's not preceded by this escape", which I think you can only do with lookbehind expressions like ?<, and Go's regexp package doesn't support those.


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