proposal: strings: add Lines

[icholy]

If I already have a string in memory, there's no simple and efficient way of splitting it into lines.

The naïve approach won't handle \r\n.

strings.Split(s, "\n")

Using a bufio.Scanner works but it creates copies instead of slicing the existing string.

var lines []string
sc := bufio.NewScanner(strings.NewReader(s))
for sc.Scan() {
    lines = append(lines, sc.Text())
}

I'd like a new strings.Lines function similar to strings.Fields for this use-case.

[icholy]

Here are some other approaches I've seen while searching:

strings.Split(strings.ReplaceAll(s, "\r\n", "\n"), "\n")

regexp.MustCompile("\r?\n").Split(s, -1)

[ALTree]

Assuming a "line" is anything delimited by one of \n, \r, and \r\n, calling strings.FieldsFunc with func(c rune) bool { return c == '\n' || c == '\r' } seems to work.

[icholy]

@ALTree thanks, I'll be using that. However, it doesn't give the correct output for strings with blank lines like "\n\n\n"

[ALTree]

Oh, right. It's actually just Fields. You want something that returns 4 strings for "text\n\n\ntext`, two of which are empty, which is different from what Fields does.

[ALTree]

What about adding strings.SplitFunc instead? That would mirror strings.FieldsFunc and let you split on a custom function.

[icholy]

What would the signature of the callback look like? Something like func(rune) bool wouldn't be able to handle the \r\n case.

[ALTree]

EDIT: right, that's probably why it doesn't exist. The API is less obvious. You'd need to check substrings instead of the single runes.

[icholy]

If something like SplitMulti was added, then you'd also need all the different variations. That gets messy.

func SplitMulti(s, seps []string) []string
func SplitMultiAfter(s, seps []string) []string
func SplitMultiAfterN(s, seps []string, n int) []string
func SplitMultiN(s, seps []string, n int) []string

[rsc]

Cut works great.

for text != "" {
   line, rest, ok := strings.Cut(text, "\n")
   text = rest
   line = strings.TrimSuffix(line, "\r") // if you care
   ... use line ...
}

[rsc]

For that matter, strings.SplitAfter(text, "\n") also works.
There's an extra empty string at the end of the slice if the text ends in a final \n (as most do).

[rsc]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group