So I apparently suck at regexes. I'm trying to come with the simplest regex based alternative (due to a spec out of my control) to

substringAfter()

What would the kotlin regex based alternative to

substringAfter("abc")

be for example?

I think

.*abc(.*)

and then get the first group

I would use

(?<=abc).*

for substring after

abc

. (At least on JVM.) UPD. It works on JS, as well.

Using positive lookbehind, as Gleb suggested:

fun String.reinventedSubstringAfter(delimiter: String) =
    "(?<=$delimiter).*".toRegex().find(this)?.value ?: this

(assuming the delimiter doesn't contain any special characters). You might want to drop the

?: this

at the end, if you want it to return null if it doesn't find the substring. I put it in there to make it compatible with the standard

substringAfter

which returns the original string.

FWIW This was the closest I could get

fun findThing(chars: String, line: String): String? {
    val matcher = Pattern.compile(".*$chars(.*)").matcher(line)
    if (matcher.matches()) {
      return matcher.group(1)
    }
    return null
  }

This is a brilliant tool: https://regex101.com/ − but it does lack the ability to say «listen, your regex is OK, but here's a more efficient one (or a more readable one): ---»

You're not the only one that suck with regex, in my case I use ChatGPT to generate the regex and test the result using regex101 😅

I feel like I can sometimes get a regex together, but the regex apis always mess me up. It seems like theres so many ways for a regex and matchers. just makes my head hurt.