Is there a good way to test a string against a ser...

# announcements

[nkiesel]

Is there a good way to test a string against a series of regex without matching twice? Right now I have

for (line in lines) {
   if (Regex("#(.) A (.+)").matches(line)) {
       val m = Regex("#(.) A (.+)").matchEntire(line)
        ...
   } else if (Regex("#(.) B (.+)").matches(line)) {
       val m = Regex("#(.) B (.+)").matchEntire(line)
       ...
   }
}

(real code of course has regexes defined only once etc.). I now changed it to

for (line in lines) {
   val m1 = Regex("#(.) A (.+)").matchEntire(line)
   if (m1 != null) {
      ...
      continue
   }
   val m2 = Regex("#(.) B (.+)").matchEntire(line)
   if (m2 != null) {
      ...
      continue
   }
}

but that does not look too nice (esp. the need for repeated continue)

[nanodeath]

can you edit in more newlines? it's kinda impossible to read

[nanodeath]

but also matchEntire already returns null if there's no match

[nanodeath]

...and also you're constructing each Regex object from scratch for every line

[nkiesel]

Regex from scratch: that is just here to keep the sample smaller. Real code has that extracted.

[nkiesel]

Ideally I would like to have a when which understands regex and injects the MatchResult into the block

when (line) {
   Regex("A(.+)") -> println(it.groupValues[1])
    Regex("B(.)(.+)") -> println(it.groupValues[2])
}

(i.e. here it would refer to the MatchResult)

[nanodeath]

sounds Perl/Ruby-ish 🙂

running through some examples in my head...I don't think you can avoid a continue. if you use pattern.match()?.let, you'd need a continue

[nanodeath]

there might be some sequenceOf({ performMatch }).firstNotNull() trickery you could do but I don't think it's worth it

[Nir]

It really depends how much you care, I thought about this problem a bit before when i was comparing python and kotlin, and looking at walrus operator use cases in python, one of the examples was similar to this

[Nir]

If you care enough then you can write a function that would do something like this:

firstMatchEntire(line,
    Regex("#(.) A (.+)") to { .... },
    Regex(...) to { ... }
)

[Nir]

and so on

[nanodeath]

also, might not be possible, but perhaps you can simply combine the regexes into one larger regex

[ephemient]

this is possible:

regex1.matchEntire(line)?.also { match ->
} ?: regex2.matchEntire(line)?.also { match ->
} ?: regex3.matchEntire(line)?.also { match ->
} // etc.

[ephemient]

this is a case where Scala's pattern matching and destructuring works well, but it needs more design work to get into Kotlin. https://youtrack.jetbrains.com/issue/KT-186