How to use scala.util.matching.Regex correctly?

Question

This may look obvious but I couldn't explain the No match available error . Below, you find a definition of a simple matching function I am using.

The same instructions inside the function run without an issue, however calling the function raises the error. Can you help me pinpoint the mistake ?

import scala.util.matching.Regex

def regexParsing(inputRecord:String, inputRegex:String, listOfFields:Seq[String], fieldsToRemove:Seq[String]): scala.collection.Map[String,Any] = {
    val logPattern = new Regex(inputRegex, listOfFields:_*)
    val result = logPattern.findAllIn(inputRecord)
    val resultMap = result.groupNames.map(a => Map(a.toString -> result.group(a))).reduce(_++_)
    return resultMap
}

val inputRecord = """s2222f"""
val inputRegex = """(.*)"""
val listOfFields = Seq("field")
val fieldsToRemove = Seq("field1", "field2")

// working 
val logPattern = new Regex(inputRegex, listOfFields:_*)
val result = logPattern.findAllIn(inputRecord)
val resultMap = result.groupNames.map(a => Map(a.toString -> result.group(a))).reduce(_++_)

// not working 
regexParsing(inputRecord, inputRegex, listOfFields, fieldsToRemove)

I get the same failure in both code blocks (in or out of method) - very odd. Looks like some kind of issue with accessing result.group(..) before the match iterator is materialized somehow - if you add something silly like println(result) before creating resultMap this works (!). — Tzach Zohar
– Tzach Zohar, Commented Oct 17, 2016 at 17:12
@TzachZohar yes, there's an old mailing list thread where someone noticed it working in REPL because REPL invokes toString. — som-snytt
– som-snytt, Commented Oct 17, 2016 at 18:26

som-snytt · Accepted Answer · 2016-10-17 18:24:55Z

Try 2.12? The restriction about advancing the iterator is a gotcha in the API that was finally addressed.

$ scala
Welcome to Scala 2.12.0-RC1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_101).
Type in expressions for evaluation. Or try :help.

scala> :pa
// Entering paste mode (ctrl-D to finish)

import scala.util.matching.Regex

def regexParsing(inputRecord:String, inputRegex:String, listOfFields:Seq[String], fieldsToRemove:Seq[String]): scala.collection.Map[String,Any] = {
    val logPattern = new Regex(inputRegex, listOfFields:_*)
    val result = logPattern.findAllIn(inputRecord)
    val resultMap = result.groupNames.map(a => Map(a.toString -> result.group(a))).reduce(_++_)
    return resultMap
}

val inputRecord = """s2222f"""
val inputRegex = """(.*)"""
val listOfFields = Seq("field")
val fieldsToRemove = Seq("field1", "field2")

// working 
val logPattern = new Regex(inputRegex, listOfFields:_*)
val result = logPattern.findAllIn(inputRecord)
val resultMap = result.groupNames.map(a => Map(a.toString -> result.group(a))).reduce(_++_)

// Exiting paste mode, now interpreting.

import scala.util.matching.Regex
regexParsing: (inputRecord: String, inputRegex: String, listOfFields: Seq[String], fieldsToRemove: Seq[String])scala.collection.Map[String,Any]
inputRecord: String = s2222f
inputRegex: String = (.*)
listOfFields: Seq[String] = List(field)
fieldsToRemove: Seq[String] = List(field1, field2)
logPattern: scala.util.matching.Regex = (.*)
result: scala.util.matching.Regex.MatchIterator = non-empty iterator
resultMap: scala.collection.immutable.Map[String,String] = Map(field -> s2222f)

scala> regexParsing(inputRecord, inputRegex, listOfFields, fieldsToRemove)
res0: scala.collection.Map[String,Any] = Map(field -> s2222f)

scala> :quit

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