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scalaoptionparserscopt

How to pattern match on Scala Scopt optional arguments

I have a simple Scops parser that looks like

val parser: scopt.OptionParser[Config] = new scopt.OptionParser[Config]("my-app") {
  head("scopt", "3.x")
  (...)

  opt[String]('q', "query")
    .text("The query.")
    .action { (value, conf) => conf.copy(
      query = value
    )}
    .optional
}
(...)
parser.parse(args, Config()) match {
  case Some(config) => drive(config)
(...)

In my driver function I want to initialize a parameter with what the user provided via the argument or some default value otherwise.

I could do something like 

var myQuery = _
if config.query != "" myQuery = config.query
else myQuery = config.query

But, (i) I doubt that testing against the empty string is the right way to check if the user provided an optional argument or not and (ii) that doesn't look like a very functional to write this in Scala.

Question: Is there a nice functional way to do this? I considered pattern matching like below but the Scopt arguments do not seem to be returned as Option[String]

val myQuery: String = config.query match {
  case Some(q) => q
  case None => "This is the default query"
}
Solution

  • Just make Config#query an Option[String] (with None as default) and change the query = value line to query = Some(value).