Can extractors be customized with parameters in the body of a case statement (or anywhere else that an extractor would be used)?

Question

Basically, I would like to be able to build a custom extractor without having to store it in a variable prior to using it.

This isn\'t a real example of how I would

Answer 1

Though what you are asking isn't directly possible,
it is possible to create an extractor returning a contaner
that gets evaluated value in the if-part of the case evaluation. In the if part it
is possible to provide parameters.

object DateExtractor {
  def unapply(in: String): Option[DateExtractor] = Some(new DateExtractor(in));
}

class DateExtractor(input:String){
  var value:LocalDate=null;
  def apply():LocalDate = value;
  def apply(format: String):Boolean={
    val formater=DateTimeFormatter.ofPattern(format);
    try{
      val parsed=formater.parse(input, TemporalQueries.localDate());
      value=parsed
      true;
    } catch {
      case e:Throwable=>{
        false
      }
    }
  }
}

Usage:

object DateExtractorUsage{
  def main(args: Array[String]): Unit = {
    "2009-12-31" match {
      case DateExtractor(ext) if(ext("dd-MM-yyyy"))=>{
        println("Found dd-MM-yyyy date:"+ext())
      }
      case DateExtractor(ext) if(ext("yyyy-MM-dd"))=>{
        println("Found yyyy-MM-dd date:"+ext())
      }
      case _=>{
        println("Unable to parse date")
      }
    }
  }
}

This pattern preserves the PartialFunction nature of the piece of code.
I find this useful since I am quite a fan of the collect/collectFirst methods, which take a partial function as a parameter and typically does not leave room for precreating a set of extractors.