CODEWITHSUNDEEP
scala
blue-sky
blue-sky

Reputation: 53876

Generating a random String using functional principles

Below is code I wrote to generate a random String (to be used for filename) : 

import scala.collection.mutable.ListBuffer

object FileName{

  var currentFileNameList: ListBuffer[String] = new ListBuffer

  def getFileName(): String = {
    var fileName = java.util.UUID.randomUUID().toString();

    while (true) {
      if (!currentFileNameList.contains(fileName)) {
        currentFileNameList = currentFileNameList :+ fileName
        return fileName
      } else {
        fileName = java.util.UUID.randomUUID().toString();
      }
    }

    throw new RuntimeException("Error - filename not generated")
  }

}

The exception throw new RuntimeException("Error - filename not generated") should never be thrown but is required as I need to return type String. What is Scala compiler not complaining that im throwing a RuntimeException instead of returning String ?

Is there functional equivalent (no vars) of re-writing above code ?

Upvotes: 0

Views: 299

Answers (1)

Peter Neyens
Peter Neyens

Reputation: 9820

The result type of throwing an exception in Scala is Nothing which is the bottom type and thus can be used where (in your case) a String is expected.

The chance of UUID collisions is very small (see this question and wikipedia), but if you really want to check for file name collisions in a more functional matter, you could use a tail recursive function.

def randomFileName(existing: List[String]) : String = {
  val uuid = java.util.UUID.randomUUID.toString
  if (existing.contains(uuid)) randomFileName(existing)
  else uuid
}

Upvotes: 2

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