I'm having trouble to implement the following requirement in a functional way in scala. Given a predefined number of boolean flags, I want to build up a collection of numbers. For each (true) flag, a hardcoded number should be included in the collection.

This is the unsatifying solution I have so far:

  def createCodeArray(flagA:Boolean, flagB:Boolean, flagC:Boolean): Seq[Int] = {
    val codes = ListBuffer.empty[Int]

    if(flagA) codes += 2
    if(flagB) codes += 7
    if(flagC) codes += 12

    return codes

I'm trying to achieve to same with pattern matching, but I don't want to list all the possible combinations. Also, I'd like to avoid mutable data-structures.

Any suggestion on how to write this in a functional way is much appreciated

  • 1
    \$\begingroup\$ Could you tell us more about where these flags come from, how this method is called, and how the resulting list will be used? \$\endgroup\$ – 200_success May 19 '17 at 12:49
  • \$\begingroup\$ @200_success this should not matter for this question, the method's functionality and signature should just remain as it is \$\endgroup\$ – Raphael Roth May 19 '17 at 18:43

You could use tuples to pair your flags with an Int. Throw those into a Seq and then perform a filter and then a map on that Seq. Here is how that would look:

def f(a: Boolean, b: Boolean, c: Boolean): Seq[Int] = {

 val xs = Seq((a, 2), (b, 7), (c, 12))

 xs.filter(t => t._1).map(t => t._2) 


Note that in Scala you don't need to use a return statement as long as the last bit of code in your function returns a new value.

  • \$\begingroup\$ @thanks, I'm aware that the return statement is not needed, still I'd like to use it to make the code more "speaking" \$\endgroup\$ – Raphael Roth May 19 '17 at 18:44
  • 1
    \$\begingroup\$ @Raphael, sure with return statement it is more "speaking", but it is against Scala coding style. A good explanation is given here. \$\endgroup\$ – Antot May 20 '17 at 6:16

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