Translate boolean flags to collection of numbers in scala

Question

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

• 200_success: Could you tell us more about where these flags come from, how this method is called, and how the resulting list will be used?
• Raphael Roth: @200_success this should not matter for this question, the method's functionality and signature should just remain as it is

Answer 1

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.

• Raphael Roth: @thanks, I'm aware that the return statement is not needed, still I'd like to use it to make the code more "speaking"
• Antot: @Raphael, sure with return statement it is more "speaking", but it is against Scala coding style. A good explanation is given here.