Scala is not looping through the for loop

Question

I have an assignment where I need to develop N in a row in Scala. For the representation of the board I want to loop through the 2d Array and print the X' en O's. This is the code for that:

  override def toString(): String = {
    val repres = ""

    for (rowIndex <- 0 until board.length - 1) {
      for (columnIndex <- 0 until board(rowIndex).length - 1) {
        if (board(rowIndex)(columnIndex) == Player.Player1) {
          repres + "X"
        } else if (board(rowIndex)(columnIndex) == Player.Player2) {
          repres + "O"
        } else if (board(rowIndex)(columnIndex) == Player.NoPlayer) {
          repres + "_"
        } else {
          throw new IllegalArgumentException
        }
      }
      repres + Properties.lineSeparator
    }
    repres
  }

This is the board:

var board = Array.fill[Player](rows,columns) {Player.NoPlayer}

For some reason it is not going through the for loop even though board.length is 6 in debugging.

I am new to scala so there is probably something very obvious wrong that I am just not seeing.

Thanks for the help

jbx · Accepted Answer · 2019-03-19 14:38:45Z

3

I think the problem is not the loop. Are you expecting repres to change?

You have declared repres as an immutable String. All the operations you are doing are pretty much futile, it is creating a new String in each branch but you are not assigning it to anything. The last statement returns repres as an empty String.

Try to change the declaration to var repres.

Then each of the branches needs to change to repres = repres + "X" etc.

Note that this is not really functional. It's just Java adapted to Scala syntax.

answered Mar 19, 2019 at 14:38

jbx

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1 Comment

kjwdamme Over a year ago

Ahh thank you. Ofcourse. Completely forgot about that. I was doing repres = repres + "X" before but it gave an error. Didn't realize that was because I was using a val instead of var. I know it is not functional. Point of the assignment is to first do it this way and changing it to functional later

Dima · Accepted Answer · 2019-03-19 15:46:52Z

2

You should not be using mutable variables. They make code less readable, and harder to reason about, and may create many hard to debug problems potentially.

In 95% uses cases in scala, you don't need mutable state, so my recommendation is that you just pretend it does not exist at all until you get enough grasp of the language to be able to definitively distinguish the other 5% of the cases.

 val repres = board.flatten.map { 
   case Player.Player1 => "X"
   case Player.Player2 => "O"
   case _ => "_"
 }.mkString
  .grouped(board.length)
  .mkString(Properties.lineSeparator)

answered Mar 19, 2019 at 15:46

Dima

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