scala code functional-programming facelift: extracting String from List[List[myClass.toString]] structure

Question

Please show me how to rewrite toString in a functional way.

The code is ok, but nothing to be proud of, there are 3 temporary variables in it.

class Field(x: Int, y: Int) {
  val value = init(x,y)
  private def init(x: Int, y: Int) = List.fill(x,y)(new Cell)
  override def toString(): String = {
    val temp = new StringBuilder
    for(i <- value) {
      for(j <- i) {
        temp.append(j.toString())
      }
      temp.append("\n")
    }
    temp.mkString
  }
}

Thanks guys!

Tomasz Nurkiewicz · Accepted Answer · 2012-06-27 20:22:57Z

5

What about this (look ma! one line):

override def toString() = value.map(_.mkString).mkString("\n")

Sometimes it frightens me how compact Scala code can be...

BTW if you don't need to reuse init() method you can simply say:

val value = List.fill(x,y)(new Cell)

answered Jun 27, 2012 at 20:22

Tomasz Nurkiewicz

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5 Comments

Rex Kerr Over a year ago

Just what I was about to post. Might not be as fast as the original, but it's way shorter and clearer.

Lorinc Nyitrai Over a year ago

Tomasz, yes, I used exactly your one-liner, but I could not rewrite it to handle the fact that the value that I need to concatenate is retrieved by calling the Cell.toString()

Tomasz Nurkiewicz Over a year ago

@NyitraiLőrinc: List.mkString implicitly calls toString of each element, can you show more code as it works fine for me with custom Cell class

Lorinc Nyitrai Over a year ago

omg, it works. now I will spend a few hours to understand exactly why. thanks :)

Lorinc Nyitrai Over a year ago

I was mislead by writing the Cell.toString after I tossed away the original one liner. I'm new to Scala (and probably to development), but this elegance is simply brilliant. Thx again.

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