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implicit class

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In Python you take every n-th character of a string like this:

>>> s = 'hello python and scala'
>>> s[::2]
'hlopto n cl'

In Scala you can't do it that easily (or at least I haven't found it yet). I asked this question on IRC at #scala and we came up with this solution:

scala> val s = "hello python and scala"
scala> (for (i <- 0 until s.length if i % 2 == 0) yield s(i)).mkString
res16: String = hlopto n cl

Make it an implicit class

Using implicit classes, Scala allows you to add new operations to existing classes, no matter whether they come from Scala or Java!

Jacoby6000 suggested to make it an auxiliary method for strings. In Scala you can do it with an implicit class. Here is a complete solution:

#!/usr/bin/env scala

import scala.math

object Implicits
{
  implicit class PimpedString(str: String)    // we want to extend the String class with our method
  {
    def everyNthChar(skipNum: Int): String = {
      (for (i <- str.indices if i % skipNum == 0) yield str(i)).mkString
    }
    // other methods I want strings to have go here
  }

  implicit class PimpedInt(x: Int) {
    def pow(y: Int): Int = {
      math.pow(x, y).toInt
    }
    // other methods I want ints to have go here
  }

}


object Main extends App 
{
  import Implicits._

  // Lookie here! Our method looks like a normal string method:
  println("Hey Look, I can use methods from PimpedString!".everyNthChar(3))
}

Main.main(args)

"I usually have an object that contains all of my implicits called "Implicits" eg: object Implicits { // All implicit classes here }. Then when I want to use my implicit classes I just do an import Implicits._ at the top of the class I want to have the implicits in."

Yet another example

object Implicits
{

  implicit class PimpedString(s: String) {
    def center(n: Int): String = {
      "%s%s".format(" " * ((n - s.length) / 2), s)
    }
  }

}

object Main {

  import Implicits._

  def main(args: Array[String]) {
    // center the given string using a fixed width (actually, the whitespaces are removed on the right side)
    println("*".center(9))      // "    *    "
    println("***".center(9))    // "   ***   "
  }

}