Is there a way to handle the last case differently in a Scala for loop?

Question

For example suppose I have

  for (line <- myData) {
    println("}, {")
  }

Is there a way to get the last line to print

println("}")

Answer 1

Can you refactor your code to take advantage of built-in mkString?

scala> List(1, 2, 3).mkString("{", "}, {", "}")
res1: String = {1}, {2}, {3}

Answer 2

Before going any further, I'd recommend you avoid println in a for-comprehension. It can sometimes be useful for tracking down a bug that occurs in the middle of a collection, but otherwise leads to code that's harder to refactor and test.

More generally, life usually becomes easier if you can restrict where any sort of side-effect occurs. So instead of:

for (line <- myData) {
  println("}, {")
}

You can write:

val lines = for (line <- myData) yield "}, {"
println(lines mkString "\n")

I'm also going to take a guess here that you wanted the content of each line in the output!

val lines = for (line <- myData) yield (line + "}, {")
println(lines mkString "\n")

Though you'd be better off still if you just used mkString directly - that's what it's for!

val lines = myData.mkString("{", "\n}, {", "}")
println(lines)

Note how we're first producing a String, then printing it in a single operation. This approach can easily be split into separate methods and used to implement toString on your class, or to inspect the generated String in tests.