Iterating while constructing immutable object in Scala

Question

I have a library class which I can't change:

class MultiPart {
  private val _parts: Seq[Part] = Seq.empty[Part])

  def addHead(head: Head): MultiPart = Multipart(_parts :+ head)

  def addPart(part: Part): MultiPart = Multipart(_parts :+ part)
}

In my code, I want to construct an immutable object of class Multipart, while iterating in a for loop. But I am not able to figure out how to do that. My current code looks like :

var mp: MultiPart = new MultiPart().addHead(head)
arrParts.foreach(x => mp.addPart(x))

Is there a way to fix this?

If you want it immutable, why don't you just create a new MultiPart with new Seq[Part]? — mfirry
– mfirry, Commented Apr 1, 2016 at 18:58

pgoggijr · Accepted Answer · 2016-04-01 17:01:10Z

1

Looks like you should use foldLeft or foldRight (similar functions in other languages are usually called reduce)

arrParts.foldLeft(new MultiPart().addHead(head))(
    (list, part) => {
        list.addPart(part)
    }
)

There's some good examples on this page if you're confused: http://oldfashionedsoftware.com/2009/07/30/lots-and-lots-of-foldleft-examples/

answered Apr 1, 2016 at 17:01

pgoggijr

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