Wrong forward reference with Null initialisation

Question

Quite often in Java we see algorithms like:

MyObject currentObject = null 

for(MyObject oldObject: objects){
    if(currentObject != null) doSomething
    else doSometing
    currentObject = oldObject  
}

I'm trying to implement this in Scala:

var currentObject: MyObject = null
for(oldObject <- objects){
    if(currentObject != null) doSomething
    else doSometing
    currentObject = oldObject  
}

However, I'm receiving a Wrong Forward reference compilation error.

I guess the problems is with the initialisation as null of the currentObject?

UPDATED:

Here the actual code:

var protCoord:Coordinates     = new Coordinates()
var prevprotCoord:Coordinates = new Coordinates()
var coordMap = mutable.Map[Coordinates, GenomeCoordinates]()
var protein:EnsemblProteinEntry = null
var codingLength = 0

for (gtfEntry <- gtfEntries.toStream) {
  if (gtfEntry.isGene)
    mapping.addGene(new GTFGeneEntry(gtfEntry))
  if(gtfEntry.isTranscript){
    mapping.addTranscriptID(gtfEntry)
  if(protein != null) protein.multiMapCoordinates = coordMap // **I'm receiving the error here** 
    var protein = fastaEntries.getOrElse(gtfEntry.transcriptIdentifier, null)
  if(protein == null)
    protein = new EnsemblProteinEntry()
  protCoord = new Coordinates()
  prevprotCoord = new Coordinates()
  coordMap = mutable.Map[Coordinates, GenomeCoordinates]()
  codingLength = 0
}

Thanks in advance.

Note: Try to avoid using `null` in Scala - use `Option` (with its subtypes `Some` and `None`) instead. See: http://stackoverflow.com/questions/9698391/when-to-use-option — Jesper, Aug 26 '16 at 13:21
I suspect that if you do `for{ whatever <- ... } { theVar = whatever }` it will work, but against all this encoding. — pedrofurla, Aug 26 '16 at 17:06
Btw, Scala `for`s need to have a "right hand side", or something after then, either a straight expression (or block like `{...}`) or followed by `yield` with a expression or block. — pedrofurla, Aug 26 '16 at 17:08

score 2 · Accepted Answer · answered Aug 26 '16 at 14:23

2

Inside the loop you have var protein defined second time. The problem is that you try to use protein inside loop before it's defined.

answered Aug 26 '16 at 14:23

Nebril

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Wrong forward reference with Null initialisation

1 Answers1