overloading constructor based on condition in scala

Question

i've a simpleNode class with two inputs that u can only fill one of them which are both Map in Scala but i have to check to the type of data in maps in order to fill any of the inputs

the code i've written to do so is:

class SimpleNode (
  val uriTriples: collection.mutable.Map[String, List[String]] = collection.mutable.Map.empty,
  val valueTriples: collection.mutable.Map[String, Map[String,String]] = collection.mutable.Map.empty
                ) 
  {              
    def this(map:collection.mutable.Map) = {
      map.values.head match {
      case uri : List[String] => this(uris,null) 
      case values : Map[String,String] => this(null,values)
      case _=>
    }
  }
}

I always face the error :

a:34: error: 'this' expected but identifier found.
[INFO]        map.values.head match {
[INFO]        ^

http://stackoverflow.com/questions/1095329/scala-constructor-overload — Brian, Aug 20 '13 at 18:08
@Brian , it's what i tried , but no examples seen with switch case so i faced that error — Hady Elsahar, Aug 20 '13 at 18:13

score 3 · Answer 1 · answered Aug 20 '13 at 18:24

3

Usual strategy for disambiguation:

class SimpleNode (
  val uriTriples: collection.mutable.Map[String, List[String]] = collection.mutable.Map.empty,
  val valueTriples: collection.mutable.Map[String, Map[String,String]] = collection.mutable.Map.empty
)
  {
    def this(map:mutable.Map[String, List[String]]) = this(map, null)
    def this(map:mutable.Map[String, Map[String,String]])(implicit d: DummyImplicit) = this(null, map)
}

Or a factory is more pedestrian:

object SimpleNode {
  def apply(...) = ???
}

answered Aug 20 '13 at 18:24

som-snytt

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isn't the dummyimplicit dupricated in scala ? – Hady Elsahar Aug 20 '13 at 18:47
@HadyElsahar Not to my limited knowledge. http://www.scala-lang.org/api/current/index.html#scala.Predef$$DummyImplicit – som-snytt Aug 21 '13 at 04:31
@HadyElsahar I thought you meant deprecated. – som-snytt Aug 25 '13 at 15:02

overloading constructor based on condition in scala

1 Answers1