Converting object oriented style code to functional in Scala

I came across Java like Scala code that I am trying to refactor to make it functional and immutable. The first obvious flaw is that it's violating thread safety by using mutable public class level collections.

Those methods (insText, insInt, etc) look unnecessary and can be removed with higher order function (where function takes in dd => Int, dd => String type of thing). Class DDType is wrong with all mutable variables. Should I change class level mutable sets to private immutable sets?

Do you agree with those changes and overall refactoring approach?

class SaveObject extends Update with QueryFormatter {

  val keys    = mutable.Set[(DomainDictionary, Int   )]()
  val inserts = mutable.Set[(DomainDictionary, String)]()

  implicit def toInt(value:String) = value.toInt
  implicit def toDouble(value:String) = augmentString( value ).toDouble
  implicit def toBool(value:String) = value.toBoolean
  implicit def toTs(value:String) = {
  val date:Date = dateFormat.parse(value)
    new Timestamp(date.getTime)
}
implicit def toDate(value:String):Date = {
  dateFormat.parse(value)
}

def add(dd:DomainDictionary, value:String) = {
// check if its a key
getType(dd) match {
  case x if x.isKey    => id(dd, value)
  case x if x.isText   => insText(dd, value)
  case x if x.isInt    => insInt(dd, value)
  case x if x.isDouble => insDouble(dd, value)
  case x if x.isBool   => insBool(dd, value)
  case x if x.isTs     => insTs(dd, value)
  case x if x.isDate   => insDate(dd, toDate(value))
  case _               =>
    val msg = "Could not convert type for dd %s and value %s".format(dd.id, value)
    throw new Exception(msg)
 }
}
class DDType(dd:DomainDictionary) {
var isKey    = false
     var isText   = false
     var isInt    = false
     var isDouble = false
     var isBool   = false
     var isTs     = false
     var isDate   = false
 }
 def getType(dd:DomainDictionary):DDType = {
   val theType = new DDType(dd)
   val ns = dd.namespace
   val isKey = namespaceMatcher(ns,
   (ns,table,key)=>false.toString,
   (ns,table,key)=>false.toString,
   (ns,table,key)=>if(key == QueryPathfinder.ID) true.toString else false.toString
)


 if(toBool(isKey)){
   theType.isKey = true
 }
 else {
   val ddType = dd.domainDictionaryType
   ddType match {
     case "text" => theType.isText = true
     case "numeric" => theType.isInt = true
     case "alphanumeric" => theType.isText = true
     case "date" => theType.isDate = true
     case "timestamp" => theType.isTs = true
     case "boolean" => theType.isBool = true
     case "currency" => theType.isInt = true
     case _ => {} //this is wrong
   }
 }



theType
}
def id(dd:DomainDictionary, key:Int){
  keys += Tuple2(dd, key)
}
def insText(dd:DomainDictionary, value:String) = {
  inserts += Tuple2(dd,value)
}
def insInt(dd:DomainDictionary, value:Int) = {
    inserts += Tuple2(dd,value.toString)
}
def insDouble(dd:DomainDictionary, value:Double) = {
  inserts += Tuple2(dd,value.toString)
}
def insTs(dd:DomainDictionary, value:Timestamp) = {
  val date = new Date(value.getTime)
  inserts += Tuple2(dd,dateFormat.format(date))
 }
 def insDate(dd:DomainDictionary, value:Date) = {
    inserts += Tuple2(dd,dateFormat.format(value))
 }
  def insBool(dd:DomainDictionary, value:Boolean) = {
    inserts += Tuple2(dd,value.toString)
  }

}