CODEWITHSUNDEEP
functionscala
Core_Dumped
Core_Dumped

Reputation: 4719

passing 'val' type to a function

I was working on a code in which I declared a 'val' type variable and passed it to a recursive function which changes it:

def calculateDates(from: LocalDate, until: LocalDate, by: RDate, holidays: HolidayCalendar): Seq[LocalDate] = 
{
    val dateSeq: Seq[LocalDate] = Seq(from)
    def calculateDatesRecur(from: LocalDate, dateSeq: Seq[LocalDate]): Seq[LocalDate] =
   {
        val date = by(from, holidays)
        if (date.compareTo(until) <= 0)
          calculateDatesRecur(date, dateSeq :+ date)
        else
          dateSeq
   }
   calculateDatesRecur(from, dateSeq)
}

'dateSeq' is a variable that ultimately is a list of dates from 'from' to 'until'. Well, it turns out it works. It shouldn't right? Because the 'dateSeq' variable has been initialised as 'val'. Is it that a copy of it is sent to the recursive function?

Upvotes: 0

Views: 120

Answers (2)

Shadowlands
Shadowlands

Reputation: 15074

It isn't that a copy of dateSeq is passed into calculateDatesRecur, rather, the expression dateSeq :+ date creates a new Seq[Date] (with the newly added date, and without modifying the dateSeq parameter), which is then passed to the recursive call. In this way, a final Seq[Date] is built up from successive immutable, intermediate values, and eventually handed back when the else clause is executed.

Upvotes: 2

Ashalynd
Ashalynd

Reputation: 12573

dateSeq :+ date returns the new object. Check the definition of :+ method: http://www.scala-lang.org/api/current/index.html#scala.collection.Seq

Upvotes: 0

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