How to pass a scala class as an object into a function parameter?

Question

How do I run the refint1 function? I've triedvar x = new RefInt(5) and then doing scala> argpass.refint1(x)but get a found: RefInt, required : argpass.RefInt => Unit error in the console.

object argpass{
       class RefInt (initial : Int) {
         private var n : Int = initial
         def get () : Int = n
         def set (m : Int) : Unit = { n = m}
        }
        def refint1 ( f: RefInt => Unit) : (Int, Int, Int) = {
          var x = new RefInt(5)
          val first = f(x)
          val firstget = x.get
          val sec = f(x)
          val secget = x.get
          val third = f(x)
          val thirdget = x.get
          (firstget, secget, thirdget)
    }

//How do i run the refint1 function?

First f is a function from RefInt to Unit (equivalent of Java's void). Thus, you need to pass a function, not a value. - Second, since the function returns an Unit, storing its result _(in first, second & third) is meaningless. - Third, x, even if muted internally by f, is not reassigned, thus it may (should IMHO) be a val. - Finally you can call refint1 like this: refint1 { ri => ri.set(i); i += 1 } where var i = 0. — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Mar 1, 2019 at 3:02

Rodrigo Vedovato · Accepted Answer · 2019-03-01 15:06:43Z

2

As Luis said in the comments, f returns Unit, which is basically void. This should solve your problem:

class RefInt(initial: Int) {
  var n: Int = initial
  def get(): Int = n
  def set(m: Int): Unit = { n = m }
}

def refint1(f: RefInt => Unit): (Int, Int, Int) = {
  var x = new RefInt(5)  
  f(x)
  val firstget = x.get
  f(x)
  val secget = x.get
  f(x)
  val thirdget = x.get

  (firstget, secget, thirdget)
}

That being said, I think you can improve your design a little bit. Here's a different approach to solve the same problem:

case class RefInt(initial: Int)

def refInt1(initial: RefInt, f: RefInt => RefInt) : (Int, Int, Int) = {  
  val x0 = f(initial)
  val x1 = f(x0)
  val x2 = f(x1)

  (x0.initial, x1.initial, x2.initial)
}

println(refInt1(RefInt(5), ri => ri.copy(ri.initial * 2)))

edited Mar 1, 2019 at 15:06

answered Mar 1, 2019 at 14:26

Rodrigo Vedovato

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