var s: Int = 0

def function(s: Int): Boolean={

   s += 1

   return true

}

implicit class MutableInt(var value: Int) {
  def inc() = { value+=1 }
}

def function(s: MutableInt): Boolean={
   s.inc() // parentheses here to denote that method has side effects
   return true
}

scala> val x: MutableInt = 0
x: MutableInt = MutableInt@44e70ff

scala> function(x)
res0: Boolean = true

scala> x.value
res1: Int = 1

val number: Int = numberStream.next

var s: Int = 0

def function(s: Int): Boolean={

   var newS = s
   newS = newS + 1
   s = newS
   return true

}