Decreasing for loop in Scala?

scala>def decrement(start: Int, finish: Int) = {
    |  for (i <- start to finish by -1)
    |   println("Current value (decreasing from "+start+" to "+finish+") is "+i);
    | }
decrement: (start: Int,finish: Int)Unit

scala> decrement(10, 1)
Current value (decreasing from 10 to 1) is 10
Current value (decreasing from 10 to 1) is 9
Current value (decreasing from 10 to 1) is 8
Current value (decreasing from 10 to 1) is 7
Current value (decreasing from 10 to 1) is 6
Current value (decreasing from 10 to 1) is 5
Current value (decreasing from 10 to 1) is 4
Current value (decreasing from 10 to 1) is 3
Current value (decreasing from 10 to 1) is 2
Current value (decreasing from 10 to 1) is 1

for (i <- (6 to 3 by -1)) {println ("i: " + i)}
i: 6
i: 5
i: 4
i: 3

If you happen to forget by -1, you can move up and use a function, to revert the result:

for (i <- (3 to 6)) {println ("i: " + ((6+3) - i))}

To exclude the second boundary, use until:

for (i <- (6 until 3 by -1)) {println ("i: " + i)}
i: 6
i: 5
i: 4

Alternatively, you could define an Iterator for your purpose. Extending an Iterator is easy; just implement 'hasNext:Boolean' and 'Next:[T]', where T is the type to handle - in our case Int or maybe Long or BigInt:

class FromToIterator (start: Int, stop: Int) extends Iterator [Int] { 
  var current = start
  //                        3       6       3         6         6       3       6         3
  def hasNext : Boolean = ((start < stop && current <= stop) || (start > stop && current >= stop)) 
  def next: Int = { 
    val res = current
    if (start < stop) current += 1 else current -= 1
    res
  } 
}
val it = new FromToIterator (3, 6)
val ti = new FromToIterator (6, 3)

for (i <-it) println (i)
for (i <-ti) println (i)

highnum to lownum by -1 (switch with other negative or positive step to change stepping)

def decrement(start: Int, finish: Int) = {
  for (i <- start to finish by -1) {
     println("Current value (decreasing from "+start+" to "+finish+") is "+i)
  }
}

I think this is a dupe of Scala downwards or decreasing for loop?

This way you can use Decreasing for loop in Scala.

    object Example extends App {


      for(i <- 20 to 2 by -2){


        println("Value of i = "+ i)

      }
    }
------------------
O/P
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Value of i = 20
Value of i = 18
Value of i = 16
Value of i = 14
Value of i = 12
Value of i = 10
Value of i = 8
Value of i = 6
Value of i = 4
Value of i = 2