Scala example source code file (mapConserve.scala)

This example Scala source code file (mapConserve.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

anyref, array, bigint, bigint, function1, int, int, list, list, nil, test, test, x

The Scala mapConserve.scala source code

import scala.annotation.tailrec
import scala.collection.mutable.ListBuffer

object Test {
  val maxListLength = 7 // up to 16, but larger is slower
  var testCount = 0
  
  def checkStackOverflow() = {  
    var xs: List[String] = Nil
    for (i <- 0 until 250000)
        xs = "X" :: xs

    val lowers = xs.mapConserve(_.toLowerCase)
    assert(xs.mapConserve(x => x) eq xs)
  }

  def checkBehaviourUnchanged(input: List[_], oldOutput: List[_], newOutput: List[_]) {
    if (oldOutput eq input)
      assert(newOutput eq oldOutput)
    else {
      assert(newOutput.head == oldOutput.head)
      checkBehaviourUnchanged(input.tail, oldOutput.tail, newOutput.tail)
    }
    testCount += 1
  }

    var callCount = 0
    val lastHexDigit: Function1[BigInt, AnyRef] = { x: BigInt => callCount+=1; if (x < 16) x else x % 16 }

    def main(args: Array[String]) {
        for (length <- 0 to maxListLength;
             bitmap <- 0 until (1 << length);
             data = List.range(0, length) map { x: Int =>
               if ((bitmap & (1 << x)) != 0) BigInt(x+16)
               else BigInt(x)
             })
        {
            // Behaves like map with respect to  ==
            callCount = 0
            val numUnconserved = data.reverse.dropWhile(_ < 16).length
            val result = data mapConserve lastHexDigit
            val mapResult = data map lastHexDigit
            assert(result == mapResult)
            assert((result drop numUnconserved) eq (data drop numUnconserved))
            assert(callCount == 2 * length) // map, mapConserve call transform for each element in the list

            // Behaves like existing mapConserve with respect to  eq
            checkBehaviourUnchanged(data, data mapConserve lastHexDigit, data mapConserve lastHexDigit)
        }
        
        checkStackOverflow();
    }
}