safer_ints.scala

object typesWrapped {

  case class Divided( value: Int ) extends AnyVal
  case class Subtracted( value: Int ) extends AnyVal
  case class Multiplied( value: Int ) extends AnyVal

  def divide( i: Int ): Divided = Divided( ( i / 5 ).toInt )

  def subtract( i: Divided ): Subtracted = Subtracted( i.value - 10 )

  def multiply( i: Subtracted ): Multiplied = Multiplied( i.value * -1 )

  def allOK( i: Int ): Int = {
    val s1 = divide( i )
    val s2 = subtract( s1 )
    val s3 = multiply( s2 )
    s3.value
  }

  def allBAD( i: Int ): Int = {
    val s1 = divide( i )
    val s2 = multiply( s1 ) // this one doesn't compile
    val s3 = subtract( s2 )
    s3.value
  }

}

/*
scala> :load typesWrapped.scala
Loading typesWrapped.scala...
<console>:28: error: type mismatch;
 found   : typesWrapped.Divided
 required: typesWrapped.Subtracted
           val s2 = multiply( s1 )
                              ^

*/