Scala Programming Projects

Refactoring nbOfMonthsSavings

In the previous section, we changed the return type of nbOfMonthsSavings to return Option[Int]. The function returned None if the expenses arguments were greater than income. We are now going to change it to return an error message wrapped in Left.

We could use a simple string for our error message, but the best practice when using Either is to create an ADT for all of the possible error messages. Create a new Scala class in src/main/scala/retcalc called RetCalcError, as shown in the following code:

package retcalcsealed abstract class RetCalcError(val message: String)object RetCalcError {  case class MoreExpensesThanIncome(income: Double, expenses: Double)   extends RetCalcError( s"Expenses: $expenses >= $income. ...