ADT basics

quantity.sc

sealed trait Quantity

object Quantity {
  final case class UnitQuantity private (units: Int) extends Quantity
  final case class WeightQuantity private (kgs: Double) extends Quantity  
  
  // factory with validation
  object UnitQuantity {
    def create(units: Int): Either<ValidationError, UnitQuantity> =
      if (units <= 0) Either.left(ValidationError("units must be positive")) 
      else Either.right(UnitQuantity(units))
  }
  
  // factory with validation
  object WeightQuantity {
    def create(units: Int): Either<ValidationError, WeightQuantity> =
      if (units <= 0.0) Either.left(ValidationError("kgs must be positive")) 
      else Either.right(UnitQuantity(units))
  }
  
}