Options and Exceptions in Scala

Option is solution to a Billion Dollar Mistake introduced by Null Pointer Exceptions. Options deal with unsafe APIs and never do null checks.
As .get is a unsafe operation, we should rely on map/flatMap to read the values from options.
Since we can use map, flatMap on options, we can also use for comprehension.

Scala Implementation Classes

        sealed abstract class Option[+A]
        case class Some[+A](x: A) extends Option[A]
        case object None extends Option[Nothing]

Code Sample

     val config: Map[String, String] = Map(
             "age" -> "36",
             "gender" -> "Male"
         )

         class Person {
             def getPerson = println("person created")
         }
         object Person {
             val random = new Random(System.nanoTime())

             def apply(age: String, gender: String): Option[Person] =
                 if(random.nextBoolean()) Some(new Person)
                 else None
         }

         // by default .get on map returns option
         val age = config.get("age")
         val gender = config.get("gender")
         // NOTE: age.get is unsafe operation and hence we should only rely on map/flatMap to get the value from options
         /*
             if (age != null && gender != null)
                 return Person(age, gender)
             else
                 return null
          */
         val person = age.flatMap(a => gender.flatMap(g => Person(a, g)))
         /*
             if (person != null)
                 return person.getPerson
             else
                 return null
          */
         val personStatus = person.map(c => c.getPerson)
         /*
             Same as
             if (status != null)
                 println(status)
          */
         personStatus.foreach(println)

         // shorthand chained solution
         config.get("age")
           .flatMap(h => config.get("gender")
             .flatMap(p => Person(h, p))
             .map(c => c.connect))
           .foreach(println)

         // for comprehensions: Instead of using chained or multiple map/flatmaps we can use this for readability (much widely used and more readable)
         // If any of the the for statements in None, then entire for-yield will return None
         val forPersonStatus = for {
             age <- config.get("age")
             gender <- config.get("gender")
             Person <- Person(age, gender)
         } yield Person.connect

         forPersonStatus.foreach(println)

Exceptions
In imperative languages like Java, as number of try blocks increases, program becomes barely readable
Scala provides a way to avoid countless try-catch blocks

Scala Implementation Classes

        sealed abstract class Try[+T]
        case class Failure[+T](t: Throwable) extends Try[T]
        case class Success[+T](value: T) extends Try[T]

Code Sample

     val aSuccess = Success(3)
         val aFailure = Failure(new RuntimeException("Not valid"))
         println(aSuccess)
         println(aFailure)

         // unsafe methods
         def unsafeMethod = throw new RuntimeException("Unsafe method invoked")
         // Try with apply method is going to catch the exception and wrap it in Failure object
         val potentialFailure = Try(unsafeMethod)
         println(potentialFailure)
         println(potentialFailure.isSuccess) // tells whether exception is thrown or not

         // orElse
         def backUpMethod(): String = "A valid result"
         val fallbackTry = Try(unsafeMethod).orElse(Try(backUpMethod))
         println(fallbackTry)

         // design the apis in better way
         def betterUnsafeMethod: Try[String] = Failure(new RuntimeException("Better Unsafe method"))
         def betterBackupMethod: Try[String] = Success("Better valid result")
         val betterFallback = betterUnsafeMethod orElse betterBackupMethod
         println(betterFallback)

         // map, flatMap, filter
         println(aSuccess.map(_ * 3))
         println(aSuccess.flatMap(x => Success(x * 10)))
         println(aSuccess.filter(_ > 10)) // this will turn success into failure

         // since map, flatMap, filter are available so will be for-comprehension