What is the point of the class Option[T]?

You’ll get the point of Option better if you force yourself to never, ever, use get. That’s because get is the equivalent of “ok, send me back to null-land”.

So, take that example of yours. How would you call display without using get? Here are some alternatives:

getPerson2 foreach (_.display)
for (person <- getPerson2) person.display
getPerson2 match {
  case Some(person) => person.display
  case _ =>
}
getPerson2.getOrElse(Person("Unknown", 0)).display

None of this alternatives will let you call display on something that does not exist.

As for why get exists, Scala doesn’t tell you how your code should be written. It may gently prod you, but if you want to fall back to no safety net, it’s your choice.

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You nailed it here:

is the only advantage of Option[T] is
that it explicitly tells the
programmer that this method could
return None?

Except for the “only”. But let me restate that in another way: the main advantage of Option[T] over T is type safety. It ensures you won’t be sending a T method to an object that may not exist, as the compiler won’t let you.

You said you have to test for nullability in both cases, but if you forget — or don’t know — you have to check for null, will the compiler tell you? Or will your users?

Of course, because of its interoperability with Java, Scala allows nulls just as Java does. So if you use Java libraries, if you use badly written Scala libraries, or if you use badly written personal Scala libraries, you’ll still have to deal with null pointers.

Other two important advantages of Option I can think of are:

• Documentation: a method type signature will tell you whether an object is always returned or not.

• Monadic composability.

The latter one takes much longer to fully appreciate, and it’s not well suited to simple examples, as it only shows its strength on complex code. So, I’ll give an example below, but I’m well aware it will hardly mean anything except for the people who get it already.

for {
  person <- getUsers
  email <- person.getEmail // Assuming getEmail returns Option[String]
} yield (person, email)