A post about nothing in Scala

The post at the following URL explains nothingness in Scala.

https://oldfashionedsoftware.com/2008/08/20/a-post-about-nothing/

From the URL:

"The method getAStringMaybe returns Option[String]. Option is an abstract class with exactly two subclasses, class Some and object None. Those are the only two ways to instantiate an Option. So getAStringMaybe returns either a Some[String] or None. Some and None are case classes, so you can use the handy match/case construct to handle the result. None is object that signifies no result from the method.

The purpose of an Option[T] return type is to tell callers that the method might return a T in the form of a Some[T], or it might return None to signify no result. This way, the caller supposedly knows when he does and does not need to check for a good return value."

Unit is the same as void in Java

"This is another easy one. Unit is the type of a method that doesn’t return a value of any sort. Sound familiar? It’s like a void return type in Java. Here’s an example:

scala> def doThreeTimes(fn: (Int) => Unit) = {
| fn(1); fn(2); fn(3);
| }
doThreeTimes: ((Int) => Unit)Unit"

"One other use of Nothing is as a return type for methods that never return. It makes sense if you think about it. If a method’s return type is Nothing, and there exists absolutely no instance of Nothing, then such a method must never return.

Your logging method would return Unit. There is a value Unit so it can actually be returned. From the API docs:

Unit is a subtype of scala.AnyVal. There is only one value of type Unit, (), and it is not represented by any object in the underlying runtime system. A method with return type Unit is analogous to a Java method which is declared void."

http://stackoverflow.com/questions/26563213/how-to-instantiate-unit-in-scala

You can just use () whose type is Unit:

scala> import scala.collection.mutable.HashMap
import scala.collection.mutable.HashMap

scala> val myMap = new HashMap[String, Unit]()
myMap: scala.collection.mutable.HashMap[String,Unit] = Map()

scala> myMap + ("myStringKey" -> ())
res1: scala.collection.mutable.Map[String,Unit] = Map(myStringKey -> ())

This is a comment taken from Unit.scala:

There is only one value of type Unit, (), and it is not represented by any object in the underlying runtime system.