Null and Nothing

Null and Nothing are called Bottom types in Scala. Why do we need these Bottom types? Take a look at the code snippet:

def checkIF10AndReturn20(x: Int): Int =  {
  if(x == 10)
    x * 2
  else 
    throw new Exception("Sorry, Value wasn't 10")
 }

The method checkIf10AndReturn20 expects a returned value of Int type, but what's happening here is different. If the passed argument value is not 10, we are throwing an exception, yet still the compiler is OK with our code. How can this be possible?

This is because of Type Inference. It always looks for common types in both branches of an if statement, so if in the other branch, the type extends everything, then the inferred type will automatically be the first one. In Scala, Nothing is a subtype of everything, hence the inferred type automatically becomes of type Int. Let's visualize this:

With this, it's important to understand that Type Inference plays an important role in Scala's ecosystem.