One aspect that the author mentions only in passing–but is interesting to look at in more detail–is to understand how Scala has solved this in a very consistent

One aspect that the author mentions only in passing–but is interesting to look at in more detail–is to understand how Scala has solved this in a very consistent and satisfying fashion: Instead of mixing "you can't override this in a subclass" and "you can't reassign this value" as Java did with final, it clearly separates these concerns: class Foo { var qux = 1.23 val bar = 42 final var fiz = "fiz" final val wow = "wow" } (new Foo).qux = 2.34 // valid (new Foo).bar = 23 // invalid (new Foo).fiz = "fuz" // valid (new Foo).wow = "wew" // invalid class SubFoo extends Foo { override var qux = 2.34 // valid override val bar = 23 // valid override var fiz = "fuz" // invalid override val wow = "wew" // invalid }