Constructor-local variables in Scala

Question

I'm on exercise 5.7 of "Scala for the Impatient", where i need to create a class Person that takes a name:String on constructor and has 2 properties firstName and lastName filled from name split by whitespace. My first trial was :

class Person(name:String) {
  private val nameParts = name.split(" ")

  val firstName = nameParts(0)
  val lastName = nameParts(1)
}

The problem is, that now nameParts remains as a private field always visible within the class, when in fact should only exist within the constructor's local environment. The Java equivalent of what I want would be:

 class Person{
    private final String firstName;
    private final String lastName;

    Person(String name){
        final String[] nameParts = name.split(" ");
        firstName = nameParts[0];
        lastName = nameParts[1];
    }
 }

Here, nameParts exists only withing the constructor, which is what i'm aiming for. Any hints on how this can be done in Scala?

NOTE: I ended up finding a more "Scalesque" way:

class Person(name:String) {
    val firstName::lastName::_ = name.split(" ").toList 
}

but I still would like to get an answer to my question.

Answer 1

There is a way to avoid the private val. Just use the extractor of Array:

class Person(name: String) {
  val Array(first, last) = name.split(" ")
}

edit:

What you want to do can be achieved through a factory method on the companion and a default constructor that takes first and last as param:

class Person(val first: String, val last: String)

object Person {
  def apply(name: String) = {
    val splitted = name.split(" ")
    new Person(splitted(0), splitted(1))
  }
}

scala> Person("Foo Bar")
res6: Person = Person@37e79b10

scala> res6.first 
res7: String = Foo

scala> res6.last
res8: String = Bar

But for this simple case I would prefer my first suggestion.

The example in your link would also work, but it's kind of the same as my first example. Afaik there is no way to create a temporary variable in the constructor.

Answer 2

What I had in mind was simply

class Person(n: String) {
  val firstName = n.split(" ")(0)
  val lastName = n.split(" ")(1)
}

If you want to factor out the common code, then drexin's answer with the array is very nice. But it requires knowledge that the reader wouldn't have had in chapter 5. However, var with tuples was covered in chapter 4, so the following is within reach:

class Person(n: String) {
  val (firstName, lastName) = { val ns = n.split(" "); (ns(0), ns(1)) }
}