Scala local variable inside primary constructor - scala

Question

How in Scala I can define local variable in primary constructor?
I need to solve this exercise from Scala for the impatient book:
Write a class Person with a primary constructor that accepts a string
containing a first name, a space, and a last name, such as new
Person("Fred Smith"). Supply read-only properties firstName and
lastName. Should the primary constructor parameter be a var, a val, or
a plain parameter? Why?
And for now my solution looks like this:
class Person(firstLast: String) {
private[this] val firstLastAsArr = firstLast.trim.split(" ")
val firstName = firstLastAsArr (0)
val lastName = firstLastAsArr (1)
}
How I can restrict firstLastAsArr variable visibility to primary constructor scope (now it have class scope)?

Answer 1

One solution is to initialize firstName and lastName at once, thereby allowing to turn firstLastAsArr into a local temporary value inside your initialization block:
class Person(firstLast: String) {
val (firstName, lastName) = {
val firstLastAsArr = firstLast.trim.split(" ")
(firstLastAsArr(0), firstLastAsArr(1))
}
}

Answer 2

It is not a general answer, but in this particular way you may write:
val Array(firstName, lastName) = firstLast.trim.split(" ")

Answer 3

You don't strictly need the intermediate variable:
class Person(firstLast: String) {
val (firstName, lastName) =
firstLast.trim.split(" ") match {case Array(first, last) => (first, last)}
}
However, if your transformation from firstLast to firstName and lastName grows a big longer, for example, because you check that there is exactly one first and one last name, then I would encapsulate the whole splitting-business in a dedicated method:
class Person(firstLast: String) {
val (firstName, lastName) = split(firstLast)
private def split(firstLast: String): (String, String) = {
val firstLastAsArr = firstLast.trim.split(" ")
...
(first, last)
}
}

Answer 4

Pattern matching in constructor works just fine, but you should consider moving such logic from constructor to factory method:
case class Person(firstName: String, lastName: String)
object Person{
def apply(firstLast: String) = {
val firstLastAsArr = firstLast.trim.split(" ")
new Person(firstLastAsArr(0), firstLastAsArr(1))
}
}
val p = Person("My Title")

Answer 5

Pattern maching in primary constructor works well
class Person(_fullName:String) {
val (firstName, lastName) = _fullName.split(" ") match {
case Array(x:String, y:String, _*) => (x,y)
case _ => (null,null)
}
}
See my github for full answer
https://github.com/BasileDuPlessis/scala-for-the-impatient/blob/master/src/main/scala/com/basile/scala/ch05/Ex07.scala