Scala class: avoid parameters while creating new instance - scala

Question

Suppose I have 2 files.
myMainApplication.scala
printInfos.scala
Briefly myMainApplication.scala contains
val name = "blah"
val age= 45
Briefly my class myMainApplication.scala should print out the name and the age by creating a new printInfos instance. However I should not add any parameters while creating the instance.
What I would like to AVOID:
Inside printInfos.scala
class printInfos(val myName: String,
val myAge: Int
val myLoc: String
val myNPP: Double
val myCountry: String
val myProvice: String
val myNPAP: String) {
def printInfos() = {
println("Your method printInfos print out" + myName + myAge + myLoc + myNPP + myCountry + myProvice + myNPAP)
}
}
Inside myMainApplication.scala
val name = "blah"
val age= 45
val loc = "blah"
val npp = 45.5
val country = "germany"
val province = "bayern"
val npap = "blaha"
// want to avoid to enter so many params
val printInfoInstance = new printInfos(name, age, loc, npp, country, province, npap)
printInfoInstance.printInfos()
I would like to get something similar:
Inside printInfos.scala
class printInfos() {
var myName: String = 0
var myAge: Int = 0
var myLoc: String = 0
var myNPP: Double = 0
var myCountry: String = 0
var myProvice: String = 0
var myNPAP: String = 0
def printInfos() = {
println("Your method printInfos print out" + myName + myAge + myLoc + myNPP + myCountry + myProvice + myNPAP)
}
}
Inside myMainApplication.scala
// want to create new instance with no params at begining
val printInfoInstance = new printInfos()
val name = "blah"
printInfoInstance.myName() = name
val age= 45
printInfoInstance.myAge() = age
val loc = "blah"
printInfoInstance.myLoc() = loc
val npp = 45.5
printInfoInstance.myNPP() = npp
val country = "germany"
printInfoInstance.myCountry() = country
val province = "bayern"
printInfoInstance.myProvice() = province
val npap = "blaha"
printInfoInstance.myNPAP() = npap
printInfoInstance.printInfos
Looking for improvements
Would it be possible to get something similar to the second proposal but avoiding to use var ? However, the final aim is still to avoid adding a lot of parameters when creating a new intance.

Answer 1

I'd suggest you use scala's case classes for this. It provides a copy method that allows you to create a new instance with the changed parameters. This keeps everything immutable. Note that you don't have to update all of the parameters - you could just do one at a time.
case class printInfos(myName: String = "",
myAge: Int = 0,
myLoc: String = "",
myNPP: Double = 0,
myCountry: String = "",
myProvince: String = "",
myNPAP: String = "") {
def printInfos() = {
println("Your method printInfos print out" + myName + myAge + myLoc + myNPP + myCountry + myProvince + myNPAP)
}
}
val printInfoInstance = new printInfos()
val name = "blah"
val age= 45
val loc = "blah"
val npp = 45.5
val country = "germany"
val province = "bayern"
val npap = "blaha"
val newInstance = printInfoInstance.copy(
myName = name,
myAge = age,
myLoc = loc,
myNPP = npp,
myCountry = country,
myProvince = province,
myNPAP = npap
)
newInstance.printInfos()

Answer 2

In addition to what #longshorej has mentioned, provided you have a case class defined. you can instantiate without the new keyword:
printInfos("name","age","loc","npp","country","province","npap") would create a new instance.
For the printing part I'd suggest overriding toString so that it aligns well with standard nomenclature.

Answer 3

It is a benefit of the type system to be able to require all the parameters needed to create a valid instance of a class.
If you want to avoid the verbosity of passing all the parameters every time, you can provide default values for them (only a good idea if they are truly optional, as you really want to avoid invalid intermediate states).
// assuming it doesn't make sense to instantiate without
// a few required parameters
case class InfoPrinter (
name: String, // required
age: Int, // required
loc: String = "",
NPP: Double = 0,
country: String = "",
province: String = "",
NPAP: String = ""
) {
def printInfos =
println(s"Your method printInfos print out $name $age $loc $NPP $country $province $NPAP")
}
You can then use it like this:
// named params or positionally
InfoPrinter("blah", 45, country="germany", province="bayern").printInfos
Any parameters with default values can be omitted.