CODEWITHSUNDEEP
scala
JohnBigs
JohnBigs

Reputation: 2811

use dynamic return type in a scala fuction

I have a function that gets a string with name of model and returning an instance of that case class, but im wondering what is the correct way to use dynamic return type here in this function?

case class Person(fname: String, lname: String)
case class Animal(type: String, weight: Double)

def getInstanceOf(model: String): ??? = model match {
    case "person" => Person("jack", "robinson")
    case "animal" => Animal("lion", 190.0)
}

thanks!

Upvotes: 0

Views: 1420

Answers (2)

medge
medge

Reputation: 608

It may help to have a bit more context of what the end goal is here to suggest a solution.

If your models all conform to a particular classification and you don't need to know exactly what instance they are then the abstract class (or trait) suggestion above should work.

EDIT: my original answer included this snippet:

You could also make the return type generic and put a type boundary on it in this scenario, such as:

def getInstanceOf[T <: Living](model: String): T = ...

But as pointed out below this allows the caller to specify what type they expect which may counteract what is contained in the model argument

If you only returned one of two possible types but needed the exact type then maybe an Either[T1, T2] would be appropriate here (http://www.scala-lang.org/api/current/scala/util/Either.html) such as:

def getInstanceOf(model: String): Either[Person, Animal] = ...

But again I think it would be easier to answer if the end goal was explained a bit

Upvotes: 6

akuiper
akuiper

Reputation: 215137

Maybe you can define an abstract class and extends both classes from it, and then you can specify the abstract class as the return type:

abstract class Living

case class Person(fname: String, lname: String) extends Living   
case class Animal(Type: String, weight: Double) extends Living

def getInstanceOf(model: String): Living = model match {
    case "person" => Person("jack", "robinson")
    case "animal" => Animal("lion", 190.0)
}
// getInstanceOf: (model: String)Living

Upvotes: 6

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