CODEWITHSUNDEEP
scala
igx
igx

Reputation: 4231

getting the correct return type from typed function fails

I am trying to get proper type with a typed function e.g 

sealed trait Pet
case object Dog extends Pet
case object Cat extends Pet
case object Fish

def getPet[P >: Pet](pet: P) : P = {
  pet match{
    case Dog => Dog
    case Cat => Cat
  }
}

val d: Dog = getPet(Dog)//not compiled

any ideas ?

Upvotes: 0

Views: 57

Answers (1)

Mario Galic
Mario Galic

Reputation: 48410

Here is a typeclass example

sealed trait Pet
case object Dog extends Pet
case object Cat extends Pet
case object Fish extends Pet

trait PetFactory[P <: Pet] {
  def getPet(p: P): P
}

object PetFactory {
  def getPet[P <: Pet](p: P)(implicit petFactory: PetFactory[P]): P = petFactory.getPet(p)
  implicit val dogFactory: PetFactory[Dog.type] = (dog: Dog.type) => dog
  implicit val catFactory: PetFactory[Cat.type] = (cat: Cat.type) => cat
  implicit val fishFactory: PetFactory[Fish.type] = (fish: Fish.type) => fish
}

import PetFactory._

getPet(Dog)
getPet(Cat)
getPet(Fish)

which outputs

res0: Dog.type = Dog
res1: Cat.type = Cat
res2: Fish.type = Fish

Note that the type of singleton object O is O.type, for example

val fish: Fish.type = Fish

Upvotes: 6

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