CODEWITHSUNDEEP
scalaimplicit
Dennis Hunziker
Dennis Hunziker

Reputation: 1293

Could not find implicit when used in main method

I've got code similar to the following extract:

object Obj {
  case class Dog(colour: String= "brown")

  def summon(dog: Dog = Dog()): Dog = dog

  def getColour(implicit d: Dog): String = d.colour

  def main(args: Array[String]): Unit = {
    implicit val dog = summon(Dog(colour = "orange"))

    val colour = getColour
  }
}

This doesn't compile because the compiler can't find an implicit dog for parameter d when calling getColour. The strange thing though is that if I try to assign the result of getColour to a val named something other than colour it works. Also if I move the 2 lines out of the main method it works as well. Any ideas what's causing the implicit resolution to fail here?

I'm using Scala version 2.12.6.

Upvotes: 4

Views: 101

Answers (1)

Mario Galic
Mario Galic

Reputation: 48410

If we remove implicit like so

  def main(args: Array[String]): Unit = {
    val dog = summon(Dog(colour = "orange"))
    val colour = getColour(dog) // error: recursive value dog needs type
  }

we get recursive value dog needs type, so I believe this is an instance of

https://issues.scala-lang.org/browse/SI-5091

Upvotes: 3

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