CODEWITHSUNDEEP
scala
d-_-b
d-_-b

Reputation: 4502

How can I explicitly tell the compiler what the return type is?

Suppose I have an abstract class and an object of the same name in the same file.

How can I explicitly tell the compiler that the return type of run is the abstract class CommandResult type not the object CommandResult type?

Base.scala

trait Base {
  def run[T]: Future[T]
}

X.scala

class X extends Base {
  override def run[CommandResult]: Future[CommandResult] = {
      // here return CommandResult, Success or Failure
  }
}

sealed abstract class CommandResult(val exitCode: Int)

object CommandResult {
  case object Success extends CommandResult(0)
  case object Failure extends CommandResult(1)
}

Upvotes: 0

Views: 55

Answers (1)

pedrofurla
pedrofurla

Reputation: 12783

When you write def run[CommandResult], it means "run takes a type one parameter named CommandResult", that's why you are getting error like:

On line 3: error: type mismatch;
        found   : CommandResult.Success.type
        required: CommandResult              <--- The type parameter, 
                                              not the class or object.

The error indeed is very misleading. For example try override def run[X]: Future[X] and will see "required: X`.

If you do as Luis suggests:

trait Base[T] {
  def run: Future[T]
}

class X extends Base[CommandResult] {
  override def run: Future[CommandResult] = {
      Future(CommandResult.Success)
  }
}

It will work.

Upvotes: 1

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