CODEWITHSUNDEEP
scala
Ed Brannin
Ed Brannin

Reputation: 7901

How can I return a scala "object" as if it's a class instance?

I have an abstract superclass with a variety of stateless implementations. It seems like the thing to do is make the abstract superclass a class, and make each implementation an object because I only ever need one of each.

This is a toy example, but it shows the compile error I’m getting:

// Tramsformer.scala

class Transformer {
  def transform(value : String) : String
}

object Transformer {
  getTransformer(String : name) : Transformer = {
    name match {
      case "upper" => UpperTransformer
                      // I'm getting "Cannot Resolve Symbol" on UpperTransformer, 
                      // even though they're in the same package.
      case _ => throw new IllegalArgumentException("...")
    }
  }
}

// ---
// UpperTransformer.scala is in the same package
object UpperTransformer extends Transformer {
  override def transform(vlaue : String) = foo.toUpperCase()
}

I’m really shooting for some sort of dynamic dispatch on (dataProvider, desiredAction) here.

Then some class can call Transformer.getTransformer("upper").transform("stack-overflow") without making any unnecessary objects.

Any idea what I should be doing differently? Should I stop worrying about premature optimization and learn to love the instance?

Upvotes: 0

Views: 224

Answers (1)

sepp2k
sepp2k

Reputation: 370435

The problem isn't visibility, it's that you simply do not define an object named UpperTransformer anywhere - only a class. If you replace class UpperTransformer with object UpperTransformer, your code should work fine.

Upvotes: 2

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