Question

I’m using a Logging trait in my application and I’m curious whether it’s possible to access a protected variable from the Logging trait.

This is what I have:

class MyClass extends ExternalTrait with Logging

trait ExternalTrait {
  protected val protectedVar = "secret?"
}

trait Logging {
  if(this.isInstanceOf[OtherTrait]) 
    this.asInstanceOf[OtherTrait].protectedVar
}

but the access to the protected variable is restricted when accessing in this manner. Is there some other way to access the protectedVar from the Logging trait?

Many thanks.

Answer 1

If you definitely know that Logging later is mixed in to ExternalTrait you can place a self reference:

trait Logging { this: ExternalTrait =>
  val value = protectedVar
}

Of course, if there can be logging traits which do not extend/mixin other traits self references are not suitable. In such a case I would subclass Logging to handle the different behavior.

trait Logging
trait StandAloneLogging extends Logging
trait BasedOnLogging extends Logging { this: ExternalTrait =>
  val value = protectedVar
}