CODEWITHSUNDEEP
scalainstancerequiretraits
Antoine Martin
Antoine Martin

Reputation: 1953

Consider a trait as a subclass of another class

my question below is definately a nonsense but answering it will help me for another problem. How force a trait to be mixed only by a specific class (or its subclass). I thought about use require() inside it :

abstract class Aclass(c_attribut1 : Int){
  var attribut1 : Int = c_attribut1

  def getAttribut1() : Int = this.attribut1 
}

class Bclass extends Aclass(1) with Trait1{

}

class Cclass extends Aclass(2) with Trait1{

}


trait Trait1{
  require(this.isInstanceOf[Aclass]);

  def f() : Int = this.getAttribut1() * 2 // it obviously does not work
}

Then, I don't know how considere Trait1 as a Aclass (in order to avoid asInstanceOf every where). I know the function f should be in the Aclass but, as I said, I would like to know how properly force a trait to be mixed by a specific class and how to get messages of this class in the trait.

I wonder this because I need a trait is mixed by a specific class with template :

trait TraitBuiltHost extends Observable{
  require(this.isInstanceOf[BuiltInfrastructure[_ <: TraitHostDefinition]]);
  .
  .
  .
}

Thank you.

Upvotes: 2

Views: 142

Answers (1)

senia
senia

Reputation: 38045

Self typing:

class MyClass1
class MyClass2

trait MyTrait {
  self: MyClass1 =>
  val i = 1
}

scala> new MyClass1 with MyTrait
res0: MyClass1 with MyTrait = $anon$1@3f0762f6

scala> new MyClass2 with MyTrait
<console>:1: error: illegal inheritance;
 self-type MyClass2 with MyTrait does not conform to MyTrait's selftype MyTrait with MyClass1
              new MyClass2 with MyTrait
                                ^

See also Self references part of scala tag wiki.

Upvotes: 4

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