delayedInt experimentation

delayedInt.scala

/*
  scala version := 2.10.3
  
  After running into some problems with the App trait which extends the DelayedInt trait,
  I've done some testing to see what is happening. There were some interesting subtleties
  that I previously overlooked.
  
  KEEP IN MIND THIS: https://issues.scala-lang.org/browse/SI-4680
    - Empty constructors cause delayedInit to not be invoked (some examples illustrate this)
*/

trait Stage1 extends DelayedInit {
  println("Stage1 constructor")

  override def delayedInit(x: => Unit) {
    println("Stage1 delayedInit before x")
    x
    println("Stage1 delayedInit after x")
  }
}

trait Stage2 {
  println("Stage2 constructor")
}

trait Stage3 {
  println("Stage3 constructor")
}

trait Stage123 extends Stage1 with Stage2 with Stage3 {
  println("Stage123 constructor")
}

trait Stage1Di23 extends Stage1 {
  this: Stage2 with Stage3 =>
  println("Stage1Di23 constructor")
}

trait Stage12Di3 extends Stage1 with Stage2 {
  this: Stage3 =>
  println("Stage12Di3 constructor")
}

/*
Stage1 constructor
Stage2 constructor
Stage3 constructor
Stage123 constructor
Main application constructor end
 */
object Main123 extends App {
  println("Main application constructor start")
  new Stage123 {}
  println("Main application constructor end")
}

/*
Main application constructor start
Stage1 constructor
Stage2 constructor
Stage3 constructor
Stage123 constructor
Stage1 delayedInit before x
Stage123 NonEmpty constructor
Stage1 delayedInit after x
Main application constructor end
 */
object Main123NonEmpty extends App {
  println("Main application constructor start")
  new Stage123 {
    println("Stage123 NonEmpty constructor")
  }
  println("Main application constructor end")
}

/*
Main application constructor start
Stage1 constructor
Stage1Di23 constructor
Stage2 constructor
Stage3 constructor
Main application constructor end
 */
object Main1Di23 extends App {
  println("Main application constructor start")
  new Stage1Di23 with Stage2 with Stage3 {}
  println("Main application constructor end")
}

/*
Main application constructor start
Stage1 constructor
Stage1Di23 constructor
Stage2 constructor
Stage3 constructor
Stage1 delayedInit before x
Stage1Di23 NonEmpty constructor
Stage1 delayedInit after x
Main application constructor end
 */
object Main1Di23NonEmpty extends App {
  println("Main application constructor start")
  new Stage1Di23 with Stage2 with Stage3 {
    println("Stage1Di23 NonEmpty constructor")
  }
  println("Main application constructor end")
}

/*
Main application constructor start
Stage1 constructor
Stage2 constructor
Stage12Di3 constructor
Stage3 constructor
Stage1 delayedInit before x
Stage12Di3 NonEmpty constructor
Stage1 delayedInit after x
Main application constructor end
 */
object Main12Di3NonEmpty extends App {
  println("Main application constructor start")
  new Stage12Di3 with Stage3 {
    println("Stage12Di3 NonEmpty constructor")
  }
  println("Main application constructor end")
}


trait StageCakeComponent {
  val stage: StageCake

  trait StageCake {
    def printStage() {
      println("StageComponent Stage constructor")
    }
  }

}

trait Stage1CakeComponent extends StageCakeComponent {
  override val stage: Stage1Cake

  trait Stage1Cake extends StageCake {
    override def printStage() {
      println("Stage1 constructor")
    }
  }

}

trait Stage2CakeComponent extends StageCakeComponent {
  override val stage: Stage2Cake

  trait Stage2Cake extends StageCake {
    override def printStage() {
      println("Stage2 constructor")
    }
  }

}

trait CakeDiStage1 {
  this: StageCakeComponent with Stage1 =>
  println("CakeDiStage1 constructor")
}

trait CakeDiStage12 {
  this: StageCakeComponent with Stage1 with Stage2 =>
  println("CakeDiStage12 constructor")
}

trait Stage1CakeDiStage2 extends Stage1 {
  this: StageCakeComponent with Stage2 =>
  println("CakeStage1DiStage2 constructor")
}

/*
Main application constructor start
CakeDiStage1 constructor
Stage1 constructor
Stage1 delayedInit before x
Stage1Cake NonEmpty constructor
Stage1 delayedInit after x
Main application constructor end
 */
object MainCakeDi1With1WithComp1 extends App {
  println("Main application constructor start")
  new CakeDiStage1 with Stage1 with Stage1CakeComponent {
    override val stage = new Stage1Cake {
      println("Stage1Cake NonEmpty constructor")
    }
  }
  println("Main application constructor end")
}

/*
Main application constructor start
CakeDiStage1 constructor
Stage1 constructor
Stage2 constructor
Stage1 delayedInit before x
Stage2Cake NonEmpty constructor
Stage1 delayedInit after x
Main application constructor end
 */
object MainCakeDi1With1With2WithComp2 extends App {
  println("Main application constructor start")
  new CakeDiStage1 with Stage1 with Stage2 with Stage2CakeComponent {
    override val stage = new Stage2Cake {
      println("Stage2Cake NonEmpty constructor")
    }
  }
  println("Main application constructor end")
}

/*
Main application constructor start
CakeDiStage1 constructor
Stage2 constructor
Stage1 constructor
Stage1 delayedInit before x
Stage2Cake NonEmpty constructor
Stage1 delayedInit after x
Main application constructor end
 */
object MainCakeDi1With2With1WithComp2 extends App {
  println("Main application constructor start")
  new CakeDiStage1 with Stage2 with Stage1 with Stage2CakeComponent {
    override val stage = new Stage2Cake {
      println("Stage2Cake NonEmpty constructor")
    }
  }
  println("Main application constructor end")
}

/*
Main application constructor start
CakeDiStage12 constructor
Stage1 constructor
Stage2 constructor
Stage1 delayedInit before x
Stage1Cake NonEmpty constructor
Stage1 delayedInit after x
Main application constructor end
 */
object MainCakeDi12With1With2WithComp1 extends App {
  println("Main application constructor start")
  new CakeDiStage12 with Stage1 with Stage2 with Stage1CakeComponent {
    override val stage = new Stage1Cake {
      println("Stage1Cake NonEmpty constructor")
    }
  }
  println("Main application constructor end")
}