game-0.dart

void main() {
  var circleSlot = new CircleSlot();
  circleSlot.insert(new Circle());
  
  var squareSlot = new SquareSlot();
  squareSlot.insert(new Square());
  
}

class Circle {}
class Square {}

class SquareSlot{
  insert (Square sqareSlot){
  }
}

class CircleSlot{
  insert (Circle circleSlot){
  }
}