anchor.diff:      PhysicsBody bodyA,
       PhysicsBody bodyB,
       this.worldAnchor, {
  -      double lowerAngle: 0.0,
  -      double upperAngle: 0.0,
  -      bool enableLimit: false
  +      this.lowerAngle: 0.0,
  +      this.upperAngle: 0.0,
  +      this.enableLimit: false
       }) : super(bodyA, bodyB) {
  -    this.lowerAngle = lowerAngle;
  -    this.upperAngle = upperAngle;
  -    this.enableLimit = enableLimit;
  -
       _completeCreation();
     }
   
  -  Point worldAnchor;
  -  double lowerAngle;
  -  double upperAngle;
  -  bool enableLimit;
  +  final Point worldAnchor;
  +  final double lowerAngle;
  +  final double upperAngle;
  +  final bool enableLimit;
   
     box2d.Joint _createB2Joint(PhysicsNode physicsNode) {
       // Create Joint Definition
  
positive.code:     return physicsNode.b2World.createJoint(b2Def);
    }
  }
  
negative.code: class PhysicsJointWeld extends PhysicsJoint {
    PhysicsJointWeld(
      PhysicsBody bodyA,
      PhysicsBody bodyB
    ) : super(bodyA, bodyB) {
      _completeCreation();
    }
  
  