anchor.diff:      this.anchorA,
       this.anchorB,
       this.ratio, {
  -      double breakingForce
  -    }
  -  ) : super(bodyA, bodyB, breakingForce) {
  +      double breakingForce,
  +      PhysicsJointBreakCallback breakCallback
  +    }
  +  ) : super(bodyA, bodyB, breakingForce, breakCallback) {
       _completeCreation();
     }
   
  
positive.code:     this.anchorA,
      this.anchorB, {
        double breakingForce,
        this.length,
        this.dampening: 0.0,
        this.frequency: 0.0
      }
    ) : super(bodyA, bodyB, breakingForce) {
      _completeCreation();
    }
  
  
negative.code: part of skysprites;
  
  typedef void PhysicsJointBreakCallback(PhysicsJoint joint);
  
  abstract class PhysicsJoint {
    PhysicsJoint(this._bodyA, this._bodyB, this.breakingForce, this.breakCallback) {
      bodyA._joints.add(this);
      bodyB._joints.add(this);
    }
  