PlanWalker encapsulates the logic to traverse a plan. It is used only by
All walkers must be constructed in a way that they only visit a given node
once in a traversal.
plan Plan for this walker to traverse.
Begin traversing the graph.
visitor Visitor this walker is being used by. This can't be set in
the constructor because the visitor is constructing this class, and does
not yet have a 'this' pointer to send as an argument.
VisitorException if an error is encountered while walking.
Return a new instance of this same type of walker for a subplan.
When this method is called the same type of walker with the
provided plan set as the plan, must be returned. This can then be
used to walk subplans. This allows abstract visitors to clone
walkers without knowning the type of walker their subclasses used.
plan Plan for the new walker.
- Instance of the same type of walker with mPlan set to plan.