map-display/include/kml/dom/visitor_driver.h

// Copyright 2009, Google Inc. All rights reserved.
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// WARNING: THE VISITOR API IMPLEMENTED IN THIS CLASS IS EXPERIMENTAL AND
// SUBJECT TO CHANGE WITHOUT WARNING.

#ifndef KML_DOM_VISITOR_DRIVER_H__
#define KML_DOM_VISITOR_DRIVER_H__

#include "kml/base/util.h"
#include "kml/dom/kml_ptr.h"
#include "kml/dom/visitor.h"

namespace kmldom {

// A visitor driver controls the flow of a visitation over the dom element
// hierarchy. There is typically expected to be only a single driver for each
// visitation and currently there is not concept of chaining drivers (though
// visitors themselves could be chained within a single 'multi driver').
class VisitorDriver {
 protected:
  VisitorDriver();
  virtual ~VisitorDriver();

 public:
  // Handles the visitation of the subtree of elements rooted at the given
  // element. This method is invoked either by the user to initiate a visitation
  // or in response to a call to AcceptChildren() for an element.
  //
  // Typically when a driver visits an element it will, in some order:
  // - call accept() on the given element for some set of visitors
  // - call acceptChildren() on the given element, passing itself
  // However there is no requirement that either of these actually occur and
  // the driver is free to implement whatever semantics it chooses.
  virtual void Visit(const ElementPtr& element) = 0;
  LIBKML_DISALLOW_EVIL_CONSTRUCTORS(VisitorDriver);
};

// A simple driver implementation that invokes a single visitor in pre-order
// traversal of an element hierarchy. The visitor will visit each element in a
// hierarchy before that element's children are visited.
class SimplePreorderDriver : public VisitorDriver {
 public:
  explicit SimplePreorderDriver(Visitor* visitor);
  virtual ~SimplePreorderDriver();

  virtual void Visit(const ElementPtr& element);

 private:
  Visitor* visitor_;
  LIBKML_DISALLOW_EVIL_CONSTRUCTORS(SimplePreorderDriver);
};


// A simple driver implementation that invokes a single visitor in post-order
// traversal of an element hierarchy. The visitor will visit each element in a
// hierarchy after that element's children have been visited.
class SimplePostorderDriver : public VisitorDriver {
 public:
  explicit SimplePostorderDriver(Visitor* visitor);
  virtual ~SimplePostorderDriver();

  virtual void Visit(const ElementPtr& element);

 private:
  Visitor* visitor_;
  LIBKML_DISALLOW_EVIL_CONSTRUCTORS(SimplePostorderDriver);
};

}  // namespace kmldom

#endif  // KML_DOM_VISITOR_DRIVER_H__