text: // -*-Mode: C++;-*-
  
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  //***************************************************************************
  // StackableIterator.h
  //
  //   a base set of functionality for iterators that can be used with the
  //   IteratorStack abstraction to traverse nested structures 
  //
  // Author: John Mellor-Crummey                                
  //
  // Creation Date: October 1993
  //
  //***************************************************************************
  
  
  #ifndef StackableIterator_h
  #define StackableIterator_h
  
  //************************** System Include Files ***************************
  
  //*************************** User Include Files ****************************
  
  #include <include/uint.h>
  
  //*************************** Forward Declarations **************************
  
  //***************************************************************************
  // class StackableIterator
  //***************************************************************************
  
  class StackableIterator {
  public:
    StackableIterator();
    virtual ~StackableIterator();
  
    //----------------------------------------------------------------------
    // upcall to get the value of the current element in the iteration from 
    // a derived iterator 
    //----------------------------------------------------------------------
    virtual void *CurrentUpCall() const = 0;
  
    //----------------------------------------------------------------------
    // upcall to advance the iteration
    //----------------------------------------------------------------------
    virtual void operator++() = 0; // prefix increment
    void operator++(int);          // postincrement via preincrement operator
  
    //----------------------------------------------------------------------
    // predicate to test if the value returned by CurrentUpCall is valid.
    // supplied default implementation returns true if the value is non-zero 
    //----------------------------------------------------------------------
    virtual bool IsValid() const; 
  
    //----------------------------------------------------------------------
    // upcall to restart the iteration at the beginning
    //----------------------------------------------------------------------
    virtual void Reset() = 0;
  
    //----------------------------------------------------------------------
    // dump essential state (class name, this pointer, currrent iterate) 
    // and invoke DumpUpCall to report interesting state of derived class
    //----------------------------------------------------------------------
    void Dump();
  
  private:
    //----------------------------------------------------------------------
    // upcall to dump any interesting state of a derived class 
    //----------------------------------------------------------------------
    virtual void DumpUpCall();
  };
  
  #endif
  
  