For use with CMSC-341, Spring 99,  Project 2

Here is the definition of the List class. 

Copy it to your List.H file. 

Remember:
 -- implement the inline method(s)
 -- guard the file
 -- complete the documentation
------------------------------------------------

/*
   Interface for List.
   Author: Thomas Anastasio
   Version: 5 February 1999
*/
template <class T>
class List
{
private:
  int _length;  // number of elements in the list
protected:
  inline void SetLength(int len);
public:
  // Adds element x at position pos of this list, causing previous 
  // elements at positions >= pos to move up. The lowest position is 1.  
  // Param: x the element to be inserted.
  // Param: pos the position at which to place x 
  //     ( 0 < pos <= list_length + 1)
  // Return: true if insertion succeeds, false otherwise.
  virtual bool Insert(const T& x, int pos) = 0;

  // Adds element x at the end of this list.
  // Param: x the element to be appended.
  // Return: true if succeeds, false otherwise.
  virtual bool Append(const T& x) = 0;

  // Accesses the element at the specified position in this list.
  // Param: pos the position at which to retrieve the element.
  // Return: the element at pos.
  // Pre-condition: pos is a valid position
  //     ( 0 < pos <= list_length)
  // It is an error to attempt to retrieve an element from an
  //    invalid position.
  virtual T& Retrieve(int pos) = 0;

  // Deletes the element at the specified position in this list.
  // Param: pos the position at which to delete the element.
  //     ( 0 < pos <= list_length)
  // Return: true if deletion succeeds, false otherwise. Deletion
  // from an empty list returns false.
  virtual bool Delete(int pos) = 0;

  // Accessor for the size of this list.
  // Return: the number of elements on this list.
  inline int Length() const;

  // Test for this list being empty.
  // Return: true if this list is empty, false otherwise.
  bool IsEmpty() const;

  // Makes this list be empty
  virtual void MakeEmpty() = 0;

  // A string describing this list.  For example, the string
  // describing a LinkedList would be "LinkedList"
  // Return: a string description
  virtual char * ToString() = 0;

  // Accessor for a forward iterator over the list.
  // Traversal direction is forward (head to tail).
  // Return: ptr to the Iterator.
  // Note: allocated on the heap.  User is responsible for
  // storage deallocation.
  virtual Iterator<T> * GetIterator() = 0;

  // Accessor for a reverse iterator over the list.
  // Traversal direction is reverse (tail to head).
  // Return: ptr to the Iterator.
  // Note: allocated on the heap.  User is responsible for
  // storage deallocation.
  virtual Iterator<T> * GetReverseIterator() = 0;
};

// Output stream operator that works for any List.
// Writes the elements of the list in the textbook's style (a
// comma-separated list of elements inside parenthesis).  For
// example the list containing the elements 1, 2, and 3 would
// be printed as   (1,2,3)
template<class T>
ostream& operator<< (ostream &,  List<T> &);