//
//   This file contains the C# code from Program 6.11 of
//   "Data Structures and Algorithms
//    with Object-Oriented Design Patterns in C#"
//   by Bruno R. Preiss.
//
//   Copyright (c) 2001--2002 by Bruno R. Preiss, P.Eng.  All rights reserved.
//
//   http://www.brpreiss.com/books/opus6/programs/pgm06_11.txt
//
public class StackAsLinkedList : AbstractContainer, Stack
{
    protected LinkedList list;

    private class Enumerator : IEnumerator
    {
	StackAsLinkedList stack;
	protected LinkedList.Element position = null;

	internal Enumerator(StackAsLinkedList stack)
	    { this.stack = stack; }

	public bool MoveNext()
	{
	    if (position == null)
		position = stack.list.Head;
	    else
		position = position.Next;
	    return position != null;
	}

	public object Current
	{
	    get
	    {
		if (position == null)
		    throw new InvalidOperationException();
		return position.Datum;
	    }
	}
	
	public void Reset()
	    { position = null; }
    }

    public override IEnumerator GetEnumerator()
	{ return new Enumerator(this); }
    // ...
}