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Persistent Data Structures

, 23 Feb 2005
An article describing the basic principles of persistent data structures.
persistentdatastructures_src.zip
ImmutableCollections
ImmutableCollections
AVL Tree Classes
ImmutableCollections.csproj.user
RAL Helper Classes
/*
 * Created by: Leslie Sanford 
 * 
 * Last modified: 02/23/2005
 * 
 * Contact: jabberdabber@hotmail.com
 */

using System;
using System.Collections;
using System.Diagnostics;

namespace ImmutableCollections
{
	/// <summary>
	/// Represents the top nodes in a RandomAccessList.
	/// </summary>
	internal class RalTopNode
	{
        #region RalTopNode Members

        #region Instance Fields

        // The root of the tree the top node represents.
        private readonly RalTreeNode root;

        // The next top node in the list.
        private readonly RalTopNode nextNode;

        #endregion

        #region Construction

        /// <summary>
        /// Initializes a new instance of the RalTopNode with the specified 
        /// root of the tree this node represents and the next top node in the
        /// list.
        /// </summary>
        /// <param name="root">
        /// The root node of the tree this top node represents.
        /// </param>
        /// <param name="nextNode">
        /// The next top node in the list.
        /// </param>
		public RalTopNode(RalTreeNode root, RalTopNode nextNode)
		{
            Debug.Assert(root != null);

            this.root = root;
            this.nextNode = nextNode;
		}

        #endregion

        #region Methods

        /// <summary>
        /// Gets the value at the specified element in the random access list.
        /// </summary>
        /// <param name="index">
        /// An integer that represents the position of the random access list 
        /// element to get. 
        /// </param>
        /// <returns>
        /// The value at the specified position in the random access list.
        /// </returns>
        public object GetValue(int index)
        {            
            int i = index;
            RalTopNode currentNode = this;

            // Find the top node containing the specified element.
            while(i >= currentNode.Root.Count)
            {
                i -= currentNode.Root.Count;
                currentNode = currentNode.NextNode;

                Debug.Assert(currentNode != null);
            }

            return currentNode.Root.GetValue(i);
        }

        /// <summary>
        /// Sets the specified element in the current random access list to the 
        /// specified value.
        /// </summary>
        /// <param name="value">
        /// The new value for the specified element. 
        /// </param>
        /// <param name="index">
        /// An integer that represents the position of the random access list  
        /// element to set. 
        /// </param>
        /// <returns>
        /// A new random access list top node with the element at the specified 
        /// position set to the specified value.
        /// </returns>
        public RalTopNode SetValue(object value, int index)
        {
            RalTopNode result;

            // If the element is in the tree represented by the current top 
            // node.
            if(index < Root.Count)
            {
                // Descend into the tree.
                result = new RalTopNode(
                    root.SetValue(value, index), 
                    NextNode);
            }
            // Else the element is further along in the list.
            else
            {
                // Move to the next top node.
                result = new RalTopNode(
                    root, 
                    NextNode.SetValue(value, index - Root.Count));
            }

            return result;
        }

        #endregion

        #region Properties

        /// <summary>
        /// Gets the root node represented by the top node.
        /// </summary>
        public RalTreeNode Root
        {
            get
            {
                return root;
            }
        }
        
        /// <summary>
        /// Gets the next top node in the random access list.
        /// </summary>
        public RalTopNode NextNode
        {
            get
            {
                return nextNode;
            }
        }

        #endregion

        #endregion
	}
}

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About the Author

Leslie Sanford

United States United States
Aside from dabbling in BASIC on his old Atari 1040ST years ago, Leslie's programming experience didn't really begin until he discovered the Internet in the late 90s. There he found a treasure trove of information about two of his favorite interests: MIDI and sound synthesis.
 
After spending a good deal of time calculating formulas he found on the Internet for creating new sounds by hand, he decided that an easier way would be to program the computer to do the work for him. This led him to learn C. He discovered that beyond using programming as a tool for synthesizing sound, he loved programming in and of itself.
 
Eventually he taught himself C++ and C#, and along the way he immersed himself in the ideas of object oriented programming. Like many of us, he gotten bitten by the design patterns bug and a copy of GOF is never far from his hands.
 
Now his primary interest is in creating a complete MIDI toolkit using the C# language. He hopes to create something that will become an indispensable tool for those wanting to write MIDI applications for the .NET framework.
 
Besides programming, his other interests are photography and playing his Les Paul guitars.

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