Boxing & Unboxing

[Airslash]

Hello,

I'm still working on my self-aware classes for database communication, and I have an issue that I'd like to see clarified.

i've been reading some more about the C# programming, and came across the stuff regarding "boxing and unboxing" of variables. And if I understand that concept correctly, I think it applies to the following situation:

I have a class called Cell. It holds a string for the columnname and 2 objects for the value and the old_value.
I'm sure that if I obtain and store the data each time in these objects, I'm bound to disaster performance wise with the boxing & unboxing concept.
Is there a solution that allows me to store any kind of data in a variable without having to go around the boxing & unboxing stuff?

[Airslash]

I've worked around the problem by using Generics, but I think i've run into another problem now :)

Consider my class Cell :

   public class Cell<T> : ICloneable, IComparable, ISerializable, IXmlSerializable
    {
        #region Constructors

        /// <summary>
        /// Creates a new instance of the Cell class without setting
        /// a name of value.
        /// </summary>
        public Cell()
            : this(String.Empty, default(T))
        { }

        /// <summary>
        /// Creates a new instance of the Cell class with the specified
        /// name. The value will be set to null.
        /// </summary>
        /// <param name="name"></param>
        public Cell(string name)
            : this(name, default(T))
        { }

        /// <summary>
        /// Creates a new instance of the Cell class with the specified name
        /// and value.
        /// </summary>
        /// <param name="name">The name of the Cell.</param>
        /// <param name="value">The raw value of the Cell.</param>
        public Cell(string name, T value)
        {
            this.Name = name;
            this.Value = value;
            this.OldValue = default(T);
        }

        /// <summary>
        /// Creates a new instance of the Cell class with the information
        /// passed from the serialization context.
        /// </summary>
        /// <param name="info"></param>
        /// <param name="contect"></param>
        public Cell(SerializationInfo info, StreamingContext contect)
        {
            this.Name = info.GetString("Cell_Name");
            this.Value = (T)info.GetValue("Cell_Value", typeof(T));
            this.OldValue = (T)info.GetValue("Cell_OldValue", typeof(T));
        }

        #endregion

        #region Properties

        /// <summary>
        /// Gets or sets the name of the Cell.
        /// </summary>
        public string Name
        {
            get { lock (this) { return m_name; } }
            set { lock (this) { m_name = value; } }
        }

        /// <summary>
        /// Gets or sets the raw value of the Cell.
        /// </summary>
        public T Value
        {
            get { lock (this) { return m_value; } }
            set { lock (this) { this.OldValue = m_value; m_value = value; } }
        }

        /// <summary>
        /// Gets whether the contents of this Cell have been modified since
        /// it's creation.
        /// </summary>
        public bool Modified
        {
            get { lock (this) { return EqualityComparer<T>.Default.Equals(m_old_value); } }
        }

        /// <summary>
        /// Gets or sets the old value of the Cell.
        /// This function supports the NexusLink framework and should not be used/visible in your code.
        /// </summary>
        internal T OldValue
        {
            get { lock (this) { return m_old_value; } }
            set { lock (this) { m_old_value = value; } }
        }

        #endregion

        #region Private Fields

        private string m_name;      // The name of the Cell.
        private T m_value;          // The raw value of the Cell.
        private T m_old_value;      // The raw old value of the Cell.

        #endregion

        #region ICloneable Members

        /// <summary>
        /// Creates a deep copy of the current Cell by copying over
        /// all the internal datamembers in a bit-wise fashion.
        /// </summary>
        /// <returns>A Clone of the current Cell with the exact same data.</returns>
        public object Clone()
        {
            // Surround the function call with a lock so our datamembers cannot
            // be changed by another thread during the copy process.
            lock (this)
            {
                // To perform the deep clone operation we need a memorystream
                // and a formatter.
                MemoryStream sm = new MemoryStream();
                IFormatter bf = new BinaryFormatter();

                // Serialize our object into memory.
                bf.Serialize(sm, this);

                // Position the cursor in the memorystream at the beginning.
                sm.Seek(0, SeekOrigin.Begin);

                // Deserialize our object into something new.
                Cell<T> copy = (Cell<T>)bf.Deserialize(sm);

                // Release the memory.
                sm.Close();

                // Return the copy.
                return copy;
            }
        }

        #endregion

        #region IComparable Members

        /// <summary>
        /// Compares two Cells against each other based upon their name.
        /// </summary>
        /// <param name="obj">The object to compare against.</param>
        /// <returns>Less then zero if the name is less then the passed Cell's name; zero if both names are equal; Greather then zero if the name if more then the passed Cell's name.</returns>
        /// <exception cref="ArgumentException">The object 'obj' is not of type Cell.</exception>
        public int CompareTo(object obj)
        {
            // Surround the function call with a lock so our data
            // does not get altered by another thread during the call.
            lock (this)
            {
                // Convert the passed object to type Cell.
                Cell<T> temp = obj as Cell<T>;

                // First check if the passed object is of the same type.
                if (temp == null)
                {
                    throw new ArgumentException("The passed object 'obj' is not of type Cell");
                }

                // Cells are considered identical if there names match. Otherwise they
                // will be sorted in order of their name.
                return this.Name.CompareTo(temp.Name);
            }
        }

        #endregion

        #region ISerializable Members

        /// <summary>
        /// Allows the object to be serialized for transport or storage. This function stores
        /// all the required information from the object into the SerializationInfo object.
        /// The StreamingContext provides additional information about the destination of
        /// the serialization.
        /// </summary>
        /// <param name="info">The SerializationInfo object to hold the data.</param>
        /// <param name="context">Additional information about the destination of the serialization.</param>
        public void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            // Surround our call with a lock, because we don't want our
            // data changed during the retrieval process.
            lock (this)
            {
                // Add our data to the SerializationInfo object.
                info.AddValue("Cell_Name", this.Name);
                info.AddValue("Cell_Value", this.Value);
                info.AddValue("Cell_OldValue", this.OldValue);
            }
        }

        #endregion

        #region IXmlSerializable Members

        /// <summary>
        /// Only used by the DataSet in .NET, therefor this function always
        /// returns null because we're not a DataSet.
        /// </summary>
        /// <returns>null</returns>
        public System.Xml.Schema.XmlSchema GetSchema()
        {
            return null;
        }

        /// <summary>
        /// This function will read out the XML and rebuild the entire Cell object
        /// based upon the information stored in the XML.
        /// </summary>
        /// <param name="reader">The XmlReader to parse the XML document.</param>
        public void ReadXml(System.Xml.XmlReader reader)
        {
            // Consume the root element first of the XML file.
            reader.ReadStartElement();

            // Read the first attribute of the root element, this should be the name
            // of our Cell.
            this.Name = reader.GetAttribute("name");

            // Read the value of our cell next.
            reader.ReadStartElement("value");
            this.Value = (T)reader.ReadContentAs(typeof(T), null);
            reader.ReadEndElement();

            // Read the old value of cell.
            reader.ReadStartElement("oldvalue");
            this.OldValue = (T)reader.ReadContentAs(typeof(T), null);
            reader.ReadEndElement();

            // Consume the root end tag.
            reader.ReadEndElement();
        }

        /// <summary>
        /// This function will write out the attributes of our class
        /// into the XML file. Because we wish that a Cell is represented
        /// as a single element, we will add the values as attributes.
        /// </summary>
        /// <param name="writer">The XmlWriter to write the XML file.</param>
        public void WriteXml(System.Xml.XmlWriter writer)
        {
            // Write the name of our cell as an attribute in the root tag.
            // We always assume the root tag to be present.
            writer.WriteAttributeString("name", this.Name);

            // Now we will write the elements to contain the values of our Cell.
            // These will be childnodes of the Cell element.
            writer.WriteStartElement("value");
            writer.WriteValue(this.Value);
            writer.WriteEndElement();

            // As last step we write the "old value" of the Cell element.
            // Just like the "value" it's a child of Cell.
            writer.WriteStartElement("oldvalue");
            writer.WriteValue(this.OldValue);
            writer.WriteEndElement();

            // We never write the root elements.
        }

        #endregion
    }

Now I have a class Row, that holds a generic list of type Cell<T>, but I'm confused on how to properly work with or define the type T for Cell in my row.

    class Row : ICloneable, ISerializable, IXmlSerializable
    {
        public Row()
        { }

        internal Row(List<Cell<Type>> cells)
        { }

        public bool Add(Cell<Type> cell)
        { }

        public bool Remove(Cell<Type> cell)
        { }

        public bool Contains(Cell<Type> cell)
        { }

        internal bool ContainsModifiedCells()
        { }

        public Cell<Type> this[int index]
        { 
            get{}
        }

        public Cell<Type> this[string name]
        {
            get{}
        }

        public int Count
        {
            get { lock (this) { return m_cells.Count; } }
        }

        private List<Cell<Type>> m_cells;

Is this correct? The compiler is not complaining, but it looks so odd and confusing....

[Plater]

You are changing <Type> to the type you want right?
private List<Cell<Type> > m_cells;

[Airslash]

So using the "Type" class from reflection instead of just "T" will work?

The idea is to have a list of Cell<T> objects. Each Cell in the list should be able to have a different type at runtime. That's what I'm trying to achieve. I don't want to make my Row class Generic or type bound either, I just want to be able to do this for example:

Row r = new Row'();
r.AddCell(new Cell<int>("ID"));
r.AddCell(new Cell<string>("Name"));
r.AddCell(new Cell<object>("Image"));
r.AddCell(new Cell<int>("Amount"));
r.Commit();

That's what I'm trying to achieve, so I can reuse the single Cell class without having to worry about bocxing.unboxin g values when retrieving info from the database. Hope I made it clear what I'm trying to achieve.

[Plater]

Yeah I can see what you want, but List<Cell<Type> > will force your Cell objects to contain the Type class (or derived classes) and not Type T.

At some point I think you are going to have to box/unbox your entries if you want a collection with different types in it.

[Airslash]

any way around the issue then?

I tried defining them it as

List<Cell<T>> m_cells;

But this gives me compiler errors, saying something about namespace T not recognised.
Surely there must be a way to implement this without making my Row class Generic, or type bound?

[Plater]

If it were possible, I would think there would already be a class that does it?
You've pretty much just re-created the DataRow object right now