IPAddress class serializable?

Back in 2002 I posted a question in Usenet about the IPAddress class being serializable, but not serializing in ASP.NET. I just found the post, and noticed that no one responded with the reason why. So, here it is:

There are two types of serialization in .NET: System.Runtime.Serialization and System.Xml.Serialization. Runtime serialization uses the serializable attribute while XML serialization does not. Since ASP.NET uses XML serialization, the attribute was irrelevant.

The error I received was:

System.Net.IPAddress cannot be serialized because it does not have a default public constructor

One of the requirements of the XmlSerializer is that the class it is trying to serialize must have a default public constructor.

Is it reference or value equality?

Probably reference. Checking for value equality is unintuitive - by default == is a reference equality check.

object a = 1;

object b = 1;

Assert.IsFalse (a == b);

Object a doesn't equal object b since boxing a as object created once instance, and boxing b created another. Since == is a "reference type equality operator", it will only compare the references.

Using any of these methods works fine:

Assert.IsTrue (a.Equals (b));

Assert.IsTrue (((int)a).Equals (b));

Assert.IsTrue (Object.Equals (a, b));

Assert.IsTrue ((int)a == (int)b);

When passing objects around, the simple solution is to use the Equals() method as it may perform value equality if the object overrides Equals(). So, value equality is somewhat easy to accomplish for individual objects, but you run into this problem again with collections:

Assert.IsFalse (

    new string[] { "abc", "def" }.Equals (

    new string[] { "abc", "def" }));

Assert.IsFalse (new int[] { 1, 2, 3 }.Equals (new int[] { 1, 2, 3 }));

Assert.IsFalse (

    new object[] { 4, "stuff", DateTime.Parse ("1/1/2004 1:00 AM") }.Equals (

    new object[] { 4, "stuff", DateTime.Parse ("January 1, 2004 01:00") }));

There is only reference equality with ArrayList since Object.Equals() is inherited not overridden.

Assert.IsFalse (

    new System.Collections.ArrayList (new int[] { 1, 2, 3 }) == 

    new System.Collections.ArrayList (new int[] { 1, 2, 3 }));

Assert.IsFalse (

    new System.Collections.ArrayList (new int[] { 1, 2, 3 }).Equals (

    new System.Collections.ArrayList (new int[] { 1, 2, 3 })));

Here's my solution to perform value equality for collections. And now:

Assert.IsTrue (Collection.Equals (

    new System.Collections.ArrayList (new int[] { 1, 2, 3 }), 

    new System.Collections.ArrayList (new int[] { 1, 2, 3 }), true));

Assert.IsTrue (Collection.Equals (

    new int[] { 1, 2, 3 }, new System.Collections.ArrayList (

    new int[] { 1, 2, 3 }), true));

Assert.IsTrue (Collection.Equals (

    new object[] { 1, 2, 3 }, 

    new int[] { 1, 2, 3 }), true);

Assert.IsTrue (Collection.Equals (

    new object[] { 4, "stuff", DateTime.Parse ("1/1/2004 1:00 AM") }, 

    new object[] { 4, "stuff", DateTime.Parse ("January 1, 2004 01:00") }), true);

Here's a real world example:

/// <summary>Always accepts the public key hardcoded in the byte array as a valid certificate.</summary>

public sealed class AcceptTrustedCertificate : ICertificatePolicy {

    public bool CheckValidationResult (

        ServicePoint srvPoint,

        X509Certificate certificate,

        WebRequest request,

        int certificateProblem) {

        //TODO: verify certificateProblem is an acceptable value

        // return true if certificate returned is equal to the certificate's public key

        return Collection.Equals (

            certificate.GetPublicKey (),

            new byte[] { 48, 130, 1, 10, 2, 130, 1, 1, 0, 206, 214, 212 }, true);

    }

}

XML/object libraries are deprecated

If you take any one of the many RSS libraries, including my own RSS.NET, ATOM libraries, or even OPML libraries, you find mostly the same functionality. Each read and write to a specific XML format. Some take advantage of the XML libraries provided by the environment, and some even read and write through streams. But they all solve the same problem - reading and writing objects or structures to and from an XML file, abstracting away XML from the client.

From my experience with RSS.NET, I believe that this code is useless. These formats will eventually evolve and new formats will arise. These libraries should evolve to solve a different problem: generating libraries that read and write specific XML formats.

Armed with a XML schema and an object mapping XML file, this new type of library should be able to generate libraries themselves whose purpose is to read and write to a specific XML file format. After this assembly is produced, developers can use this "strongly typed" object and its formatReader and formatWriter objects to read and write documents. Since this library would use code generation, developers would code this library against the XML schema standard, resulting in generic code that could be applied to any XML format.



The result could be RSS, ATOM, and OPML objects who can read and write their respective formats a piece at a time (by using a stream) or, all at once. They would be schema compliant, optimized for each specific version, and most importantly, extremely easy to use by the end developer.

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