In this post, I use the NDepend assembly comparison feature to assess the public API compatibility between Mono 2.0 and the .NET Framework 3.5 SP1.

The assemblies considered are: mscorlib,     System,     System.Core,     System.Messaging,     System.Runtime.Remoting,     System.Runtime.Serialization.Formatters.Soap,     System.Security,     System.ServiceProcess,     System.Transactions,     System.Web,     System.Web.Services,     System.Windows.Forms,     System.Xml,     System.Xml.Linq,     System.Configuration,     System.Configuration.Install,     System.Data.DataSetExtensions,     System.Data,     System.Data.Linq,     System.Data.OracleClient,     System.Design,     System.DirectoryServices,     System.Drawing.Design,     System.Drawing,     System.EnterpriseServices,     System.Management

We consider .NET Framework bits as the newer build and the Mono ones as the older build. Thus the following CQL Query lists public types of the .NET Framework not supported by Mono:

SELECT TYPES WHERE IsPublic AND WasAdded

The result is 1553 public types not supported, to compare to 5720 public types supported. On the following metric view, you can see these types in blue. Each rectangle represents an assembly, namespace, type or method and the size of the rectangle is proportional  to the underlying number of IL instructions.

With the following CQL query it is easy to pinpoint that amongst not supported types, 499 are wrapper of native win32 methods. We rely on the fact that such wrapper types are nested in outer types named NativeMethods.

SELECT TYPES WHERE IsPublic AND WasAdded AND !NameLike "NativeMethods+"

The list of the 1054 types not supported and not win32 wrappers is available here. This list includes:

• a few Windows.Forms public implementation details,
• the namespace System.Deployment.Internal.Isolation.Store,
• the namespace System.Web.UI.WebControls.WebParts,
• some ASP.NET/System.Web details like in Configuration, Security, Hosting, Caching, Management,
• some System.Security.Policy and Permissions types,
• the namespace System.Security.AccessControl,
• some CLR related public types like InsufficientMemoryException, MTAThreadAttribute, GCNotificationStatus
• some System.Runtime.Remoting and Serialization types and the namespace System.Runtime.Remoting.Metadata.W3cXsd2001
• obviously, many of the System.Runtime.InteropServices‘s types
• a few types from System.Runtime.CompilerServices, System.Reflection, System.Globalization, System.IO and System.Threading
• most of System.Diagnostics.SymbolStore’s types
• System.Web.UI.Design.WebControls‘s designer and editor (they muight be in a non-referenced assemblies ?)
• some System.Data, System.Data.SqlTypes and Microsoft.SqlServer’s types
• a few System.Xml.Serialization.Configuration’s types
• several namespaces of the assembly System.Core.dll, including System.Diagnostics.*, System.IO.*, System.Security.*, System.Threading.*, System.Management.Instrumentation.*
• most of System.DirectoryServices.dll’s types
• a few System.Transactions and System.Messaging’s types

On the other hand Mono introduces 77 new public types all listed here. This list was obtained with the CQL query:

SELECT TYPES WHERE IsPublic AND WasRemoved

Most of them look like implementation details that might be turned to internal, or that might be useful for some advanced pure-Mono scenarios.

Concerning dependencies between assemblies, the following matrix shows a few changes.

• Cells with a red tick with a + means dependency in the .NET Fx absent in Mono,
• Cells with a red tick with a - means dependency in Mono absent in the .NET Fx,
• Cells with a red tick means coupling between 2 assemblies changed between Mono and the .NET Fx,

Finally I noticed that Mono is much more lightweight in terms of IL instructions: 1 629 065 for Mono and 3 591 830 for the .NET Fx. I have no explanation for this. The missing types cannot explain such a difference (as we can see on the metric view above, displayed with the #IL instructions metric). Maybe it is due to some Mono C# compiler special behavior and optimization?