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I was working on a series of dialogs that required validation, and since there's a funky validation setup in place, I thought I might build up a nice extension library.  Noting that ASP.NET validation is far beyond Windows Forms, I thought it might also be a good opportunity to use extension methods.

Sadly, extension methods aren't supported by the C# 2.0 compiler (which I was using, part of Visual Studio 2005), nor are they supported by the .NET Framework 2.0.  So, I wouldn't get IntelliSense support, and it wouldn't build in VS 2005.  But I was curious, and since 2008 supports targeting the 2.0 framework, I thought I'd give it a shot.

So I cranked open 2008 and created a quick test project.  Building out the method: 

   1:  public static class ExtensionMethods
   2:  {
   3:      public static void ValidateMe(this Form form)
   4:      {
   5:          form.ValidateChildren(ValidationConstraints.Enabled);
   6:      }
   7:  }

I get a compiler error:

error CS1110: Cannot define a new extension method because the compiler required type 'System.Runtime.CompilerServices.ExtensionAttribute' cannot be found. Are you missing a reference to System.Core.dll?

So it appeared I would need to link to the 3.5 libraries... or would I? 

   1:  namespace System.Runtime.CompilerServices
   2:  {
   3:      [AttributeUsage(AttributeTargets.Method)]
   4:      public sealed class ExtensionAttribute : Attribute
   5:      {
   6:          public ExtensionAttribute() { }
   7:      }
   8:  }

Lo and behold, it compiled correctly.  Then it worked correctly!


(Note: I wouldn't really make a library with a function called "ValidateMe".  Never!)

posted on Thursday, December 20, 2007 2:31 PM


# re: Using Extension Methods in .NET 2.0 with Visual Studio 2008 12/21/2007 1:58 AM Daniel Moth
You are about 7 months late discovering this (see my blog) ;-)

Just wanted to make a note that the product teams are not supporting this. Also note that for the other language features you really need SP1 and not RTM of v2.0 on the deployment machine.

# re: Using Extension Methods in .NET 2.0 with Visual Studio 2008 8/26/2010 11:51 PM Rafael
Thanks! it really help

# re: Using Extension Methods in .NET 2.0 with Visual Studio 2008 2/1/2012 1:21 PM zency
thx bro ;)

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