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I came across an issue that makes me think there is bug in the 3.0 framework. When I try to use extension methods I get the following error:
Missing compiler required member 'System.Runtime.CompilerServices.ExtensionAttribute..ctor' When using this simple code:
public static class StringUtils { static void TestExtension(this String targetString) { } } The only way to make this compile error go away is to add the following code:
namespace System.Runtime.CompilerServices { public class ExtensionAttribute : Attribute { } } It's been a few months since I have used extensions methods, but I'm pretty sure I didn't have to do this. Has anyone else come across this issue?
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Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are static methods, but they're called as if they were instance methods on the extended type.
Extension methods are an excellent addition to the C# language. They enable us to write nicer, more readable code. They allow for more functionally styled programming, which is very much needed in an object-oriented language. They also should be used with care.
An extension method must be a static method. An extension method must be inside a static class -- the class can have any name. The parameter in an extension method should always have the "this" keyword preceding the type on which the method needs to be called.
Extension methods can also access private static members of their static utility class. Even though this is tagged as C#, this applies to any of the . NET languages which provide support for extension methods.
I have the exact same problem. The error System.Runtime.CompilerServices.ExtensionAttribute..ctor is rather cryptic, and could mean a number of different things.
However, for me It boiled down to the fact that I'm using Newtonsoft.Json.Net. I removed the reference to the file Newtonsoft.Json.Net20.dll, and the re-added it. After this my solution builds again.
The strangest thing is that when I tried to find out what was different after this procedure by using Subversion Diff, nothing appears to have changed.
So I really don't know what removing and re-adding this reference really does, but it does fix my build issue with this particular error message mentioned by the asker.
For those that come across this again, as the comenters pointed out, the proper way to fix this is to Download Json.Net's ZIP, and there should be a 3.5 version, re-reference 3.5 every where you are using Json.Net and delete the old reference, as it is likely referencing an assembly that was built for older versions of .net.
Charlie Flowers points out that the DLL NewtonSoft labels as being for 3.5 is actually not going to work with 3.5. You have to use the DLL they label as being for .net 2.0
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I just ran into this problem myself. In my case, it was because I converted a VS 2005/.Net 2.0 project to a VS 2008/.Net 3.5 project. The conversion tool kept references to System.Core 2.0, and I couldn't find an easy way to change the references to System.Core 3.5.
I ended up re-creating the project in VS 2008 from scratch, and it was created with proper references to System.Core 3.5
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