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Error when using extension methods in C#

Asked 2008-10-15T17:29:07.770
59

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?

c# .net-3.5 extension-methods
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2 Answers

18

in VS, click Project (next to File,Edit,View), select Properties

then in Application tab (you'll notice you're already in 3.5), select the Target Framework to 2.0, then compile (it will error). then put it back again to 3.5, then compile again, the error will disappear

i think it is just a small glitch in Visual Studio, just fool the IDE :-)

answered 2008-12-20T17:34:28.087
0

Try: Project, Add Reference, find System Core 3.5.0.0 in the list, and OK to add it.

answered 2008-12-25T17:52:55.003

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