Question

Under Visual Studio 2008
Can I create an Extension Method to work under a .NET Framework 2.0 project?

Answer 1

There is an ugly hack that gets Extension methods working in .Net 2.0; but it would better just to upgrade your framework to 3.5.

Alternate Sources: 1, 2.

In short (from link #2): Extension methods are just normal static methods tagged with the [Extension] attribute. This attribute is actually just added by the compiler behind the scenes. In .NET 3.5, it lives in System.Core, so just define your own attribute like this:

namespace System.Runtime.CompilerServices
{
  [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = false)]
  public class ExtensionAttribute : Attribute
  {
  }
}