Update: as Daniel Moth has pointed out in the comments, it is possible to use extension methods in Orcas projects targeting .NET 2.0 by introducing your own System.Runtime.CompilerServices.ExtensionAttribute class. See Daniel’s blog post for more details.
One of the neat things about Visual Studio 2008 is that you can target .NET 2.0, 3.0 and 3.5. I’m hoping to start using it professionally shortly after it’s released – assuming stability and performance aren’t an issue, of course. The great thing is that some of the C# 3 features don’t require any framework support at all (and none of them require CLR support, as far as I’m aware). So, I’ll be able to use anonymous types, local variable type inference, object initializers, collection initializers and automatic properties. Sure, there’s no LINQ, but I can take that hit.
But what about extension methods? As far as I can figure out, they only require one feature from the framework: an attribute to decorate a method to say that it’s an extension method. If we could provide that as a compile-time option, we could use extension methods in .NET 2.0 projects, assuming I haven’t forgotten something important.
Now, I know there’s a lot of controversy about whether extension methods are really a good idea in the first place – but I for one would welcome the opportunity to use them in .NET 2.0 projects. My wild guess is that I won’t be able to use .NET 3.5 until mid-2009, and that a lot of other developers will be in the same boat. I’m sure the transition from 2.0 to 3.5 will be faster than 1.1 to 2.0 – and I doubt that many people will target 3.0 at all – but it’ll still be far from instantaneous.
The obvious downside of this would be everyone creating their own attributes and using them throughout their projects. However, it wouldn’t take long to remove them when the project moved on to .NET 3.5 – delete the attribute and remove the compiler option, then fix the compilation errors.
It’s too late to suggest this for the Orcas timeframe, really, which is a shame. I wish I’d thought of it earlier – although I suspect it’s been suggested before, so it probably wouldn’t make any odds. Anyway, what do you all think?