What .NET version to choose?

Question

I am writing public .NET class library version for our online REST service and I can't decide which version of .NET to choose.

I would like to use .NET 4.0 version but such compiled class library can't be used in .NET 2.0 version?

Maybe there is statistic how many developers use .Net 2.0 version?

Answer 1

There's little reason not to use the latest version of the framework. Not only do you get all the latest features and whistles that speed development time, but you also get to take advantage of all the bug fixes and improvements that Microsoft has done under the hood.

The only advantage of targeting earlier versions of the framework is in a vain hope that the user won't have to download and install anything in order to use your app. But that's far from foolproof, and mostly in vain. Remember that Windows is not a .NET Framework delivery channel and you can't reliably assume that the user will have any version of the .NET Framework installed. Even if you insisted on counting on it being bundled with Windows (which you shouldn't), lots of users still haven't upgraded from Windows XP. Even if you counted on it being pushed out over Windows Update, there are significant numbers of users who either don't use Windows Update, don't use Windows Update very often, or who live out in remote areas with poor/slow Internet access and can't download all of those updates.

The moral of the story is that you're going to have to provide the appropriate version of the .NET Framework with your application anyway. And the .NET 4.0 runtime is actually significantly smaller than the previous versions, so there's little reason to target them. The team has worked really hard on that, and their efforts have really paid off. Even better, as atornblad notes, most apps can target the Client Profile version of the framework which trims out some infrequently used pieces and slims things down another ~16%.

Additionally, I strongly recommend using a setup application that handles installing the required framework for the user automatically and seamlessly. Visual Studio comes with built-in support for creating setup applications, or you could use a third-party installer utility like Inno Setup. That makes using the latest version a no-brainer.

Answer 2

Everyone else seems to be recommending using the latest version, so I'll buck the trend and suggest 2.0 if you don't actually need any features from later versions... if this really is a client library and you have no control over and little idea about who is going to use it.

It really does depend on who your users are likely to be, which in turn depends on what the REST service is. If it's some sort of social media thing, then I'd say it's more likely that your clients will be in environments where they can use .NET 4. If it's something which might well be used by financial institutions or other big businesses, they may well not have the option of using .NET 4, so you should consider earlier versions. This is the approach we've taken for Noda Time where we believe the library will be useful in a wide variety of situations, and we can't predict the client requirements.

Of course, if you know all your clients and know they will all be able to use .NET 4, then go with that.

The big downsides of sticking to .NET 2.0 are that you won't be able to use LINQ internally (unless you use LINQBridge or something similar, which adds another dependency for your library) and you won't be able to (cleanly) provide extension methods. If you can usefully expose more features to the client if you use a later version, you may want to provide multiple versions of the library - but obviously that's a maintenance headache.

Another consideration is whether you ought to provide a Silverlight version - which again depends on what sort of service you're providing and what sort of users you're expecting.