.NET 4.5 in-place upgrade might confuse you and your users

I learned something new today, something I strive to do everyday. I learned that the new .NET 4.5 Framework doesn’t just install side by side with 4.0 but it actually “upgrades” it for you. This doesn’t sound terrible, until you realize that if you are developing an application for 4.0 (many of need to as we support XP clients, which 4.5 won’t run on).

Why the issue, well one is that you run you application and you may not get the quirks you would on a machine with just 4.0. You get the bug fixes that were done for 4.5. Why is this bad? Well, you can’t reproduce the issues your customers face, and worse you won’t see them in development. Hence, you first learn about the issue after it hits your customers. No bueno!.

The issue I am facing is more insidious. I use reflections to reach inside the bowels of the framework to do things that they won’t expose to me publicly. Sealed classes, private initializers, etc. Well, they can rename these things since they aren’t public. You see where I am going. In 4.5, my method isn’t there anymore.

So, user installs 4.5, boom goes the app. Yeah, could have happened with any bug fix, sp, or update. I just didn’t expect a new framework edition to crumble the empire.

Well, just watch out and test your apps on both 4.0 and 4.5 systems. Even if, especially if, you are writing targeted 4.0 applications.

Happy Coding!

More details I read about at Hanselman’s blog.

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