.NET 4.5 and .NET 4 Won't Coexist
Developers may have to get back to .NET app migrations. The upcoming Microsoft .NET Framework is designed as an in-place update meant to replace .NET 4, instead of the side-by-side installation model that the company used with the current release.
Microsoft released a preview of the .NET Framework 4.5 in mid September as part of the Visual Studio 11 Developer Preview. The.NET Framework 4.5 has the same version number as .NET 4 and Microsoft is working to make it backwards compatible so that it supports existing applications. (.NET 4.5 and .NET 3.5 can still be installed side by side.)
Microsoft officially introduced side-by-side installations of .NET with .NET 4. Scott Guthrie explained the changes in his blog back in August of 2009:
.NET 4.0 has a new version number for both the framework libraries and CLR engine – which means it runs completely independently from .NET 2.0, 3.0 and 3.5. What this means is that you can install .NET 4.0 on a machine that has .NET 2.0/3.0/3.5 installed, and configure some applications to run using .NET 4.0 and others to run using the older .NET versions (the IIS admin tool allows you to configure this for ASP.NET applications). This allows you to use .NET 4.0 for new applications - without having to necessarily test and upgrade all your existing ones.
Microsoft is requesting feedback from early testers on application compatibility issues with .NET 4.5. Some developers are requesting that the company at least change the version number of .NET 4.5 to prevent software deployment and debugging issues. Others want Microsoft to allow .NET 4.5 to run side by side with .NET 4 to help avoid the compatibility testing and related headaches.
Microsoft's Brandon Bray indicated that compatibility isn't the only issue in response to developers' comments on a blog written by Manish Agnihotri, a Microsoft program manager, who is responsible for "driving compatibility across the .NET Framework":
I'll work on getting a discussion going about side-by-side vs. in-place releases. There's more to consider than just compatibility. And I can assure you, the comments left here are being read and discussed amongst the teams contributing to .NET.
You can still use Visual Studio 11 to build projects that multitarget .NET 4.5, .NET 4 and .NET 3.5, according to Microsoft. Limited multitargeting support was first introduced in Visual Studio 2008 and advanced in Visual Studio 2010.
Express your thoughts on side-by-side versus in-place updates to the .NET Framework. Are you prepared to test your existing applications and upgrade them if necessary to run on the next version of the .NET Framework? Drop me a line at firstname.lastname@example.org.
Posted by Kathleen Richards on 11/01/2011 at 3:49 PM