Breaking Changes in .Net 4.0

Breaking changes in .NET 4.0

The languages documentation team publishes separate documents for C# and VB breaking changes:

VB: http://msdn.microsoft.com/en-us/library/cc714070%28VS.100%29.aspx

C#: http://msdn.microsoft.com/en-us/library/ee855831%28VS.100%29.aspx

I wrote the C# one and included covariance and contravariance breaking changes mentioned by Eric Lippert, and events changes discussed by Chris Burrows. There are also some breaking changes around optional parameters, embedded interop types, and method group type inference.

Update:

One more useful document (from .NET documentation team): http://msdn.microsoft.com/en-us/library/ee941656%28VS.100%29.aspx

Will I have any issues if I upgrade from .NET 4.0 to 4.5

1. Once 4.5 is installed then everything that used 4.0 before will use 4.5.
2. There are a handful of compatibility issues that exist. Elegant Code describes the issue we ran into at work when upgrading to 4.5
3. You have to uninstall 4.5 and then re install 4.0 in order to back out 4.5.

Migrating .NET 4.0 application and deploying in Windows Server 2016

I have made this move from Windows Server 2008 R2 to Windows Server 2016 and it did not need to upgrade any web application. They run just fine.

Some issues that you may have are:

• As years pass by, you always make small changes on IIS, add some MIME types, change some permissions... change some ISAPI filters - stuff like that may show you some errors at first.
• New Permissions on the servers web site directory and on the databases.
• Maybe some extra ISAPI filter that is not run anymore on the new IIS

Differences between .NET 4.0 and .NET 4.5 in High level in .NET

What is new in .NET Framework 4.5 & What's new and expected in .NET Framework 4.5:

• Support for Windows Runtime
• Support for Metro Style Applications
• Support for Async Programming
• Garbage Collector Improvements
• Faster ASP.NET Startup
• Better Data Access Support
• WebSockets Support
• Workflow Support - BCL Support

differences in ASP.NET in these frameworks

Compare What's New in ASP.NET 4 and Visual Web Developer and What's New in ASP.NET 4.5 and Visual Studio 11 Beta:

Asp.net 4.0

• Web.config File Refactoring
• Extensible Output Caching
• Auto-Start Web Applications
• Permanently Redirecting a Page
• Shrinking Session State
• Expanding the Range of Allowable URLs
• Extensible Request Validation
• Object Caching and Object Caching Extensibility
• Extensible HTML, URL, and HTTP Header Encoding
• Performance Monitoring for Individual Applications in a Single Worker Process
• Multi-Targeting
• etc

And for Asp.net 4.5 there is also a long list of improvements:

• Asynchronously Reading and Writing HTTP Requests and Responses
• Improvements to HttpRequest handling
• Asynchronously flushing a response
• Support for await and Task-Based Asynchronous Modules and Handlers

differences in C# also in these frameworks

Go Through C# 4.0 - New C# Features in the .NET Framework and What's New for Visual C# in Visual Studio 11 Beta.

Edit:
The languages documentation for C# and VB breaking changes:

VB: Visual Basic Breaking Changes in Visual Studio 2012

C#: Visual C# Breaking Changes in Visual Studio 2012

Hope this help you get what are you looking for..

Upgrade checklist for latest .NET and ASP.NET Core (v6)

General checklist for any version

1. Pre-upgrade

• If you're upgrading a non-trivial production system, ensure you have a few days to spare
• Make a list of all your third-party libraries (nugets), and visit their repos. Ensure each one supports the latest framework version - if not, then you 1) cannot upgrade yet, or 2) must find replacements for those not yet compatible with the latest framework.

2. Upgrade

• Checkout new git branch
• Run all tests: important to take a baseline before upgrading, to be able to compare before/after. Take note of failing tests, if any (so they can be ignored later).
• Review release notes
  
  • General: v6
  • .NET: v5, v6
  • C#: v9, v10
  • ASP.NET Core: v5, v6
  • EF Core: v5, v6
• Review official migration guides
  
  • General: 3.1 -> 5.0, 5.0 -> 6.0
  • Samples: 3.1/5.0 -> 6.0
• Review breaking changes
  
  • C#: overview, v9, v10
  • ASP.NET Core: 3.1 -> 5.0, 5.0 -> 6.0
  • EF Core: v5, v6
• Update dependencies (in Directory.Build.props or MyProject.csproj)
  
  • Update SDK if necessary
  • Update framework: <TargetFramework>net6.0</TargetFramework>
  • Update language version (if necessary): <LangVersion>10.0</LangVersion>
  • Update Microsoft packages named Microsoft.AspNetCore.* and Microsoft.Extensions.*
  • Update other dependencies, only if necessary (to reduce this migration's complexity). Update libraries which have been updated for the new framework version, as well as those that must be updated, e.g. non-Microsoft database providers.
  • Update relevant dotnet tools, if necessary (in dotnet-tools.json, or those installed globally)
• Handle breaking changes
  
  • Fix broken code
  • Fix broken tests; ignore failing tests which were already broken before the migration (fix them later)
• Remove obsolete workarounds. Find those workarounds that are no longer necessary due to changes/fixes in the latest framework. Typically those you've (hopefully) noted with something like // workaround: will be fixed in v6.
• Add new Roslyn analysers to .editorconfig: v5, v6
• Rerun tests, and compare to baseline
• Update documentation
  
  • Update relevant project documentation
  • Search for and update version-specific links, if necessary, e.g. links to learn.microsoft.com often have a version number like &view=aspnetcore-5.0 when there could be behaviour changes between versions
• Commit the git branch

3. Post-upgrade

• Adopt new features, if necessary and/or desired. Most new framework features are optional, so only adopt them if you really want them.
• Perform tasks necessary to satisfy your continuous integration system, if appropriate.

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Checklist for v6

3. Post-upgrade

• Adopt major new features, optional
  
  • Refactor for global using directives
  • Refactor for file-scoped namespaces
    
    • Easiest to do with dotnet format: example
    • Also add new analysers to .editorconfig: csharp_style_namespace_declarations = file_scoped:suggestion and dotnet_diagnostic.IDE0161.severity = warning
  • Refactor for new minimal hosting model, by merging Program.cs and Startup.cs
  • Refactor for minimal APIs

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