Uwe Keim Uwe Keim - 1 month ago 41
ASP.NET (C#) Question

How to use C# 6 with Web Site project type?

Updated an existing Web Site project type Visual Studio 2015, I changed the Framework to 4.6.

I then expected to have all those new features available in my code behind files.

Unfortunately I'm getting errors like:


Error CS8026: Feature 'expression-bodied property' is not available in C# 5. Please use language version 6 or greater.


or e.g.:


Error CS8026: Feature 'interpolated strings' is not available in C# 5. Please use language version 6 or greater.


I did a quick Google check and found a guy posting some comments in a blog posting of ScottGu (search for "8026" on the page).

Since I do not understand his solution, plus I want to have the solution more visible, I've created this SO posting.

My question:

How can I have a Visual Studio 2015 project of type Web Site (i.e. not Web Application) to recognize C# 6 features?

Answer

I've tested this with MVC 5 (tested 5.2.3), your mileage may vary with other web frameworks, but you just need to add the roslyn code dom Nuget package

CodeDOM Providers for .NET Compiler...

Replacement CodeDOM providers that use the new .NET Compiler Platform ("Roslyn") compiler as a service APIs. This provides support for new language features in systems using CodeDOM (e.g. ASP.NET runtime compilation) as well as improving the compilation performance of these systems.

PM> Install-Package Microsoft.CodeDom.Providers.DotNetCompilerPlatform

https://www.nuget.org/packages/Microsoft.CodeDom.Providers.DotNetCompilerPlatform/

The nuget package should add the dlls and add the following to your web.config.

  <system.codedom>
    <compilers>
      <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701" />
      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" />
    </compilers>
  </system.codedom>

If it's still missing. Try adding yourself.