How to enable C# 9.0-preview

问题

I have downloaded and installed v5.0.0-preview.5. My project is targeting net5.0 but C# 9.0 is not working. How can I enable C# 9.0?

回答1:

According to this page in the documentation you need to edit your *.csproj to set the <LangVersion> to preview.

Also mentioned in the blog-post about the preview-release, but not the above documentation page, is that you need to update your project's targetFramework property too to net5.0 _{(this is because the C# design team decided to restrict entire C# language versions to minimum BCL versions, unlike previously where you could use C# 7 with even .NET Framework 2.0 provided you reimplemented your own missing BCL types like ValueTuple and ExtensionAttribute).}

So your *.csproj file should look like this:

<Project>
 <PropertyGroup>
   <LangVersion>preview</LangVersion>
   <TargetFramework>net5.0</TargetFramework>
 </PropertyGroup>
</Project>

回答2:

Firstly Download .NET 5 and then install Visual Studio Preview Edition. You will now have access to the latest features of C# 9. Also make sure that you project file includes the following.

 <PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net5.0</TargetFramework>
<LangVersion>preview</LangVersion>

来源：https://stackoverflow.com/questions/62398572/how-to-enable-c-sharp-9-0-preview