Generators.NET

.NET compatibility

Fern-generated .NET SDKs support modern .NET versions, .NET Framework versions, and Unity.

Because these SDKs are built with modern C# features, you’ll need the following even when targeting older .NET Framework targets:

  • A modern compiler (Visual Studio 2022 or .NET SDK)
  • The appropriate .NET Framework Developer Pack or reference assemblies

Supported frameworks

Fern .NET SDKs support all officially supported .NET versions, except for net35.

FrameworkTarget Framework Moniker (TFM)
.NET 9net9.0
.NET 8net8.0
.NET Framework 4.8.1net481
.NET Framework 4.8net48
.NET Framework 4.7.2net472
.NET Framework 4.7.1net471
.NET Framework 4.7net47
.NET Framework 4.6.2net462

The C# language version is determined by your compiler, while the target framework determines which runtime and base class library APIs are available. Fern SDKs use modern C# features but compile to older framework versions.

All major IDEs support Fern-generated SDKs when targeting net462, net472, and net48 versions:

  • Visual Studio 2022 (recommended) - Works out of the box. Set <LangVersion> in your project and install the appropriate developer pack.
  • Visual Studio 2019 - Supports C# 9 natively. For newer C# versions, add the Microsoft.Net.Compilers.Toolset package.
  • Rider - Uses Roslyn. Set <LangVersion> and ensure reference assemblies are available.
  • VS Code - Works via OmniSharp and .NET SDK builds.
  • Unity - Uses Unity’s own C# compiler. See Using SDKs with Unity.

You can “bring your own compiler” with the Microsoft.Net.Compilers.Toolset package on any environment.

Use the Roslyn compiler (csc) that comes with Visual Studio 2022+ or the .NET SDK. Set your C# version via <LangVersion> to latest, preview, or a specific version (minimum 9).

Fern’s .NET SDK doesn’t support the legacy Mono compiler (mcs, gmcs) or the pre-Roslyn csc.exe compiler. Use Roslyn even when building on Mono.

Building on Mono

Use the .NET SDK (dotnet) with the Microsoft.NETFramework.ReferenceAssemblies package to supply net48 references on non-Windows. Use Roslyn via dotnet build or Mono’s MSBuild.

macOS/Linux
$dotnet build -c Release

Using SDKs with Unity

Unity controls its own C# compiler and .NET profile, which affects how you use Fern’s .NET SDK.

Unity compiles projects using Roslyn, typically supporting C# 9 (varies by Unity version). You can’t force Unity to use a newer C# compiler by changing your package because Unity controls the compiler inside the Editor.

Configure this in Unity: Edit → Project Settings → Player → Other Settings → Api Compatibility Level

  • .NET Standard 2.1 (recommended for cross-platform plugins)
  • .NET Framework 4.x (Unity’s “4.x equivalent” profile)

Unity doesn’t support NuGet packages, so you must manually download and add these assemblies to your Unity project:

AssemblyNuGet Package
Microsoft.Bcl.AsyncInterfaces10.0.0-preview.6.25358.103
OneOf3.0.271
OneOf.Extended3.0.271
System.Buffers4.6.1
System.IO.Pipelines10.0.0-preview.6.25358.103
System.Memory4.6.3
System.Runtime.CompilerServices.Unsafe6.1.2
System.Text.Encodings.Web10.0.0-preview.6.25358.103
System.Text.Json10.0.0-preview.6.25358.103
System.Threading.Tasks.Extensions4.6.3
portable.system.datetimeonly9.0.0

Project configuration examples

Use SDK-style projects where possible, as they provide modern compilers and simpler multi-targeting. If you have a classic project format, consider converting to SDK-style. The legacy projects section covers legacy setups that can’t be converted.

Building on macOS/Linux

When building for net48 on macOS/Linux, you won’t have the Windows targeting packs. Add the reference assemblies package:

YourProject.csproj
1<ItemGroup>
2  <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" PrivateAssets="all" />
3</ItemGroup>

This provides the net48 reference assemblies so Roslyn can compile for net48 on any platform. You’ll still need Mono or Wine to execute the result.

For older MSBuild/Visual Studio versions, Visual Studio 2019, or legacy packages.config setups, add a modern Roslyn toolset and target the old framework.

1

Install target packs

Install the appropriate .NET Framework Developer Pack so Visual Studio can find the reference assemblies.

2

Set language version

YourProject.csproj
1<PropertyGroup>
2<!-- Unlock modern C# -->
3<LangVersion>latest</LangVersion>
4</PropertyGroup>

Or use a specific version: 9, 10, 11, 12, or preview.

3

Add modern compiler

YourProject.csproj
1 <ItemGroup>
2 <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="x.y.z">
3     <!-- Keep it private: -->
4     <PrivateAssets>all</PrivateAssets>
5 </PackageReference>
6 </ItemGroup>

This ensures your build uses a modern csc.exe even if your IDE/MSBuild is older.

Troubleshooting

Add a small shim in your project or reference a helper package.

Add Microsoft.Net.Compilers.Toolset to the project, or move to VS 2022+.

This error occurs when using the required keyword with older Visual Studio versions. Follow the instructions at Legacy projects to add a modern compiler.

Some versions of Visual Studio may show this error in the IDE but compile the project successfully when using the package-provided compiler.