> This page is for SDK, version Legacy. > For other versions, use one of these documentation indexes: > - Current (default): https://buildwithfern.com/learn/sdks/current/llms.txt > - Legacy: https://buildwithfern.com/learn/sdks/legacy/llms.txt > For clean Markdown content of this page, append .md to this URL. For the complete documentation index, see https://buildwithfern.com/learn/llms.txt. # .NET compatibility > Learn about supported .NET Framework versions (net462, net472, net48) and Unity compatibility for Fern-generated SDKs. > **You're viewing the legacy SDK docs** > > These pages cover SDK generation configured with `generators.yml`. New projects use `sdk-config.yml`, so see [the Current version of this page](/learn/sdks/generators/csharp/version-compatibility) for up-to-date guidance. To move an existing project, follow the [SDK Config migration guide](/learn/sdks/legacy/generators/migration-guides/sdk-config), which walks through `fern sdk migrate`, and review the [`sdk-config.yml` reference](/learn/sdks/reference/sdk-config). 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](https://dotnet.microsoft.com/en-us/platform/support/policy/dotnet-framework), except for net35. | Framework | Target Framework Moniker (TFM) | | -------------------- | ------------------------------ | | .NET 9 | net9.0 | | .NET 8 | net8.0 | | .NET Framework 4.8.1 | net481 | | .NET Framework 4.8 | net48 | | .NET Framework 4.7.2 | net472 | | .NET Framework 4.7.1 | net471 | | .NET Framework 4.7 | net47 | | .NET Framework 4.6.2 | net462 | > **Note** > > 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. #### IDE compatibility All major IDEs support Fern-generated SDKs when targeting `net462`, `net472`, and `net48` versions: * **Visual Studio 2022** (recommended) - Works out of the box. Set `` in your project and install the appropriate [developer pack](#developer-packs). * **Visual Studio 2019** - Supports C# 9 natively. For newer C# versions, add the `Microsoft.Net.Compilers.Toolset` package. * **Rider** - Uses Roslyn. Set `` 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](#using-sdks-with-unity). > **Info** > > You can "bring your own compiler" with the `Microsoft.Net.Compilers.Toolset` package on any environment. #### Compiler compatibility Use the **Roslyn compiler** (`csc`) that comes with Visual Studio 2022+ or the .NET SDK. Set your C# version via `` 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. > > ```bash title="macOS/Linux" > dotnet build -c Release > ``` #### Developer packs * [.NET Framework 4.6.2 Developer Pack](https://dotnet.microsoft.com/en-us/download/dotnet-framework/net462) * [.NET Framework 4.7.2 Developer Pack](https://dotnet.microsoft.com/en-us/download/dotnet-framework/net472) * [.NET Framework 4.8 Developer Pack](https://dotnet.microsoft.com/en-us/download/dotnet-framework/net48) ## Using SDKs with Unity Unity controls its own C# compiler and .NET profile, which affects how you use Fern's .NET SDK. #### C# language version 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. #### API compatibility level 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) #### Required assemblies Unity doesn't support NuGet packages, so you must manually download and add these assemblies to your Unity project: | Assembly | NuGet Package | | -------------------------------------- | --------------------------------------------------------------------------------------------------------------------- | | Microsoft.Bcl.AsyncInterfaces | [10.0.0-preview.6.25358.103](https://www.nuget.org/packages/Microsoft.Bcl.AsyncInterfaces/10.0.0-preview.6.25358.103) | | OneOf | [3.0.271](https://www.nuget.org/packages/OneOf/3.0.271) | | OneOf.Extended | [3.0.271](https://www.nuget.org/packages/OneOf.Extended/3.0.271) | | System.Buffers | [4.6.1](https://www.nuget.org/packages/System.Buffers/4.6.1) | | System.IO.Pipelines | [10.0.0-preview.6.25358.103](https://www.nuget.org/packages/System.IO.Pipelines/10.0.0-preview.6.25358.103) | | System.Memory | [4.6.3](https://www.nuget.org/packages/System.Memory/4.6.3) | | System.Runtime.CompilerServices.Unsafe | [6.1.2](https://www.nuget.org/packages/System.Runtime.CompilerServices.Unsafe/6.1.2) | | System.Text.Encodings.Web | [10.0.0-preview.6.25358.103](https://www.nuget.org/packages/System.Text.Encodings.Web/10.0.0-preview.6.25358.103) | | System.Text.Json | [10.0.0-preview.6.25358.103](https://www.nuget.org/packages/System.Text.Json/10.0.0-preview.6.25358.103) | | System.Threading.Tasks.Extensions | [4.6.3](https://www.nuget.org/packages/System.Threading.Tasks.Extensions/4.6.3) | | portable.system.datetimeonly | [9.0.0](https://www.nuget.org/packages/portable.system.datetimeonly/9.0.0) | ## 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](#legacy-projects) 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: > > ```xml title="YourProject.csproj" > > > > ``` > > 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. #### SDK-style projects (recommended) Targeting `net48` with modern C# #### Configure your project > **Prerequisite (Windows)** > > Install the [.NET Framework 4.8 Developer Pack](#developer-packs) so the `net48` reference assemblies are available to the compiler. **`YourProject.csproj`** ```xml title="YourProject.csproj" net48 latest enable ``` #### Build your project ```bash dotnet build -c Release ``` #### Multi-target (optional) To support multiple frameworks, use ``: **`YourProject.csproj`** ```xml title="YourProject.csproj" net48;net8.0 ``` #### Legacy projects For older MSBuild/Visual Studio versions, Visual Studio 2019, or legacy `packages.config` setups, add a modern Roslyn toolset and target the old framework. #### Install target packs Install the appropriate [.NET Framework Developer Pack](#developer-packs) so Visual Studio can find the reference assemblies. #### Set language version **`YourProject.csproj`** ```xml title="YourProject.csproj" latest ``` Or use a specific version: `9`, `10`, `11`, `12`, or `preview`. #### Add modern compiler **`YourProject.csproj`** ```xml title="YourProject.csproj" all ``` This ensures your build uses a modern `csc.exe` even if your IDE/MSBuild is older. ## Troubleshooting #### Type or namespace IsExternalInit not found Add a small shim in your project or reference a helper package. #### Reference assemblies for .NETFramework,Version=v4.8 were not found * Windows: install the [.NET Framework 4.8 Developer Pack](#developer-packs). * Cross-platform/CI: add `Microsoft.NETFramework.ReferenceAssemblies` to the project (as `PrivateAssets=all`). #### VS 2019 can't parse newer syntax Add `Microsoft.Net.Compilers.Toolset` to the project, or move to VS 2022+. #### CS0619: Constructors of types with required members are not supported This error occurs when using the `required` keyword with older Visual Studio versions. Follow the instructions at [Legacy projects](#legacy-projects) to add a modern compiler. > **Note** > > Some versions of Visual Studio may show this error in the IDE but compile the project successfully when using the package-provided compiler.