Polyfill

Source only package that exposes newer .NET and C# features to older runtimes.

The package targets netstandard2.0 and is designed to support the following runtimes.

• net461, net462, net47, net471, net472, net48, net481
• netcoreapp2.0, netcoreapp2.1, netcoreapp3.0, netcoreapp3.1
• net5.0, net6.0, net7.0, net8.0, net9.0, net10.0, net11.0
• uap10

Usage

After installing the NuGet package, polyfilled types and extension methods are available automatically. No extra using statements are needed beyond what the newer API requires.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <LangVersion>latest</LangVersion>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Polyfill" Version="*" PrivateAssets="all" />
  </ItemGroup>
</Project>

Key Features

• Source only — compiles directly into the consuming project, no runtime dependency.
• 881 polyfilled APIs across attributes, extension methods, and static helpers.
• Conditional compilation — only the APIs missing from the target framework are included.
• Optional feature groups — Ensure, Guard, Nullability, ArgumentExceptions, StringInterpolation.

Documentation

See the full documentation on GitHub for the complete API list, configuration options, and troubleshooting.

A compiled library variant is also available: PolyfillLib

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