polyfill-dotnet-api

To use modern .NET BCL APIs in .NET Framework 4.72, you need to apply a polyfill that restores API parity by selecting the correct source like Microsoft packages, PolySharp, or hand-rolled code. This identifies the exact missing API surface and implements the appropriate compatibility layer.

The best way to polyfill missing .NET APIs is to evaluate availability and select the optimal source, choosing between Microsoft-shipped packages, PolySharp source generators, or hand-rolled polyfills. This approach ensures behavior parity with modern BCL surfaces while capturing recurring design gotchas.

Choosing between PolySharp and Microsoft packages depends on availability and your project's source-selection rules. PolySharp provides source-generated polyfills, while Microsoft packages offer shipped binaries, and hand-rolled polyfills handle custom edge cases to ensure full behavior parity.

Polyfilling .NET BCL APIs ensures behavior parity with modern frameworks by matching the modern API surface including edge cases and allocation strategies. It updates tests, documentation, and compatibility notes to accurately reflect the selected polyfill approach.

You need a hand-rolled polyfill when Microsoft packages or PolySharp source generation cannot adequately cover the required API surface or handle specific edge cases. It restores downlevel usage by manually implementing the missing BCL API behavior for net472.