C# 14 Extension Members: Enhancing Polyfill Libraries

C# 14 introduces extension members, expanding beyond instance methods to include extension properties and static methods. This enhancement enables polyfill libraries to backport modern .NET APIs to older framework versions more comprehensively. Previously, polyfill libraries could only provide instance methods through extension methods, but now they can implement static methods like ArgumentNullException.ThrowIfNull for older .NET versions. The Meziantou.Polyfill package demonstrates this capability by using source generators to automatically add over 350 polyfilled types, methods, and properties based on target framework, reducing the need for conditional compilation directives.