Why do .NET 10 / C# 14 extension members only work in Visual Studio 2026?

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Summary

The issue of C# 14 extension members not working in JetBrains Rider or Visual Studio 2022, despite the same .NET 10 SDK being installed, is due to incomplete IDE support for the new language features. This results in the code compiling and working correctly only in Visual Studio 2026.

Root Cause

The root cause of this issue is:

  • Incomplete IDE support for C# 14 extension members in JetBrains Rider and Visual Studio 2022
  • Difference in Roslyn integration between Visual Studio 2026 and other IDEs
  • Limitation in handling new language features in JetBrains Rider and Visual Studio 2022

Why This Happens in Real Systems

This issue occurs in real systems due to:

  • Variations in IDE versions and their support for new language features
  • Differences in Roslyn integration and compiler versions used by different IDEs
  • Incomplete or inconsistent implementation of new language features in various IDEs

Real-World Impact

The real-world impact of this issue includes:

  • Inconsistent development experiences across different IDEs
  • Difficulty in adopting new language features due to limited IDE support
  • Increased development time and frustration due to compatibility issues

Example or Code

public static class MyExtensions 
{ 
    public static int WordCount(this string s) 
    { 
        return s.Split(' ', StringSplitOptions.RemoveEmptyEntries).Length; 
    } 
}

class Program 
{ 
    static void Main() 
    { 
        string text = "Hello from C# 14"; 
        Console.WriteLine(text.WordCount()); 
    } 
}

How Senior Engineers Fix It

Senior engineers fix this issue by:

  • Verifying the IDE version and its support for new language features
  • Checking the Roslyn integration and compiler version used by the IDE
  • Updating the IDE or switching to a compatible version
  • Using workarounds or alternative implementations when necessary

Why Juniors Miss It

Juniors may miss this issue due to:

  • Lack of experience with different IDEs and their versions
  • Insufficient knowledge of Roslyn integration and compiler versions
  • Inadequate understanding of new language features and their implementation
  • Failure to test the code in different environments and IDEs