Modern C# for .NET

Trigger On

• the repo wants more modern idiomatic C# code
• a change depends on language-version compatibility
• the team is upgrading or reviewing C# feature usage across versions
• you need to know whether a C# 13 or C# 14 feature is safe to use

Workflow

1. Detect the real language ceiling from the repo's target framework and explicit LangVersion.
2. Prefer stable features that the current repo actually supports.
3. Use modern syntax when it reduces ceremony, improves correctness, or makes invariants clearer.
4. Do not mass-rewrite a codebase into newer syntax unless the repo wants that churn.
5. Treat preview features as opt-in only. Never assume preview because the current machine has a newer SDK.
6. Pay special attention to C# 13 and C# 14:

- C# 13 is the stable language for .NET 9 - C# 14 is the stable language for .NET 10

1. When feature selection changes architecture, style rules, or generated-code patterns, coordinate with:

- dotnet - analyzer-config - architecture

1. After feature-driven refactors, run the repo's .NET quality pass through dotnet.

Deliver

• modern C# code that fits the repo's real language version
• fewer obsolete patterns when a newer stable feature is clearer
• no accidental preview or unsupported-language drift

Validate

• the chosen syntax is supported by the repo's TFM and LangVersion
• the feature improves clarity, correctness, or maintainability
• preview-only features are used only when the repo explicitly opted in
• style and analyzer rules still agree with the new syntax

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