csharp-best-practices
DevelopmentC#/.NET conventions for this user's projects — multi-targeting for libraries, NUnit/xUnit testing, warnings-as-errors, immutability, exception-based error handling, and dependency injection used selectively. Use when writing or reviewing C# code, .csproj/Directory.Packages.props files, or test suites in a .NET project.
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C# Best Practices
Why: Design for Change
The goal is code that looks deceptively simple — simple enough that a reader asks how it took so long to write — but is easy to change, test, and use. Anything unusual gets a comment explaining why, not what.
Compiler / runtime settings
- SDK pinned via
global.json. - Dependency versions centralized via
Directory.Packages.props(Central Package Management) rather than per-project version strings. - Compiler warnings are strict — treat as effectively warnings-as-errors. Analyzer (code-style) warnings are looser; use judgement rather than blocking on every one.
- Libraries (anything with broad external consumers, like Noda Time): multi-target the same broad TFM spread the project already targets — don't drop old TFMs casually.
- Internal tools: fine to target the latest LTS only — no need to multi-target.
Type system & modeling
Lean toward immutable types for new code. OO by default; reach for functional approaches (pure functions, expression-bodied members, LINQ pipelines) where they make the code clearer, not as a rule unto itself.
Error handling
Exceptions, in almost all cases — not Result/Either types, not error tuples. Don't introduce a Result type pattern unless explicitly asked.
Dependency injection
Use DI for web projects. Skip it for smaller tools and libraries — don't wire up a DI container where it isn't earning its keep.
External API clients
When consuming an external API, prefer an existing dedicated client library over hand-rolling HTTP calls, unless none exists or it's unsuitable.
Testing conventions
- Tests are written alongside production code, in the same commit — not strictly tests-first, not tests-after.
- Runner: NUnit or xUnit depending on the project. Never MSTest.
- Don't be dogmatic about unit testing specifically — higher-level (integration/smoke) tests often carry more value than exhaustive unit coverage. Match the project's existing test shape rather than imposing one.
- Coverage targets are project-specific: Noda Time targets ~99%; most other projects carry no coverage target. Don't impose a coverage bar that isn't already there.
Patterns to use with judgement, not by default
- Singleton: commonly overused by teams, but occasionally the right tool. Don't reject it on sight, and don't reach for it by default either.
Standard rules for every type / class / module
No fixed project-wide template (e.g. no blanket "every class must override ToString()" rule) — follow the conventions already established in the specific project being worked on.