csharp-standards

name	csharp-standards
description	C# coding standards with severity-tiered rules. Use when writing, reviewing, or generating C# code.

C# Standards

ERROR (mandatory)

• Enable nullable reference types (<Nullable>enable</Nullable>)
• Use parameterized queries — never interpolate SQL strings
• Dispose all IDisposable objects — use using statements/declarations
• Never catch Exception without re-throwing or specific handling
• Async methods must have Async suffix and return Task/ValueTask
• No hardcoded connection strings or secrets — use configuration/Key Vault

WARNING (recommended)

• Use records for immutable data transfer objects
• Prefer IReadOnlyList<T> / IReadOnlyCollection<T> for return types
• Use pattern matching over type checking + casting
• Use file-scoped namespaces (C# 10+)
• Use primary constructors where appropriate (C# 12+)
• Maximum method length: 40 lines
• Use StringComparison parameter in string comparisons

RECOMMENDATION (optional)

• Use Span<T> / Memory<T> for high-performance array operations
• Consider record struct for small immutable value types
• Use System.Text.Json source generators for AOT-compatible serialization
• Use IAsyncEnumerable<T> for streaming async sequences
• Consider Channel<T> for producer/consumer patterns

Testing

• Use xUnit, NUnit, or MSTest
• Use FluentAssertions for readable assertions
• Mock interfaces with Moq or NSubstitute — never mock concrete classes
• Use WebApplicationFactory<T> for integration tests
• Test naming: MethodName_Scenario_ExpectedResult