csharp-rules

C#/.NET Rules

These rules come from app/rules/csharp/ in ai-toolkit. They cover the project's standards for coding style, frameworks, patterns, security, and testing in C#/.NET. Apply them when writing or reviewing C#/.NET code.

C# Coding Style

Naming

• PascalCase: classes, structs, enums, interfaces, methods, properties, events.
• camelCase: local variables, parameters, private fields.
• Prefix interfaces with I: IUserRepository, IDisposable.
• Prefix private fields with _: private readonly ILogger _logger;.
• UPPER_SNAKE: not conventional in C#. Use PascalCase for constants.

Nullable Reference Types

• Enable <Nullable>enable</Nullable> in all projects.
• Use string? only when null is semantically meaningful.
• Use ! (null-forgiving) operator sparingly -- only when compiler cannot infer.
• Use ?? (null-coalescing) and ?. (null-conditional) for safe navigation.
• Use required modifier (C# 11) on properties that must be set at initialization.

Records and Types

• Use record for immutable value objects and DTOs.
• Use record struct for small, stack-allocated value types.
• Use init properties for immutable-after-construction objects.
• Use with expressions for non-destructive mutation of records.
• Use primary constructors (C# 12) for concise class definitions.

Pattern Matching

• Use is pattern for type checks: if (obj is string s).
• Use switch expressions for exhaustive matching over enums/types.
• Use property patterns: user is { Age: > 18, Role: "admin" }.
• Use relational patterns: size is > 0 and < 100.
• Use list patterns (C# 11): numbers is [1, 2, .., var last].

Async/Await

• Suffix async methods with Async: GetUserAsync().
• Return Task<T> or ValueTask<T>, never void (except event handlers).
• Use await with ConfigureAwait(false) in library code.
• Use CancellationToken parameters in all async public APIs.
• Prefer ValueTask<T> when synchronous completion is common.

File Organization

• One type per file. File name matches type name.
• Use file-scoped namespaces (C# 10): namespace MyApp.Services;.
• Order members: fields, constructors, properties, public methods, private methods.
• Use global using directives in a single GlobalUsings.cs file.