everything-claude-code/rules/csharp/coding-style.md

---
paths:
  - "**/*.cs"
  - "**/*.csx"
---
# C# Coding Style

> This file extends [common/coding-style.md](../common/coding-style.md) with C#-specific content.

## Standards

- Follow current .NET conventions and enable nullable reference types
- Prefer explicit access modifiers on public and internal APIs
- Keep files aligned with the primary type they define

## Types and Models

- Prefer `record` or `record struct` for immutable value-like models
- Use `class` for entities or types with identity and lifecycle
- Use `interface` for service boundaries and abstractions
- Avoid `dynamic` in application code; prefer generics or explicit models

```csharp
public sealed record UserDto(Guid Id, string Email);

public interface IUserRepository
{
    Task<UserDto?> FindByIdAsync(Guid id, CancellationToken cancellationToken);
}
```

## Immutability

- Prefer `init` setters, constructor parameters, and immutable collections for shared state
- Do not mutate input models in-place when producing updated state

```csharp
public sealed record UserProfile(string Name, string Email);

public static UserProfile Rename(UserProfile profile, string name) =>
    profile with { Name = name };
```

## Async and Error Handling

- Prefer `async`/`await` over blocking calls like `.Result` or `.Wait()`
- Pass `CancellationToken` through public async APIs
- Throw specific exceptions and log with structured properties

```csharp
public async Task<Order> LoadOrderAsync(
    Guid orderId,
    CancellationToken cancellationToken)
{
    try
    {
        return await repository.FindAsync(orderId, cancellationToken)
            ?? throw new InvalidOperationException($"Order {orderId} was not found.");
    }
    catch (Exception ex)
    {
        logger.LogError(ex, "Failed to load order {OrderId}", orderId);
        throw;
    }
}
```

## Formatting

- Use `dotnet format` for formatting and analyzer fixes
- Keep `using` directives organized and remove unused imports
- Prefer expression-bodied members only when they stay readable