---
overlay: C# Specialization
parent_agent: Super Coder
description: "C#/.NET development patterns and best practices"
---

## C#-SPECIFIC GUIDELINES

You are working in a **C#** codebase. Apply these principles with zero exceptions.

### LINQ — Use It Everywhere
- Use LINQ for collection operations — it's more readable than manual loops
- Prefer method syntax (`.Where().Select()`) over query syntax (`from x in ...`) — follow project convention
- Use `FirstOrDefault()`, `SingleOrDefault()` — know the difference (Single throws if >1)
- Avoid `ToList()` / `ToArray()` unless you need materialization — keep queries lazy with `IEnumerable<T>`
- Use `Any()` instead of `Count() > 0` for existence checks

### Async/Await — The Right Way
- Make async methods return `Task` or `Task<T>` — never `async void` except event handlers
- Use `await` all the way — never mix `.Result` or `.Wait()` with async (deadlock risk)
- Use `ConfigureAwait(false)` in library code (not in UI/ASP.NET controller code)
- Use `CancellationToken` as the last parameter on async methods — propagate it through
- Use `ValueTask<T>` for hot-path methods that frequently complete synchronously

### Nullable Reference Types
- Enable `<Nullable>enable</Nullable>` — if the project has it, respect it fully
- Use `?` suffix for nullable: `string?` means "might be null"
- Use `!` (null-forgiving) only when you've verified non-null through logic the compiler can't see — add a comment
- Use `[NotNull]`, `[MaybeNull]`, `[NotNullWhen]` attributes for nuanced nullability
- Prefer `is not null` over `!= null` in pattern matching contexts

### Record Types & Immutability
- Use `record` types for immutable data transfer objects: `record UserDto(string Name, string Email);`
- Use `record struct` for value-type records (stack-allocated, no GC pressure)
- Use `with` expressions for non-destructive mutation: `var updated = user with { Name = "New" };`
- Use `init` properties for immutable-after-construction objects
- Use `required` keyword (C# 11+) for mandatory init properties

### Pattern Matching
- Use pattern matching in `switch` expressions — cleaner than if/else chains
- Use `is` patterns: `if (obj is string s)`, `if (value is > 0 and < 100)`
- Use `switch` expressions for exhaustive matching: `var result = status switch { ... }`
- Use property patterns: `if (user is { Name: "admin", IsActive: true })`
- Use discard `_` for cases you don't handle: `_ => throw new InvalidOperationException()`

### Entity Framework Core (if applicable)
- Use `AsNoTracking()` for read-only queries — significant performance improvement
- Use `Include()` for eager loading — avoid N+1 queries
- Use `AsSplitQuery()` for queries with multiple includes
- Keep DbContext lifetime short — scoped per request in ASP.NET
- Use migrations — never modify the database schema manually

### Naming Conventions
- `PascalCase` for classes, methods, properties, events, namespaces
- `camelCase` for local variables, parameters
- `_camelCase` for private fields (with underscore prefix)
- `I` prefix for interfaces: `IUserRepository`
- `Async` suffix for async methods: `GetUserAsync()`
- Boolean properties: `Is*`, `Has*`, `Can*`

### Testing Considerations
- Use constructor injection for testability — all dependencies through constructor
- Use interfaces for external dependencies — mockable with Moq, NSubstitute, etc.
- Follow project's test framework conventions (xUnit, NUnit, MSTest)