Pattern Enforcement

Ensure code follows established project patterns and conventions.

Discovery Phase

Before implementing, identify project patterns:

1. Check CLAUDE.md for documented conventions
2. Search for similar code to understand existing patterns
3. Look for pattern indicators:
   • Factory functions
   • Registry patterns
   • Repository pattern for data access
   • Adapter pattern for integrations
   • Strategy pattern for variants

Common Patterns to Enforce

Structural Patterns

Registry Pattern:

Language	Idiomatic Form
TypeScript	const registry = new Map<string, Handler>(); registry.set('key', impl);
Go	var registry = map[string]Handler{} with sync.RWMutex for concurrent access
Rust	lazy_static! { static ref REGISTRY: Mutex<HashMap<String, Box<dyn Handler>>> = ...; }
C#	services.AddSingleton<IRegistry, Registry>(); via DI container
Java	@Component with Map<String, Handler> injected via Spring
Elixir	Registry module or ETS-backed lookup

Factory Pattern:

Language	Idiomatic Form
TypeScript	function createUser(data: UserInput): User { ... }
Go	func NewUser(data UserInput) (*User, error) { ... }
Rust	impl User { pub fn new(data: UserInput) -> Result<Self> { ... } }
C#	public static User Create(UserInput data) { ... }
Java	public static User create(UserInput data) { ... }
Swift	static func create(from data: UserInput) -> User { ... }
Kotlin	fun createUser(data: UserInput): User { ... } (top-level or companion object)
Elixir	def new(attrs) returning {:ok, struct} / {:error, changeset}

Data Patterns

Repository Pattern:

Language	Idiomatic Form
TypeScript	interface UserRepository { findById(id: string): Promise<User | null> }
Go	type UserRepository interface { FindByID(ctx context.Context, id string) (*User, error) }
Rust	trait UserRepository { async fn find_by_id(&self, id: &str) -> Result<Option<User>>; }
C#	interface IUserRepository { Task<User?> FindByIdAsync(string id); }
Java	public interface UserRepository extends JpaRepository<User, String> { }
Elixir	@behaviour with {:ok, t()} | {:error, :not_found} return types

Error Propagation (cross-cutting):

Language	Pattern
TypeScript	throw new AppError('context', { cause: error })
Go	fmt.Errorf("functionName: %w", err) — always wrap with context
Rust	.context("what failed")? (anyhow) or custom error types (thiserror)
C#	throw new AppException("context", ex) — inner exception chaining
Java	throw new AppException("context", e) — cause chaining
Swift	throw AppError.operationFailed(context: "what failed", cause: error)
Kotlin	throw AppException("context", cause = e) — cause chaining
Elixir	{:error, reason} tuples, with chains for multi-step operations

Integration Patterns

Adapter Pattern:

Language	Idiomatic Form
TypeScript	class StripeAdapter implements PaymentGateway { async charge(amount: Money) { ... } }
Go	type stripeAdapter struct { client *stripe.Client } implementing PaymentGateway interface
Rust	struct StripeAdapter { client: StripeClient } impl PaymentGateway for StripeAdapter { ... }
C#	class StripeAdapter : IPaymentGateway { ... } registered via DI
Java	@Component class StripeAdapter implements PaymentGateway { ... }

Enforcement Checklist

When reviewing or implementing:

• Follows existing patterns in codebase
• No new patterns without justification
• Consistent naming with existing code
• Proper layer separation (controller → service → repository)
• Dependencies injected, not instantiated
• Configuration externalized
• Error propagation follows language idiom

Deviation Handling

If you need to deviate from patterns:

1. Document the deviation — Why is this different?
2. Justify the choice — What benefit does it provide?
3. Consider alternatives — Can the pattern be extended instead?
4. Flag for review — Architectural changes need team buy-in

Anti-Patterns to Catch

Anti-Pattern	Fix
God object	Split into focused classes/structs
Spaghetti dependencies	Introduce proper layering
Hardcoded integrations	Use adapter pattern
Scattered business logic	Centralize in services
Direct DB in controllers	Use repository pattern

Output When Enforcing

## Pattern Analysis

**Existing patterns found:**
- [Pattern 1]: Used in [files]
- [Pattern 2]: Used in [files]

**Recommendation:**
Follow [pattern] as used in [example file].

**If deviating:**
Deviation from [pattern] because [reason].