patternslisted

# Implementation Patterns Reference for common implementation patterns. Use these patterns to write consistent, maintainable code. ## Iron Law > **FOLLOW EXISTING PATTERNS** > > Match the codebase style, don't invent new conventions. If the project uses Result types, > use Result types. If it uses exceptions, use exceptions. Consistency trumps personal > preference. The best pattern is the one already in use. ## When This Skill Activates - Implementing CRUD operations - Creating API endpoints - Writing event handlers - Setting up configuration - Adding logging - Database operations --- ## Pattern Categories ### CRUD Operations Create, Read, Update, Delete with Result types and proper error handling. **Core pattern**: Validate -> Transform -> Persist -> Return ```typescript async function createUser(input: CreateUserInput): Promise<Result<User, CreateError>> { const validated = validateCreateUser(input); if (!validated.ok) return Err({ type: 'validation', details: validated.error }); const user: User = { id: generateId(), ...validated.value, createdAt: new Date() }; const saved = await userRepository.save(user); if (!saved.ok) return Err({ type: 'persistence', details: saved.error }); return Ok(saved.value); } ``` ### API Endpoints REST endpoint structure with auth, validation, and error mapping. **Core pattern**: Parse request -> Validate auth -> Execute -> Format response ```typescript export async function handleGetUser(req: Request): Promise<Re