Design Patterns Skill

Triggers

• design pattern
• refactor pattern
• strategy pattern
• observer pattern
• factory pattern
• singleton

Purpose

To improve code maintainability, flexibility, and readability by applying proven solutions to common design problems.

Supported Patterns (2025 Context)

Creational

• Factory / Builder: For complex object construction (e.g., configuring LLM clients).
• Singleton: Use sparingly (e.g., for Database connections or Logging service).

Structural

• Adapter: Connecting legacy code or external APIs (e.g., standardizing different LLM APIs).
• Facade: Simplifying complex subsystems (e.g., a simple WebScraper class wrapping Puppeteer).
• Composite: For tree structures (e.g., parsing code ASTs).

Behavioral

• Strategy: Swappable algorithms (e.g., switching between 'Fast' and 'Smart' search).
• Observer: Event handling (e.g., updating UI when data changes).
• State: Managing complex entity lifecycles (e.g., Order status: Pending -> Paid -> Shipped).

Modern / Cloud

• Circuit Breaker: Preventing cascading failures in distributed calls.
• Sidecar: Offloading infra concerns (logging, proxying) to a separate process/container.
• BFF (Backend for Frontend): API layer tailored to specific UIs.

Instructions

1. Identify the Problem: "I have a lot of if/else statements for different payment methods."
2. Match Pattern: "This looks like a use case for the Strategy Pattern."
3. Refactor:
   • Define the Interface.
   • Implement Concrete Strategies.
   • Inject the Strategy into the Context.
4. Document: Add a comment or use DESIGN_PATTERN_USAGE.md if complex.

Anti-Patterns to Avoid

• God Object: Class that does everything.
• Golden Hammer: Using the same pattern everywhere (e.g., everything is a Singleton).