design-patterns

Design Patterns

Purpose

Guide pattern selection across all categories — GoF, enterprise, integration, concurrency, architectural — with decision trees, applicability rules, trade-off analysis, and composition guidance.

Agent Protocol

Trigger

User request includes: design pattern, gof, gang of four, pattern catalog, creational, structural, behavioral, pattern selection, enterprise pattern, integration pattern, concurrency pattern, architectural pattern, anti-pattern, pattern composition, CQRS, event sourcing, saga, repository, unit of work, messaging pattern, circuit breaker, strangler fig, saga pattern, hexagonal architecture, clean architecture.

Input Context

• Problem statement with constraints (performance, memory, team size, tech stack)
• Current architecture description
• Existing patterns already in use
• Pattern category preference or openness

Output Artifact

Selected pattern(s) with rationale, rejected candidates with explicit elimination reasons, implementation sketch, trade-off table, and composition rules if multiple patterns are needed.

Response Format

No preamble. No postamble. No explanations. Strip articles a/an/the where unambiguous. Compress output. If no pattern fits, output No matching pattern. Consider: [alternative approach]. and stop.

Completion Criteria

• Decision tree traversed and documented
• Rejected candidates include explicit elimination reason
• Implementation sketch covers pattern structure (not full business logic)
• Trade-offs documented for each selected pattern
• Pattern composition rules applied if multiple patterns

Architecture Decision Tree

Which Pattern Category?

What kind of problem are you solving?
  ├── Object creation, instance management → Creational (Singleton, Factory, Builder, Prototype)
  ├── Class/object composition, interfaces → Structural (Adapter, Decorator, Proxy, Facade)
  ├── Object communication, algorithms → Behavioral (Observer, Strategy, Command, State)
  ├── Business logic organization, persistence → Enterprise (Repository, Unit of Work, Aggregate)
  ├── Service-to-service communication → Integration (Message Queue, Event Bus, API Gateway)
  ├── Thread safety, async coordination → Concurrency (Mutex, Semaphore, Actor, Fan-out/Fan-in)
  ├── High-level system structure → Architectural (Clean Architecture, Hexagonal, CQRS, Event Sourcing)
  └── Code smells affecting maintainability → Anti-Pattern to refactor (God Class, Spaghetti Code)