Design Patterns

Practical patterns every engineer should know — from classic GoF to modern distributed system patterns.

What You'll Master

Learn 27 design patterns through real-world analogies, BEFORE/AFTER Go code, Mermaid diagrams, and practical guidance on when to use (and when NOT to use) each pattern.

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The Learning Path

#	Chapter	Patterns	Difficulty	~Time
01	Foundations & Creational Patterns	Factory, Builder, Singleton, Prototype	Beginner	40 min
02	Structural Patterns	Adapter, Decorator, Facade, Proxy, Composite, Bridge	Intermediate	45 min
03	Behavioral Patterns	Observer, Strategy, Command, Chain of Responsibility, State, Template Method	Intermediate	45 min
04	Modern Application Patterns	Repository, DI, Middleware, Circuit Breaker, Retry	Intermediate	40 min
05	Distributed System Patterns	CQRS, Event Sourcing, Saga, Strangler Fig, Sidecar	Advanced	45 min
06	Anti-Patterns & Selection Guide	God Object, Golden Hammer, Cargo Cult + Decision Matrix	Intermediate	30 min

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How Each Pattern Is Taught

Every pattern follows a consistent, practical structure:

1. Real-world analogy — "think of it like..."
2. The problem — a concrete scenario, not abstract theory
3. Solution diagram — Mermaid class + sequence diagrams
4. Go code — BEFORE (messy) → AFTER (with pattern applied)
5. When to use / When NOT to use — the most valuable part
6. Real-world usage — frameworks and libraries that use this pattern
7. Related patterns — cross-references within the handbook

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Why This Section Exists

Design patterns are distilled engineering wisdom — recurring solutions to common problems. But most resources teach them as abstract theory. This section takes a different approach:

• Practical first: every pattern starts with a real problem you've faced
• Go-idiomatic: patterns adapted for Go (channels, interfaces, functional options)
• Honest trade-offs: we tell you when a pattern is overkill or harmful
• BEFORE/AFTER code: see the messy code first, then the clean solution

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Total: 27 patterns across 6 chapters · ~4 hours

Inspired by Refactoring.Guru, Head First Design Patterns, and the Go community's practical approach to software design.