Design Patterns study guide

My notes on all 23 patterns from Design Patterns (Gamma, Helm, Johnson, Vlissides, 1994). Each pattern uses the same checklist so I can compare them: intent, problem, solution, structure diagram, TypeScript code, when it fits, trade-offs, and where I have already used it.

What’s inside

• Foundations: what a pattern is, encapsulate-what-varies, composition vs inheritance, SOLID, a four-week study plan, diagram notation.
• The 23 patterns: 5 creational, 7 structural, 11 behavioral. Each with a UML class diagram; most also with a runtime view of the code example.
• Applying them: symptom to pattern table, look-alike pairs (Strategy vs State, Proxy vs Decorator vs Adapter vs Facade), a relationship map, over-engineering signals, modern language replacements, and a 60-question self-test.

Pattern names and catalogue structure follow the GoF book. The rest is my wording, diagrams, and code.