GoF Design Patterns

Goal

• Choose the simplest design that solves the real change pressure.

• Select one primary pattern (two only if responsibilities are clearly split).

• Keep recommendations language-agnostic and explicit about tradeoffs.

• Support coding tasks with pattern-aligned implementation guidance.

Simple Workflow

• Capture context with three questions: what changes often, what hurts now, and which constraint dominates.

• Shortlist up to three candidates using references/DECISION_FRAMEWORK.md (canonical source). Use references/CATALOG.md only for quick intent lookup.

• Select one pattern (or do not use a pattern ) based on future change-cost reduction and lower indirection.

• If the task includes code changes, always read both:

• references/pattern-<selected-pattern>.md

• scripts/<selected-pattern>.ts (illustrative reference only)

• Apply the design incrementally, adapted to the project language and constraints.

• Validate with references/PITFALLS.md , then run a final quality/activation self-check with references/TESTS.md , and format the answer with references/OUTPUT_TEMPLATES.md .

Core Rules

• Language first: choose by problem forces and context, not by language syntax.

• Simplicity first: if recurring change pressure is weak, explicitly recommend do not use a pattern .

• Script policy: scripts are examples to read and adapt, not mandatory to execute.

Output Contract

• Always provide an explicit decision.

• Always include one simpler alternative and why it was rejected.

• Always include tradeoffs (Pros and Cons ).

• If code is shown, include a short adaptation note for other languages.

Navigation

Core References

• Decision Framework

• Catalog

• Pitfalls and Anti-Patterns

• Output Templates

• Trigger Tests

Pattern Cards

• Abstract Factory

• Adapter

• Bridge

• Builder

• Chain of Responsibility

• Command

• Composite

• Decorator

• Facade

• Factory Method

• Flyweight

• Interpreter

• Iterator

• Mediator

• Memento

• Observer

• Prototype

• Proxy

• Singleton

• State

• Strategy

• Template Method

• Visitor