> For AI agents: the complete documentation index is available at https://nhanbe.id.vn/llms.txt, the full documentation bundle is available at https://nhanbe.id.vn/llms-full.txt.

# Design Patterns Overview

This section collects GoF patterns with practical examples and guidance. Use it to pick a suitable pattern, not to force one.

## Quick decision guide

- **Object creation is complex** → look at **Creational** patterns.
- **You need to compose behavior** → look at **Structural** patterns.
- **You want flexible interactions** → look at **Behavioral** patterns.

## Common comparisons (quick picks)

- **Strategy vs State**: Strategy is chosen by the client; State changes from within the object.
- **Adapter vs Facade**: Adapter changes an interface; Facade simplifies a subsystem.
- **Decorator vs Proxy**: Decorator adds behavior; Proxy controls access.

## Pattern map (by intent)

| Intent                   | Patterns                |
| ------------------------ | ----------------------- |
| Create one object        | Singleton               |
| Create families          | Abstract Factory        |
| Create step-by-step      | Builder                 |
| Reuse similar objects    | Prototype               |
| Decouple creation        | Factory Method          |
| Adapt interfaces         | Adapter                 |
| Simplify subsystems      | Facade                  |
| Compose trees            | Composite               |
| Add behavior             | Decorator               |
| Control access           | Proxy                   |
| Share state              | Flyweight               |
| Vary implementation      | Bridge                  |
| Chain handlers           | Chain of Responsibility |
| Encapsulate actions      | Command                 |
| Define languages         | Interpreter             |
| Traverse collections     | Iterator                |
| Centralize communication | Mediator                |
| Snapshot state           | Memento                 |
| Notify observers         | Observer                |
| Switch behavior by state | State                   |
| Swap algorithms          | Strategy                |
| Fixed algorithm steps    | Template Method         |
| Add operations           | Visitor                 |

## Next steps

- Start with the closest intent.
- Check “Related patterns” for alternatives.
- If two patterns fit, pick the simpler one.