# oop-design-patterns

A GitHub Copilot rule that steers code generation and refactoring toward GoF design patterns and SOLID principles in object-oriented code.

- rule · `type=rule` · GitHub Copilot · ★ 40418
- Author: github · official GitHub repository
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/github/awesome-copilot/tree/HEAD/instructions/oop-design-patterns.instructions.md
- Updated: 2026-10-23
- HTML: https://affpapa.org/en/nevibecode/rules/oop-design-patterns

## What it does

The file tells Copilot how to pick a design pattern. It opens with four architectural rules: program to an interface rather than an implementation, favour composition over inheritance, isolate the parts that vary, and keep classes loosely coupled. Then come the three GoF groups with a note on when each fits — creational (Abstract Factory, Factory Method, Builder, Singleton, Prototype), structural (Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy) and behavioral (Strategy, Observer, Command, State, Template Method, Chain of Responsibility, Mediator, Iterator, Visitor, Memento).

A separate section covers code generation. Copilot should write the interface or abstract base class before any concrete implementation, keep fields `private` by default, and name classes so the pattern shows through — `TaxCalculationStrategy`, `WidgetFactory`. Singleton is allowed only where a single instance is genuinely required, and dependency injection is the preferred route. Oversized classes get split and wired together through a Mediator or Strategy objects.

The rule hooks in through `applyTo` and fires on `**/*.py`, `**/*.java`, `**/*.ts`, `**/*.js` and `**/*.cs`. On any other language it stays silent, so check the mask before you expect different suggestions. The instruction text cuts off partway through the Liskov principle, so the SOLID walkthrough may not be complete in the file.

## Install

### GitHub Copilot (native platform)

**Manually: put the files in place**
- File: `.github/instructions/oop-design-patterns.instructions.md` — The applyTo field sets which files it applies to

### Claude Code

**Manually: put the files in place**
- File: `.claude/rules/oop-design-patterns.md` — The paths frontmatter field limits the files: move applyTo from the source into paths

### Codex

**AGENTS.md**
- Codex reads AGENTS.md: paste the rule text there

### Cursor

**Manually: put the files in place**
- File: `.cursor/rules/oop-design-patterns.mdc` — Frontmatter: description, globs, alwaysApply. Move applyTo from the source into globs, or the rule will not attach on its own

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/rules/oop-design-patterns.md`

### Cline

**Manually: put the files in place**
- File: `.clinerules/oop-design-patterns.md`

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/github/awesome-copilot/tree/HEAD/instructions/oop-design-patterns.instructions.md

## When to use it
- pick a pattern for object creation
- replace long `if-else` chains with Strategy
- split a class that grew too large
- make fields private and favour immutability
- decouple a request sender from its receiver

## Example prompts
- Pick a pattern for calculating taxes several ways and note the choice in a comment
- Refactor this class: interface first, implementations after
- I need to undo the last action — which GoF pattern fits?

## Source text · oop-design-patterns.instructions.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 200744553c017f11.

BEGIN THIRD-PARTY FILE 200744553c017f11
```text
---
description: 'Best practices for applying Object-Oriented Programming (OOP) design patterns, including Gang of Four (GoF) patterns and SOLID principles, to ensure clean, maintainable, and scalable code.'
applyTo: '**/*.py, **/*.java, **/*.ts, **/*.js, **/*.cs'
---


# Design Patterns for Object-Oriented Programming for Clean Code

These instructions configure GitHub Copilot to prioritize Gang of Four (GoF) Design Patterns, SOLID principles, and clean Object-Oriented Programming (OOP) practices when generating or refactoring code.

## Core Architectural Philosophy

- **Program to an Interface, not an Implementation:** Always favor abstract classes or interfaces over concrete implementations. Use dependency injection to provide concrete instances.
- **Favor Object Composition over Class Inheritance:** Use composition to combine behaviors dynamically at runtime. Avoid deep inheritance trees. Use Delegation where appropriate to reuse behavior without breaking encapsulation.
- **Encapsulate What Varies:** Identify the aspects of the application that vary and separate them from what stays the same. Use patterns like Strategy, State, or Bridge to isolate these variations.
- **Loose Coupling:** Minimize direct dependencies between classes. Use Mediator, Observer, or abstract factories to keep components decoupled.

## Creational Patterns Guidelines

When generating code that involves object creation or instantiation, apply these patterns to decouple the system from how its objects are created:

- **Abstract Factory:** Use when a system must be configured with one of multiple families of related products (e.g., cross-platform UI widgets). Ensure clients only interact with the abstract factory and abstract product interfaces.
- **Factory Method:** Use when a class cannot anticipate the class of objects it must create. Defer instantiation to subclasses.
- **Builder:** Use when constructing a complex object requires a step-by-step process, especially when the same construction process can yield different representations.
- **Singleton:** Use *only* when absolutely necessary to guarantee a single instance of a class and provide a global access point (e.g., a central configuration manager or a hardware interface). Prefer Dependency Injection over strict Singletons where possible.
- **Prototype:** Use to avoid building a class hierarchy of factories or when creating an object from scratch is more expensive than cloning an existing one.

## Structural Patterns Guidelines

When generating code that defines how classes and objects are composed to form larger structures, apply these patterns:

- **Adapter:** Use to make incompatible interfaces work together. Prefer Object Adapters (using composition) over Class Adapters (using multiple inheritance) for greater flexibility.
- **Bridge:** Use to separate an abstraction from its implementation so the two can vary independently (e.g., separating a high-level `Window` concept from platform-specific `WindowImpl` logic).
- **Composite:** Use to represent part-whole hierarchies. Ensure clients can treat individual objects and compositions of objects uniformly via a common `Component` interface.
```
END THIRD-PARTY FILE 200744553c017f11

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