Coding Architecture: SOLID & Clean Design

Great coding architecture ensures that your codebase is maintainable, testable, and adaptable to change over time.

🏗️ 1. SOLID Principles

The five foundational principles of object-oriented design.

S: Single Responsibility Principle (SRP): A class should have only one reason to change.
O: Open/Closed Principle (OCP): Software entities should be open for extension but closed for modification.
L: Liskov Substitution Principle (LSP): Subclasses should be substitutable for their base classes without breaking the application.
I: Interface Segregation Principle (ISP): Clients should not be forced to depend on interfaces they do not use.
D: Dependency Inversion Principle (DIP): Depend on abstractions, not on concretions. High-level modules should not depend on low-level modules.

🚀 2. Clean Architecture (Hexagonal/Onion)

A layered approach where the Domain (Entities) sits at the center, surrounded by Use Cases, Adapters, and finally External Systems (DB, API, UI).

The Rule: Dependencies only point inward.
Benefits: The core business logic is independent of the UI, database, or external frameworks.

📊 3. Domain-Driven Design (DDD)

Focus on the core domain and domain logic. It uses a Ubiquitous Language that both technical and non-technical stakeholders understand.

Aggregate Roots: A cluster of objects treated as a single unit for data changes.
Value Objects: Objects that are defined by their attributes rather than a unique identity (e.g., Money, Address).

🛠️ 4. Gang of Four (GoF) Patterns: The Complete List

The 23 original patterns are divided into three categories based on their purpose.

Creational Patterns (Object Creation)

Name	Purpose
Factory Method	Define an interface for creating an object, but let subclasses decide which class to instantiate.
Abstract Factory	Create families of related objects without specifying their concrete classes.
Builder	Construct complex objects step-by-step.
Singleton	Ensure a class has only one instance and provides a global access point.
Prototype	Copy existing objects without making your code dependent on their classes.

Structural Patterns (Object Assembly)

Name	Purpose
Adapter	Allow incompatible interfaces to work together (The “Bridge” between systems).
Bridge	Split a large class into two separate hierarchies: Abstraction and Implementation.
Composite	Compose objects into tree structures to represent part-whole hierarchies.
Decorator	Attach new behaviors to objects by placing them inside wrapper objects.
Facade	Provide a simplified interface to a complex library or framework.
Flyweight	Share common parts of state between multiple objects to save RAM.
Proxy	Provide a substitute or placeholder for another object to control access.

Behavioral Patterns (Communication)

Name	Purpose
Chain of Responsibility	Pass requests along a chain of handlers.
Command	Turn a request into a stand-alone object containing all information about the request.
Iterator	Traverse elements of a collection without exposing its underlying representation.
Mediator	Restrict direct communications between objects and force them to collaborate via a mediator.
Memento	Save and restore the previous state of an object without revealing its implementation.
Observer	Define a subscription mechanism to notify multiple objects about events.
State	Let an object alter its behavior when its internal state changes.
Strategy	Define a family of algorithms and make them interchangeable.
Template Method	Define the skeleton of an algorithm in the superclass but let subclasses override steps.
Visitor	Separate algorithms from the objects on which they operate.
Interpreter	A way to include language elements in a program.

💡 Best Practices

DRY (Don’t Repeat Yourself): Avoid logic duplication across the codebase.
KISS (Keep It Simple, Stupid): Avoid over-engineering. If a simple solution works, use it.
YAGNI (You Ain’t Gonna Need It): Don’t add features until they are actually needed.
TDD (Test-Driven Development): Write tests first to drive the design and ensure reliability.