Design Patterns Explained: GoF & Modern Patterns with Real-World Examples

In software development, Design Patterns act as proven solutions to common problems. Instead of reinventing the wheel, developers can apply these reusable patterns to build scalable, maintainable, and robust applications.

This article explains Gang of Four (GoF) design patterns and also highlights modern design patterns widely used in cloud, microservices, and enterprise systems.

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📌 What Are Design Patterns?

Design patterns are general, reusable solutions to recurring software problems. They are not code snippets but guidelines on how to solve design challenges effectively.

Benefits of using design patterns:

• Improve code reusability & readability

• Promote best practices & standardization

• Reduce development & maintenance time

• Help in team communication (common vocabulary)

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🏛 Gang of Four (GoF) Design Patterns

The GoF introduced 23 design patterns in their famous book "Design Patterns: Elements of Reusable Object-Oriented Software".

They are categorized into three groups:

1. Creational Patterns – Object creation

Help in creating objects without exposing the creation logic.

• Singleton → Ensures only one instance exists.

  public sealed class Logger
  {
      private static readonly Logger _instance = new Logger();
      private Logger() { }
      public static Logger Instance => _instance;
  }
  

  ✅ Used in logging, caching, config management.

• Factory Method → Subclasses decide object creation.

• Abstract Factory → Create families of related objects.

• Builder → Step-by-step object construction.

• Prototype → Clone objects without depending on their class.

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2. Structural Patterns – Class & object composition

Define how objects are composed for flexibility.

• Adapter → Converts one interface into another.
  ✅ Example: Wrapping an old payment gateway API to fit into a new e-commerce app.

• Decorator → Add responsibilities dynamically.

• Facade → Provide a simple interface to a complex system.

• Composite → Treat individual & group objects uniformly (tree structure).

• Proxy → Control access (like lazy loading, security).

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3. Behavioral Patterns – Object communication

Define how objects interact & responsibilities are distributed.

• Observer → One-to-many dependency.

  public interface IObserver { void Update(string msg); }
  public class User : IObserver
  {
      private string _name;
      public User(string name) => _name = name;
      public void Update(string msg) => Console.WriteLine($"{_name} got update: {msg}");
  }
  public class NotificationService
  {
      private List<IObserver> observers = new();
      public void Subscribe(IObserver o) => observers.Add(o);
      public void Notify(string msg)
      {
          foreach (var o in observers) o.Update(msg);
      }
  }
  

  ✅ Used in push notifications, event-driven systems.

• Strategy → Choose algorithm at runtime.

• Command → Encapsulate actions as objects.

• State → Change behavior based on object state.

• Mediator, Memento, Interpreter, Visitor, Template Method, Chain of Responsibility, Iterator.

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🚀 Modern / New Design Patterns (Beyond GoF)

Today’s software systems (Cloud, Microservices, Big Data, AI) need patterns beyond GoF. Here are some important ones:

1. Dependency Injection (DI)

• Promotes loose coupling by injecting dependencies instead of creating them inside a class.

• Widely used in .NET Core, Spring Boot, Angular.

  public class OrderService
  {
      private readonly IPaymentGateway _paymentGateway;
      public OrderService(IPaymentGateway paymentGateway) => _paymentGateway = paymentGateway;
      public void PlaceOrder() => _paymentGateway.Process();
  }
  

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2. Repository Pattern

• Abstracts database access to keep business logic independent.

• Used in DDD (Domain-Driven Design) and enterprise apps.

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3. CQRS (Command Query Responsibility Segregation)

• Separates read and write operations for better scalability.

• Common in microservices + event sourcing.

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4. Saga Pattern (Microservices)

• Handles distributed transactions across microservices.

• Uses event-driven orchestration or choreography to maintain consistency.

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5. Event Sourcing

• State changes are stored as events (not just final values).

• Used in banking, e-commerce order history, blockchain-like systems.

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6. Circuit Breaker Pattern

• Prevents cascading failures by stopping requests to a failing service.

• Implemented in Polly (.NET), Resilience4j (Java).

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7. API Gateway Pattern

• Acts as a single entry point for microservices.

• Handles routing, load balancing, authentication, caching.

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8. Strangler Fig Pattern

• Gradually replaces legacy systems by routing new features to modern services while old ones still run.

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🔑 Conclusion

• GoF Patterns are still foundational for object-oriented design.

• Modern patterns are essential for cloud, distributed systems, and microservices.

• By combining both, developers can build scalable, reliable, and future-proof applications.