Design Patterns Mastery
1. Introduction to Design Patterns
Introduction to GoF Patterns: Why patterns matter? SOLID Principles: The foundation of all patterns DRY, KISS, and YAGNI (Architectural Philosophy)
2. Creational Patterns
Singleton Pattern: Thread-safety & Captive Dependencies Factory Method: Abstracting complex object creation Abstract Factory: Creating families of related objects Builder Pattern: Constructing complex fluents Prototype Pattern: Cloning high-cost objects
3. Structural Patterns
Adapter Pattern: Bridging incompatible interfaces Bridge Pattern: Decoupling abstraction from implementation Composite Pattern: Managing tree structures & hierarchies Decorator Pattern: Enhancing behavior without inheritance Facade Pattern: Simplifying complex library subsystems Flyweight Pattern: Drastically reducing memory footprint Proxy Pattern: Interception, Lazy-Loading, and Security
4. Behavioral Patterns
Chain of Responsibility: Middleware & Pipeline Architecture Command Pattern: Implementing Undo/Redo & Queueing Interpreter Pattern: Building domain-specific languages Iterator Pattern: Unified traversal of collections Mediator Pattern: Decoupling components with MediatR Memento Pattern: Capturing and restoring object state Observer Pattern: Pub/Sub & Event-driven architecture State Pattern: Managing complex object lifecycles Strategy Pattern: Swappable algorithms at runtime Template Method: Defining skeleton algorithms Visitor Pattern: Separating operations from data structures
5. Modern Enterprise & Cloud Patterns
Repository & Unit of Work (The EF Core Standard) CQRS Pattern (Command Query Responsibility Segregation) Circuit Breaker & Retry Patterns (Resilience with Polly) Dependency Injection Pattern (The Modern King)
Design Patterns Mastery

Introduction to GoF Patterns: Why patterns matter?

2 Views Updated 5/6/2026

Introduction to GoF Patterns

In 1994, four authors (known as the Gang of Four) published a book that changed software engineering forever. They identified 23 recurring problems in object-oriented software and provided "Blueprints" for solving them. These aren't code libraries; they are Patterns of Thought.

1. What is a Design Pattern?

A design pattern is NOT a specific piece of code. It is a general, reusable solution to a commonly occurring problem within a given context in software design. Think of it as a "Shared Vocabulary" between developers. When an architect says, "Let's use a Decorator here," everyone knows exactly what the architecture will look like without writing a single line of code.

2. The Three Categories of Patterns

The GoF patterns are divided into three buckets based on what they do:

  • Creational: Deal with object creation mechanisms, trying to create objects in a manner suitable to the situation.
  • Structural: Deal with object composition, making sure that if one part of a system changes, the entire system doesn't need to change.
  • Behavioral: Deal with communication between objects, ensuring that data and responsibility flow smoothly.

3. Why patterns are dangerous in the wrong hands

The most common mistake junior developers make is "Pattern Over-Engineering." They try to force a pattern into every single class. This leads to code that is impossible to read. Patterns should be used to DECREASE complexity, not increase it. If a simple 'if' statement works, you don't need a Strategy Pattern.

4. Interview Mastery

Q: "Can you name a design pattern currently used within the .NET Core Framework itself?"

Architect Answer: "Absolutely. The `Middleware` pipeline in ASP.NET Core is a perfect implementation of the **Chain of Responsibility** pattern. Every time you use `app.UseRouting()`, you are adding a link to a chain. Each link decides whether to process the HTTP request or pass it to the next link. Another example is `HttpClientFactory`, which is a **Factory Pattern** used to manage the lifecycle of sockets and prevent DNS-related memory leaks."

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Design Patterns Mastery
1. Introduction to Design Patterns
Introduction to GoF Patterns: Why patterns matter? SOLID Principles: The foundation of all patterns DRY, KISS, and YAGNI (Architectural Philosophy)
2. Creational Patterns
Singleton Pattern: Thread-safety & Captive Dependencies Factory Method: Abstracting complex object creation Abstract Factory: Creating families of related objects Builder Pattern: Constructing complex fluents Prototype Pattern: Cloning high-cost objects
3. Structural Patterns
Adapter Pattern: Bridging incompatible interfaces Bridge Pattern: Decoupling abstraction from implementation Composite Pattern: Managing tree structures & hierarchies Decorator Pattern: Enhancing behavior without inheritance Facade Pattern: Simplifying complex library subsystems Flyweight Pattern: Drastically reducing memory footprint Proxy Pattern: Interception, Lazy-Loading, and Security
4. Behavioral Patterns
Chain of Responsibility: Middleware & Pipeline Architecture Command Pattern: Implementing Undo/Redo & Queueing Interpreter Pattern: Building domain-specific languages Iterator Pattern: Unified traversal of collections Mediator Pattern: Decoupling components with MediatR Memento Pattern: Capturing and restoring object state Observer Pattern: Pub/Sub & Event-driven architecture State Pattern: Managing complex object lifecycles Strategy Pattern: Swappable algorithms at runtime Template Method: Defining skeleton algorithms Visitor Pattern: Separating operations from data structures
5. Modern Enterprise & Cloud Patterns
Repository & Unit of Work (The EF Core Standard) CQRS Pattern (Command Query Responsibility Segregation) Circuit Breaker & Retry Patterns (Resilience with Polly) Dependency Injection Pattern (The Modern King)