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Part VI: Architectural Principles and Design Patterns

Part VI of the C# Mastery Guide delves into advanced architectural principles and design patterns, focusing on how to structure C# applications for maintainability, scalability, and extensibility. This section covers essential design patterns, SOLID principles, and Dependency Injection, providing a comprehensive understanding of modern C# architecture.

Table of Contents

25. Design Patterns in Modern C#

• 25.1. Creational Patterns with C#:
  • Singleton: Thread-safe lazy initialization and alternatives using modern C#.
  • Factory Method & Abstract Factory: Implementing factories with interfaces, delegates, and integration with dependency injection.
  • Builder: Creating complex objects step-by-step, including fluent APIs and leveraging modern C# features like records with with expressions.
• 25.2. Structural Patterns with C#:
  • Adapter: Adapting existing interfaces to new requirements, using implicit/explicit interface implementations.
  • Decorator: Dynamically extending functionality through composition, often with extension methods or wrapper classes.
  • Proxy: Implementing virtual, remote, or protection proxies using runtime interception or static proxies.
• 25.3. Behavioral Patterns with C#:
  • Strategy: Defining a family of algorithms and making them interchangeable, often implemented with delegates, interfaces, or static abstract members in interfaces (Generic Math).
  • Observer: Implementing a publish-subscribe mechanism using the event keyword, IObservable<T>, and IObserver<T>.
  • Command: Encapsulating requests as objects, enabling undo operations and command queues.
  • Iterator (revisited): A deeper look at custom iterators and the yield keyword’s state machine in the context of the Iterator pattern.
• 25.4. Anti-Patterns and C# Idioms: Common pitfalls and how modern C# features (e.g., LINQ, Nullable Reference Types, records) offer more idiomatic and safer alternatives to traditional pattern implementations.

26. Architectural Principles: SOLID and Beyond

• 26.1. Introduction to Architectural Principles: Understanding why design principles are crucial for building maintainable, scalable, and extensible C# applications; distinguishing between architectural patterns and fundamental principles.
• 26.2. The Single Responsibility Principle (SRP): Defining a single, clear reason for a C# class or module to change, focusing on cohesion, and identifying and refactoring common SRP violations.
• 26.3. The Open/Closed Principle (OCP): Designing C# code that is open for extension but closed for modification, leveraging techniques like inheritance, interfaces, delegates, and generics to achieve behavioral extension without altering existing code.
• 26.4. The Liskov Substitution Principle (LSP): Ensuring that subtypes can be used interchangeably with their base types without introducing unexpected behavior or breaking the application; understanding behavioral subtyping and common LSP pitfalls in C#.
• 26.5. The Interface Segregation Principle (ISP): Creating focused, client-specific interfaces rather than large, general-purpose ones, improving code clarity and reducing unwanted dependencies in C# designs.
• 26.6. The Dependency Inversion Principle (DIP): Depending on abstractions (interfaces or abstract classes) rather than concrete implementations, laying the groundwork for flexible and testable C# architectures, and connecting to Dependency Injection.
• 26.7. Other Guiding Principles: Exploring additional essential principles such as DRY (Don’t Repeat Yourself) for effective code reuse, KISS (Keep It Simple, Stupid) for minimizing complexity, and YAGNI (You Aren’t Gonna Need It) for avoiding over-engineering in C# projects.
• 26.8. Applying Principles in Practice: Practical C# case studies and refactoring examples that demonstrate how to apply SOLID principles and other guidelines to improve real-world code quality and design.

27. Dependency Injection and Inversion of Control

• 27.1. Understanding Inversion of Control (IoC): Grasping the fundamental concept of IoC as a shift in control flow, where a framework or container dictates object creation and lifecycle, contrasting it with traditional, imperative control.
• 27.2. Dependency Injection (DI) as an IoC Pattern: Defining Dependency Injection as a specific implementation of IoC where dependencies are “injected” from the outside; exploring the primary types: Constructor Injection, Property Injection, and Method Injection in C#.
• 27.3. The Role of DI Containers: Understanding the purpose of DI containers in automating dependency resolution and object graph creation, contrasting container-managed DI with manual dependency wiring for C# applications.
• 27.4. Built-in .NET Core DI Container Deep Dive: A comprehensive look at IServiceCollection for service registration and IServiceProvider for service resolution, detailing the three core service lifetimes: Transient, Scoped, and Singleton with practical C# usage.
• 27.5. Advanced DI Scenarios and Patterns: Exploring more complex DI use cases such as conditional registration, dynamic factories for creating services, implementing the Decorator pattern using DI, and handling scenarios where multiple implementations of an interface need to be resolved.
• 27.6. Lifetime Management Nuances and Pitfalls: In-depth discussion of common issues arising from incorrect lifetime management (e.g., singleton services consuming scoped dependencies), strategies for avoiding them, and considerations for asynchronous service resolution.
• 27.7. Testing with Dependency Injection: Demonstrating how DI inherently facilitates writing highly testable C# code, including techniques for mocking and stubbing dependencies in unit and integration testing contexts.
• 27.8. Under the Hood of DI Containers (Briefly): A high-level overview of the internal mechanisms DI containers employ for performance and flexibility, such as reflection, expression trees, or source generators, connecting back to metaprogramming concepts.

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Where to Go Next

• Part I: The .NET Platform and Execution Model: Delving into the foundational environment of .NET and how C# code is compiled and executed.
• Part II: Types, Memory, and Core Language Internals: Exploring the fundamental concepts of C# types, memory management, and the Common Language Runtime’s inner workings.
• Part III: Core C# Types: Design and Deep Understanding: Mastering the essential building blocks of C# code, from object-oriented principles with classes and structs to modern type design and nullability.
• Part IV: Advanced C# Features: Generics, Patterns, LINQ, and More: Unlocking C#’s powerful and expressive features, delving into new programming paradigms, dynamic capabilities, and low-level compiler interactions.
• Part V: Concurrency, Performance, and Application Lifecycle: Covering critical aspects of building and maintaining high-performance C# applications, including asynchronous programming, optimization, debugging, and deployment.
• Appendix: A collection of resources, practical checklists, and a glossary to support the learning journey.