Why mastering C# still matters in the age of AI AI is a powerful tool, but for critical systems, it cannot replace human judgment and oversight. Only when developers maintain genuine ownership of their code can they effectively manage technical debt and maintenance costs over the long term. So yes, mastering programming languages and APIs matters more than ever. However, this is not an exhaustive C# reference. Instead, this book focuses on the essential, advanced, and practical aspects of C# that require deep mastery. Unlike traditional programming guides, we emphasize "deep understanding" and encourage you to leverage AI tools to accelerate your development. In an era of AI-generated code, developers need sharper judgment regarding quality, security, and performance—and the skill to precisely direct AI to produce high-quality C# code. Who this book is for This book is for developers who already have a foundation in C# or another programming language and want to dive into modern C# syntax and practical details (C# 14 and .NET 10). We skip the absolute basics to focus on the advanced details that AI often overlooks or misinterprets. This book does NOT cover programming fundamentals, such as: - How to call functions and pass parameters - Basic loops and control flow - Core object-oriented concepts (classes, inheritance, polymorphism) (Even so, Chapter 1 begins with a concise “Hello World” example, allowing developers from other languages to quickly transition into the .NET ecosystem.) Learning approach To help you learn more effectively, this book uses the following approaches to guide your learning: - Side-by-side comparisons: For easily confused concepts, we show both “not recommended” and “recommended” versions and explain why. - Visual aids: Diagrams are used where helpful to clarify complex ideas. - Practice-oriented: Not just “how,” but also “why,” “when to use,” “when not to use,” and the potential performance impact. - Ask AI: You’ll see prompts sprinkled throughout to encourage using AI as a learning aid. - C# version notes: We mark which C# version introduced a feature to help you understand the language’s evolution. - Sample code links: All sample code is published on GitHub, and the book includes links where appropriate. Chapters Preface Chapter 1: Modern environment and fundamentals Chapter 2: Declarations and syntactic sugar Chapter 3: Null safety Chapter 4: Immutable design Chapter 5: Error handling and resource management Chapter 6: Pattern matching Chapter 7: Generics Chapter 8: Delegates and events Chapter 9: LINQ and functional programming Chapter 10: Extension methods Chapter 11: Asynchronous programming Chapter 12: High-performance memory operations Afterword