C# in Depth (4th Edition)

Introduction

The book "C# in Depth" (4th edition, 2019) by Jon Skeet is not another tutorial for beginners, but an in-depth study of the evolution of the C# language from version 2.0 to 8.0. Skeet, known as one of the most authoritative experts on C# (and the most active participant on Stack Overflow), offers the reader not just a list of new features, but an understanding of why the language evolved the way it did and how these changes affect everyday development.

The book was published in 2019, spans 528 pages, and is aimed at experienced developers who already write in C# and want to move to the next level — from "just working code" to elegant, performant, and safe solutions.

What This Book Is About

"C# in Depth" is structured as a chronology of the language's development. Each chapter is dedicated to a specific version of C# (starting from 2.0) and its key innovations. Main topics:

• Generics — how they changed typing and performance.
• LINQ and Query Expressions — a declarative approach to working with data.
• Asynchronous Programming (async/await) — an in-depth analysis of the task model, synchronization context, and best practices.
• Nullable Reference Types — a new safety system against null references.
• Pattern Matching — from simple checks to complex recursive patterns.
• Records and Read-only Structs — data immutability.
• Span and Memory — low-level memory work without buffer allocation.
• Default Interface Methods — the evolution of abstractions.

Each topic is accompanied not only by syntactic examples but also by an analysis of the internal workings of the compiler and the .NET runtime.

Who This Book Is For

The book is not intended for beginners. If you are just getting acquainted with C# or .NET, it's better to start with "C# 8.0 and .NET Core 3.0" by Mark Price or "Head First C#". "C# in Depth" is a book for:

• Developers with 1–2 years of experience who want to understand "under the hood".
• Those migrating from older versions of C# (e.g., from 5.0 to 8.0) and wanting to master all the new features.
• Architects and team leads making decisions about choosing approaches (e.g., async vs. threads, records vs. classes).
• Programmers preparing for interviews for Senior/Lead positions.

What the Reader Will Learn

After reading, you will be able to:

• Explain the difference between covariance and contravariance in generics.
• Properly design asynchronous APIs without deadlocks.
• Use pattern matching to replace long if-else and switch statements.
• Write safe code with nullable reference types, avoiding NullReferenceException.
• Optimize performance using Span and ref struct.
• Understand how the compiler transforms your constructs into IL code.
• Choose between classes, structs, and records depending on the scenario.

Strengths

• Depth: Skeet doesn't just list features — he explains the motivation behind their introduction, alternatives, and trade-offs.
• Relevance: The 4th edition covers C# 8.0, including nullable reference types, async streams, and indices/ranges.
• Author's Authority: Jon Skeet is a member of the C# development team and author of numerous articles; his explanations are accurate and verified.
• Practical Examples: The code from the book can be immediately applied in real projects.
• Structure: The chronological approach allows you to see the evolution of the language as a single story.

Who It Is Recommended For

I recommend the book to everyone who already writes in C# and wants to stop "just using features" and start understanding them. If you feel that in