Preface – C# 8.0 in a Nutshell


C# 8.0 represents the seventh major update to Microsoft’s flagship programming language, positioning C# as a language with unusual flexibility and breadth. At one end, it offers high-level abstractions such as query expressions and asynchronous continuations, whereas at the other end, it allows low-level efficiency through constructs such as custom value types and optional pointers.

The price of this growth is that there’s more than ever to learn. Although tools such as Microsoft’s IntelliSense—and online references—are excellent in helping you on the job, they presume an existing map of conceptual knowledge. This book provides exactly that map of knowledge in a concise and unified style—free of clutter and long introductions.

Like the past five editions, C# 8.0 in a Nutshell is organized around concepts and use cases, making it friendly both to sequential reading and to random browsing. It also plumbs significant depths while assuming only basic background knowledge, making it accessible to intermediate as well as advanced readers.

This book covers C#, the Common Language Runtime (CLR), and the essential .NET Core assemblies. We’ve chosen this focus to allow space for difficult topics such as concurrency, security, and access to operating system functionality—without compromising depth or readability. Features new to C# 8 are flagged so that you can also use this book as a reference for C# 7.

Intended Audience

This book targets intermediate to advanced audiences. No prior knowledge of C# is required, but some general programming experience is necessary. For the beginner, this book complements, rather than replaces, a tutorial-style introduction to programming.

This book is an ideal companion to any of the vast array of books that focus on an applied technology such as ASP.NET Core, Windows Presentation Foundation (WPF), and Universal Windows Platform (UWP). The areas of the language and .NET Core that such books omit, C# 8.0 in a Nutshell covers in detail, and vice versa.

If you’re looking for a book that skims every .NET technology, this is not for you. This book is also unsuitable if you want to learn about APIs specific to mobile device development.

How This Book Is Organized

Chapters 2 through 4 concentrate purely on C#, starting with the basics of syntax, types, and variables, and finishing with advanced topics such as unsafe code and preprocessor directives. If you’re new to the language, you should read these chapters sequentially.

The remaining chapters cover essential elements of .NET Core, including such topics as Language-Integrated Query (LINQ), XML, collections, concurrency, I/O and networking, memory management, reflection, dynamic programming, attributes, security, and native interoperability. You can read most of these chapters randomly, except for Chapters 5 and 6, which lay a foundation for subsequent topics. You’re also best off reading the three chapters on LINQ in sequence, and some chapters assume some knowledge of concurrency, which we cover in Chapter 14.

What You Need to Use This Book

The examples in this book require .NET Core 3. You will also find Microsoft’s .NET documentation useful to look up individual types and members (which is available online).

Although it’s possible to write source code in Notepad and build your program from the command line, you’ll be much more productive with a code scratchpad for instantly testing code snippets, plus an Integrated Development Environment (IDE) for producing executables and libraries.

For a Windows code scratchpad, download LINQPad 6 from (free). LINQPad fully supports C# 8.0 and is maintained by one of the authors.

For a Windows IDE, download Visual Studio 2019: any edition is suitable for what’s taught in this book. For a cross-platform IDE, download Visual Studio Code.


All code listings for all chapters are available as interactive (editable) LINQPad samples. You can download the entire lot in a single click: at the bottom left, click the LINQPad’s Samples tab, click “Download more samples,” and then choose “C# 8.0 in a Nutshell.”

.NET Core is available for Windows, Linux, and macOS. Certain cross-platform features were tested on Ubuntu Linux 18.04. That code is available on GitHub.

Conventions Used in This Book

The book uses basic UML notation to illustrate relationships between types, as shown in Figure P-1. A slanted rectangle means an abstract class; a circle means an interface. A line with a hollow triangle denotes inheritance, with the triangle pointing to the base type. A line with an arrow denotes a one-way association; a line without an arrow denotes a two-way association.

Figure P-1. Sample diagram

The following typographical conventions are used in this book:

Indicates new terms, URIs, filenames, and directories
Constant width
Indicates C# code, keywords and identifiers, and program output
Constant width bold
Shows a highlighted section of code
Constant width italic
Shows text that should be replaced with user-supplied values

This element signifies a general note.

Using Code Examples

This book is here to help you get your job done. In general, you may use the code in this book in your programs and documentation. You do not need to contact us for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission (although we appreciate attribution). Incorporating a significant amount of example code from this book into your product’s documentation does require permission.

If you feel your use of code examples falls outside fair use or the permission given here, feel free to contact us at

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Joseph Albahari

First, I want to thank Eric Johannsen for his help on this edition—particularly for his work in making the book Unix friendly. I also want to thank my brother, Ben Albahari, for his contributions on earlier editions.

It’s been an honor to have superb technical reviewers on the team. I’d like to extend particular thanks to Vitek Karas and Stephen Toub from Microsoft for providing invaluable feedback at a busy time. Also, my thanks to Paulo Morgado, Aaron Robinson, Jan Vorlicek, and Sam Gentile for their contributions.

The book was built on previous editions, whose technical reviewers I owe a similar honor: in the past two editions, Rod Stephens, Jared Parsons, Stephen Toub, Matthew Groves, Dixin Yan, Lee Coward, Bonnie DeWitt, Wonseok Chae, Lori Lalonde, and James Montemagno. And in previous editions, Eric Lippert, Jon Skeet, Stephen Toub, Nicholas Paldino, Chris Burrows, Shawn Farkas, Brian Grunkemeyer, Maoni Stephens, David DeWinter, Mike Barnett, Melitta Andersen, Mitch Wheat, Brian Peek, Krzysztof Cwalina, Matt Warren, Joel Pobar, Glyn Griffiths, Ion Vasilian, Brad Abrams, and Adam Nathan.

I appreciate that many of the technical reviewers are accomplished individuals at Microsoft, and I particularly thank you for taking the time to raise this book to the next quality bar.

I want to thank the O’Reilly team—particularly my efficient and responsive editor Corbin Collins. Finally, my deepest thanks to my wonderful wife, Li Albahari, whose presence kept me happy throughout the project.

Eric Johannsen

It’s remarkable how the internet allows collaboration with some of the world’s smartest people from the confines of my home office.

I thank Joseph Albahari for inviting me to collaborate on this amazing project.

The Microsoft employees and community members who collaborate on .NET Core on GitHub are tremendously responsive and helpful. If I couldn’t find a solution to a tricky question already documented there, my own questions were answered in short order. Thank you for your support.

I wouldn’t have been able to accept Joseph’s offer without the loving support of my family. I thank my wife, Rose, for picking up the slack during this busy time, and my triplet children, Sydney, Alexis, and Ryan, for their understanding.