Albahari J. C# 9.0 in a Nutshell. The Definitive Reference 2021

Textbook in PDF format

When you have questions about C# 9.0 or .NET 5, this best-selling guide has the answers you need. C# is a language of unusual flexibility and breadth, but with its continual growth there's so much more to learn. In the tradition of O'Reilly's Nutshell guides, this thoroughly updated edition is simply the best one-volume reference to the C# language available today.
Organized around concepts and use cases, C# 9.0 in a Nutshell provides intermediate and advanced programmers with a concise map of C# and .NET that also plumbs significant depths.
Get up to speed on C#, from syntax and variables to advanced topics such as pointers, records, closures, and patterns
Dig deep into LINQ with three chapters dedicated to the topic
Explore concurrency and asynchrony, advanced threading, and parallel programming
Work with .NET features, including regular expressions, networking, spans, reflection, and cryptography