C# is a different language than it was a decade ago.

Since async/await landed in C# 5, the language has shipped ninety-two features: records, pattern matching, nullable reference types, Span, source generators, primary constructors, collection expressions, extension members, the field keyword. Each one solves a specific problem. Together, they've changed how modern C# is written, read, and debugged.

Keeping Up with C# is a thematic tour of those ninety-two features. Not a reference — the Microsoft docs are the reference, and they're good. This is the book that walks you through what changed, why it changed, and how the features compose into patterns you can actually reach for in production code.

Instead of marching version by version, chapters group features by the problem they solve: expressiveness, data modeling, pattern matching, type-system flexibility, safety, memory and allocation control, native interop, async, and compiler tooling. The capstone chapter then assembles everything into seven composite patterns — Immutable Data, Null-Safe API, Zero-Allocation, Scripting, Source Generator, Generic Math, and Async Pipeline — the shapes modern C# codebases are actually built from.

Every code snippet is quoted verbatim from one of five MIT-licensed companion projects: QuantLite (a financial trade modeler), DevScripts (a developer toolbox with a working Roslyn source generator), ChatStream (a real-time messaging pipeline), TypeForge (a type-system playground), and PerfBench (a benchmarking harness). Clone any one of them and dotnet run works. Each chapter ends with practice exercises, and Appendix C walks through every solution.

The book is written for three readers: the developer who learned C# 5 or 6 and feels the language moved on without them; the developer arriving from Java, Go, TypeScript, or Rust who needs to know what's idiomatic and what's legacy; and the team lead deciding what to adopt in an existing codebase — Appendix A, the Migration & Adoption Guide, covers LangVersion strategy, nullable reference types rollout, .editorconfig enforcement, and a four-tier adoption priority matrix.

What this book is not: a beginner's guide. It assumes you read C# 5 fluently and nothing past C# 7.

Everything targets C# 14 on .NET 10 LTS (supported until November 2028). All you need is the .NET 10 SDK and any editor.

Keeping Up with C#

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