INTRODUCTION

EVEN THOUGH .NET was announced in the year 2000, it is not becoming a grandfather technology. Instead, .NET keeps increasing developer traction since it has become open source and is available not only on Windows but also on Linux platforms. .NET can also run within the browser on the client-without the need to install a plugin-by using the WebAssembly standard.

As new enhancements for C# and .NET are coming, a focus lies not only on performance gains but also on ease of use. .NET more and more is a choice for new developers.

C# is also attractive for long-term developers. Every year, Stack Overflow asks developers about the most loved, dreaded, and wanted programming languages and frameworks. For several years, C# has been within the top 10 of the most loved programming languages. ASP.NET Core now holds the top position as the most loved web framework. .NET Core is number one in the most loved other frameworks/libraries/tools category. See https://insights.stackoverflow.com/survey/2020 for details.

When you use C# and ASP.NET Core, you can create web applications and services (including microservices) that run on Windows, Linux, and Mac. You can use the Windows Runtime to create native Windows apps using C#, XAML, and .NET. You can create libraries that you share between ASP.NET Core, Windows apps, and .NET MAUI. You can also create traditional Windows Forms and WPF applications.

Most of the samples of this book are built to run on a Windows or Linux system. Exceptions are the Windows app samples that run only on the Windows platform. You can use Visual Studio, Visual Studio Code, or Visual Studio for the Mac as the developer environment; only the Windows app samples require Visual Studio.

THE WORLD OF .NET

.NET has a long history; the first version was released in the year 2002. The new .NET generation with a complete rewrite of .NET (.NET Core 1.0 in the year 2016) is very young. Recently, many features from the old .NET version have been brought to .NET Core to ease the migration experience.

When creating new applications, there is no reason not to move to the new .NET versions. Whether old applications should stay with the old version of .NET or be migrated to the new one depends on the features used, how difficult the migration is, and what advantages you gain after the application is migrated. The best options here need to be considered with an application-by-application analysis.

The new .NET provides easy ways to create Windows and web applications and services. You can create microservices running in Docker containers in a Kubernetes cluster; create web applications; use the new OpenTelemetry standard to analyze distributed traces in a vendor-independent manner; create web applications returning HTML, JavaScript, and CSS; and create web applications returning HTML, JavaScript, and .NET binaries that run in the client's browser in a safe and standard way using WebAssembly. You can create Windows applications in traditional ways using WPF and Windows Forms and make use of modern XAML features and controls that support the fluent design with WinUI and mobile applications with .NET MAUI.

.NET uses modern patterns. Dependency injection is built into core services, such as ASP.NET Core and EF Core, which not only makes unit testing easier but also allows developers to easily enhance and change features from these technologies.

.NET runs on multiple platforms. Besides Windows and macOS, many Linux environments are supported, such as Alpine, CentOS, Debian, Fedora, openSUSE, Red Hat, SLES, and Ubuntu.

.NET is open source (https://github.com/dotnet) and freely available. You can find meeting notes for the C# compiler (https://github.com/dotnet/csharplang), the source code for the C# compiler (https://github.com/dotnet/Roslyn), the .NET runtime and libraries (https://github.com/dotnet/runtime), and ASP.NET Core (https://github.com/dotnet/aspnetcore) with Razor Pages, Blazor, and SignalR.

Here's a summary of some of the features of the new .NET:

• .NET is open source.
• .NET uses modern patterns.
• .NET supports development on multiple platforms.
• ASP.NET Core can run on Windows and Linux.

THE WORLD OF C#

When C# was released in the year 2002, it was a language developed for the .NET Framework. C# was designed with ideas from C++, Java, and Pascal. Anders Hejlsberg had come to Microsoft from Borland and brought experience from the language development of Delphi. At Microsoft, Hejlsberg worked on Microsoft's version of Java, named J++, before creating C#.

NOTE Today, Anders Hejlsberg has moved to TypeScript (although he still influences C#), and Mads Torgersen is the project lead for C#. C# improvements are discussed openly at https://github.com/dotnet/csharplang, and you can read C# language proposals and event meeting notes. You can also submit your own proposals for C#.

C# started not only as an object-oriented general-purpose programming language but was a component-based programming language that supported properties, events, attributes (annotations), and building assemblies (binaries including metadata).

Over time, C# was enhanced with generics, Language Integrated Query (LINQ), lambda expressions, dynamic features, and easier asynchronous programming. C# is not an easy programming language because of the many features it offers, but it's continuously evolving with features that are practical to use. With this, C# is more than an object-oriented or component-based language; it also includes ideas of functional programming-things that are of practical use for a general-purpose language developing all kinds of applications.

Nowadays, a new version of C# is released every year. C# 8 added nullable reference types, and C# 9 added records and more. C# 10 is releasing with .NET 6 in 2021 and C# 11 will be released with .NET 7 in 2022. Because of the frequency of changes nowadays, check the GitHub repository for the book (read more in the section "Source Code") for continuous updates.

WHAT'S NEW IN C#

Every year, a new version of C# is released, with many new features available in each version. The latest versions include features such as nullable reference types to reduce exceptions of type NullableReferenceException and instead let the compiler help more; features to increase productivity such as indices and ranges; switch expressions that make the switch statement look old; features for using declarations; and enhancements with pattern matching. Top-level statements allow reducing the number of source code lines with small applications and records-classes where the compiler creates boilerplate code for equality comparison, deconstruction, and with expressions. Code generators allow creating code automatically while the compiler runs. All these new features are covered in this book.

WHAT'S NEW IN ASP.NET CORE

ASP.NET Core now contains new technology for creating web applications: Blazor Server and Blazor WebAssembly. With Blazor, you have a full-stack option to write C# code both for the client and for the server. With Blazor Server, the Razor components you create containing HTML and C# code run on the server. With Blazor WebAssembly, Razor components written with C# and HTML run on the client using the HTML 5 standard WebAssembly that allows you to run binary code in the browser, which is supported by all modern web browsers.

For creating services, you can now use gRPC with ASP.NET Core for binary communication between services. This is a great option for service-to-service communication to reduce the bandwidth needed, as well as CPU and memory usage if a lot of data transfer is needed.

WHAT'S NEW WITH WINDOWS

For developing applications for Windows, a new technology combines the features of the Universal Windows Platform and desktop applications: WinUI 3. WinUI is the native UI platform for Windows 10 applications. With WinUI 3, you can use modern XAML code that includes compiled binding to create desktop applications. New controls with Microsoft's fluent design system are available. These controls are not delivered with the Windows Runtime as was previously the case with the Universal Windows Platform (UWP). These controls are developed independently of the Windows 10 version that allows you to use the newest controls with Windows 10 versions 1809 and above. As the roadmap available with WinUI shows, these new controls will be usable from WPF applications as well.

WHAT YOU NEED TO WRITE AND RUN C# CODE

.NET runs on Windows, Linux, and Mac operating systems. You can create and build your programs on any of these operating systems using Visual Studio Code (https://code.visualstudio.com). You can build and run most of the samples on Windows or Linux and use the .NET development tools of your choice. Only the WinUI applications require you to use the Windows platform, and here, Visual Studio is the best option to use. The minimum version required to build and run the WinUI application is version 16.10.

The command line plays an important part when using the .NET CLI and the Azure CLI; you can use the new Windows Terminal. With the newest Windows 10 versions, this...