C# 13 and .NET 9: What's New - C# language

This article is about the new features in the C# 13 language. To use the C# 13 compiler you must install .NET SDK 9. You can continue to target .NET 8 in your projects for long-term support.

Extension Types postponed

Sadly, the biggest new feature planned for C# 13, Extension Types, was postponed. You can read more about this future feature at the following link:

https://devblogs.microsoft.com/dotnet/csharp-13-explore-preview-features/#update-on-extension-types

C# 13 new features: params, \e, and partial properties

Three refinements in C# 13 that provide more flexibility and simplicity are:

• The params modifier can now use any recognized collection type, it is no longer limited to array types. For example, it can be used on System.Span<T> and types that implement IEnumerable<T> and have an Add method. You can learn more at the following link: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-13.0/params-collections.
• You can now use \e as a character literal escape sequence for the ESCAPE character as well as Unicode U+001B.
• C# has supported the partial modifier on methods since C# 3 in 2007. C# 13 finally extends that support to partial properties and indexers. You can learn more about partial members at the following link: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/partial-member.

Exceptions are now 2-4x faster. This benefit does not require any changes to your code so you get the benefits automatically.

You can read the official list of all new features at the following link: What's new in C# 13

Summary

C# 13 and .NET 9 add many other new features. Learn about them in the latest edition of my book, C# 13 and .NET 9 - Modern Cross-Platform Development Fundamentals, coming on November 12, 2024. https://www.amazon.com/13-NET-Cross-Platform-Development-Fundamentals/dp/183588122X/

Microsoft will release .NET 9 at .NET Conf 2024. https://www.dotnetconf.net/