What's new in C# 9.0

Presentation from .NET Conf Thailand 2020

See the stream here: https://www.youtube.com/watch?v=-iQkrvBBcTA

Contents

• What's new in C# 9.0.pdf - slides (only two) from the presentation.
• What's new in C#.ipynb - Jupyter notebook of new C# 9.0 features (uses dotnet interactive).
• HelloWorld - A visual studio solution used during the presentation.

References

• https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-9
• https://devblogs.microsoft.com/dotnet/introducing-c-source-generators/

Questions

• I heard will soon have record class and record struct?
  • Maybe! In C# 9, we just have record which means record class. In future versions of C# (e.g. 10) we might get new record class and record struct syntax; and record would continue to be a shorthand for record class.
• Do we get C# 9 automatically when we create a .Net 5.0 project or do we need to do something else?
  • Yes! We get C# 9 automatically when we create a .NET 5.0 project.
• Is Customer == null equal to Customer is null? Which one executes quicker?
  • They're not quite equal. If Customer implements an operator overload for equality, Customer == null will call that overload. The pattern matching approach, Customer is null, is guaranteed to do a real null check, regardless of any operator overload.
  • For this reason, since C# 7, the recommended way to null checks is to use Customer is null. In the absence of overloads, the performance is identical