What's new in csharp 9.0?
Quick collection of examples of what's new in C# 9.0. Also, you should check out the what's new guide by Microsoft.
But first, how do I get this thing?
Downloads for different platforms are available at dotnet.microsoft.com/download/dotnet/5.0.
Top-level programs
Whish C# was more like a scripting language? Not so much ceremony? Now you can have it! Try running "TopLevel":
$ TopLevel> dotnet run -- 10
The sum of all the multiples of 3 or 5 below 10 is 23Some things to note:
- Stuff all using statements at the top.
- Only do this in one file. The rest has to be done as usual.
- Please return a status code if you want.
- args will magically be available.
- Yeah, await works as well.
Where could this be useful?
- When writing short scripts
- When working on batch jobs
Init only setters
A lot of times you have properties on objects that should not be changed after the object is created. Traditionally this require a lot of work with readonly and constructors. Init only setters makes this easier.
Have a look at the example is "InitProperties". Status.Name should not be changed. Here we could use an init only setter to avoid the problem.
Where could this be useful?
- When you have select properties that should not change. Maybe ID-properties?
- Would probably use record more?
Records
Sometimes all properties on an object should not be mutable. This is where records shine. In addition they come with built in equality by properties. Have a look at "Records" to see some examples of how records can be used.
Where could this be useful?
- All over the place in domain models.
- How will they work with libraries and frameworks?
Pattern matching
Have a look at the pattern matching enhancements section in the what's new in C# 9.0 article from Microsoft.
The "PatternMatching" project includes some examples, with and without switch expressions.
Where could this be useful?
- Would probably implement some stuff as methods on different sub-objects.
- When working on complex logic.