C# 9.0 New Features

Happy New Year y'all!

C# 9.0 was released to GA along with .NET 5 November 2020. It adds a number of new features to the language the biggest of which is records.

Records provide a way to quickly define classes that are essentially property bags. By default, they come with value semantics (opposed to reference semantics) and additional behaviour like equality and immutability for free. Previously, you would have to implement these behaviours manually. For any small value-based types (e.g. classes used for JSON serialisation), ask yourself if this is just a collection of values. If so, you may consider moving them to records. Also, considering records can be defined in a single line, you may want to re-consider the standard rule of one file per type. 😉

Sometimes we write classes with constructors and with read-only to give us immutability. Now to achieve the same thing we can use init-only properties instead.

Source Code Generators use Roslyn APIs to add new source code to be compiled into the program. They cannot modify existing source code.

The full list of features included in C# 9.0 is:

Records
Init only setters
Top-level statements
Pattern matching enhancements
Native sized integers
Function pointers
Suppress emitting localsinit flag
Target-typed new expressions
static anonymous functions
Target-typed conditional expressions
Covariant return types
Extension GetEnumerator support for foreach loops
Lambda discard parameters
Attributes on local functions
Module initializers
New features for partial methods

I have included examples of most of these on Git Hub

Code

The code for this article can be found on Git Hub

Code

Resources