C# 12 features: ref readonly

Part 3 in a series on new language features in C# 12.

ref readonly modifier

A bit more of a niche feature - if you have code that is passing structs by ref, but you don't need to (or want to) allow modification of the parameter, you can now indicate it is readonly.

    public static void ByRefReadonly(ref readonly Point p)
    {
        //p = new Point(2, 3);
        Console.WriteLine(p);

    }

In the code sample above, Point is a struct or record type. If you uncommented the line then the compiler will emit an error.

Interesting, but I've not come across a need to use this yet.

Further reading

https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/method-parameters?WT.mc_id=DOP-MVP-5001655#ref-readonly-modifier

Example source

https://github.com/flcdrg/csharp-12/blob/main/02-collection-expressions/CollectionExpressions.cs

C# 12 features: Collection expressions

Part 2 in a series on new language features in C# 12.

Collection expressions

You can now use square brackets [] to initialise a collection! Usually square brackets indicate an array, but the collection expression can be assigned to other collection types too.

You can use them to assign values to fields or in method bodies.

private List<int> numbersList = [1, 2, 3, 4, 5];

Like primary constructors, I've also found these quite useful in new .NET 8 projects.

Further reading

https://learn.microsoft.com/dotnet/csharp/language-reference/operators/collection-expressions?WT.mc_id=DOP-MVP-5001655

Example source

https://github.com/flcdrg/csharp-12/blob/main/02-collection-expressions/CollectionExpressions.cs

C# 12 features: Primary constructors

Last month, we had a ".NET 8 Lightning talks" theme for the Adelaide .NET User Group. John covered Blazor, Ryan summarised a bunch of new core library features, and I focused on the 8 new language features added in C# 12. What a great idea for a nice, short blog series!

Primary constructors

C# has had primary constructors for records, but now we can use them for classes and structs!

The parameters can be used anywhere within the class - methods, local functions as well as initialising fields and properties.

A primary constructor guarantees that the named parameters have been supplied when an instance is created. You can optionally add other conventional constructors, but they must all call back to the primary constructor using the this(...) syntax.

public class PrimaryConstructorClass(string name)
{
    private string Name { get; init; } = name;

    private string Name2 => name;

    public void Thing()
    {
        Console.WriteLine(name);
    }
}

I've made regular use of these whenever I've been working on a .NET 8 project. I've found them very useful.

Further reading

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/instance-constructors?WT.mc_id=DOP-MVP-5001655#primary-constructors

Example source

https://github.com/flcdrg/csharp-12/tree/main/01-primary-constructors