Discover What’s New in C# 13: Exciting Features and Enhancements

Paweł Majewski — Thu, 24 Apr 2025 12:19:39 +0000

.NET 9 was released on May 21, 2024.

A while ago, we talked about the new features introduced in .NET 8 – a worthy successor to .NET 6?

It hasn’t been long, and we already have .NET 9. Let’s talk about new interesting features.

How to test C# 13 (.NET 9)?

Normally, when we try to build application

We will get an error

Error message error CS8652: The feature 'implicit indexer initializer' is currently in Preview and *unsupported*. To use Preview features, use the 'preview' language version.

Following error message we have to change .csproj file

Original .csproj file



  
    Exe
    net8.0
    enable
    enable

Final version



  
    Exe
    net8.0
    enable
    enable
    Preview

After this modification, the application builds successfully.

Implicit index access

This feature is useful when we are using arrays with a known size.

The code

var test = new Test
{
    Array = {
        [^4] = 0,
        [^2] = 1,
        [^3] = 2,
        [^1] = 3,
    },
    Array2 = {
        [2] = 0,
        [0] = 1,
        [3] = 2,
        [1] = 3,
    }
};

test.Array.ToList().ForEach(x => Console.Write(x));
Console.WriteLine();
test.Array2.ToList().ForEach(x => Console.Write(x));

class Test { 
    public int[] Array = new int[4];
    public int[] Array2 = new int[4];
}

Until now, we could do something like this.

    Array2 = {
        [2] = 0,
        [0] = 1,
        [3] = 2,
        [1] = 3,
    }

But now we are available to do something like this

Array = {
        [^4] = 0,
        [^2] = 1,
        [^3] = 2,
        [^1] = 3,
    }

Python provides elements from the end of a collection by using negative indices (-1, -2, etc.). In C#, we can do the same by using the “^” operator, but until now we weren’t able to use it in initializer expression.

I don’t know of any case where I would use it, but now this limitation is gone.

Enhancements to Extensions

Impossible to test On day 31.05.2024, this feature is still in progress, and it's not implemented in .NET 9.

The code

var square1 = new Square {
    A = 2
};

Console.WriteLine(square1.CalculateArea());
Console.WriteLine(square1.CalculateDiagonal());

class Square { 
    public int A { get; set; }
}

static class TestExtensions {
    public static int CalculateArea(this Square square) {
        return square.A * square.A;
    }

    public static double CalculateDiagonal(this Square square) {
        return square.A * Math.Sqrt(2);
    }
}

Above is a simple example of existing extensions. What improvements can we make in .NET 9 and C# 13?

The CalculateArea method is good, and we have nothing to change here.

The CalculateDiagonal method would be clearer and more intuitive if it were a property, not a method. With C# 13 we can do that!

The code

var square1 = new Square {
    A = 2
};

Console.WriteLine(square1.CalculateArea());
Console.WriteLine(square1.CalculateDiagonal());
Console.WriteLine(square1.Diagonal);

public class Square 
{ 
    public int A { get; set; }
}

public implicit extension SquareExtensions for Square
{
    public double Diagonal => this.A * Math.Sqrt(2);
}

static class TestExtensions 
{
    public static int CalculateArea(this Square square) {
        return square.A * square.A;
    }

    public static double CalculateDiagonal(this Square square) {
        return square.A * Math.Sqrt(2);
    }
}

This part of code extends the Square class with an attribute called Diagonal. What’s interesting is that we can extend everything, even types not owned (for example, from NuGet packages).

public implicit extension SquareExtensions for Square
{
    public double Diagonal => this.A * Math.Sqrt(2);
}

You can track the progress on Language Feature Status.

You can read more about C# 13 at: https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13

The post Discover What’s New in C# 13: Exciting Features and Enhancements first appeared on Software Developer's Tour.

.NET 8 – a worthy successor to .NET 6?

Paweł Majewski — Sun, 05 Jan 2025 07:00:00 +0000

Hi!

Today, I’d like to discuss the news about .NET 8. As you may know, .NET 6 will reach the end of support on November 12, 2024, and the next LTS version will be .NET 8.

What is the best feature in C# 12?

For me, the absolute best feature is definitely the one called “Collection Expressions”.

In C#, the syntax for creating arrays has been made similar to that of Python or JavaScript.

Take a look at the syntax below.

As you can see, there’s no need to use new keyword before array initialization.

When is it useable in real code?

The second option seems better, doesn’t it?

Rule for your IDE (IDE0300)

This rule prefers new syntax and IDE will show you probably well known light bulb suggestions.

You can read more about it on

Use collection expression for array (IDE0300)

What other interesting changes are there?

I want to talk about breaking changes between .NET 6 and .NET 7.

First, the code

It looks very complicated, but after spending some time, it looks easy. The title of this is

Previously, when we executed the M method with the ref i argument as M(ref i), the first matched method was the extension method with the ref int i parameter in line 11.

Now in .NET 8 we are allowed to pass ref arguments to function with in parameters. That means when we execute M(ref i) the first matched method will be instance method in class C.

Why do I consider this change to be rather significant?

I believe that changing the outcome of previously written code is very risky. While this is an extreme case for the problem being described here, if the functionality relying on the above scheme hasn’t had tests written for it, the application’s behavior may become unpredictable in certain cases.

Is that all?

Of course not, C# 12 introduces more interesting things like FrozenDictionary or FrozenHashSet and more, but that’s for another time.

Want to know more?

Visit What’s new in C# 12

The post .NET 8 – a worthy successor to .NET 6? first appeared on Software Developer's Tour.

.NET - Software Developer's Tour

Discover What’s New in C# 13: Exciting Features and Enhancements

.NET 9 was released on May 21, 2024.

How to test C# 13 (.NET 9)?

Implicit index access

Enhancements to Extensions

.NET 8 – a worthy successor to .NET 6?

What is the best feature in C# 12?

Rule for your IDE (IDE0300)

What other interesting changes are there?

Is that all?

Want to know more?