C# 10: New features and examples that are not in C# 9

// Framework.cs
namespace RoundTheCode.CSharp10.Models {
	public class Framework
	{
		public string? Name { get; set; }

		public int Version { get; set; }

		public CodingLanguage? CodingLanguage { get; set; }
	}
}

This would mean that the contents within the namespace would be indented to the right.

However, with C#10, you can now declare a file scoped namespace at the top of the file. As a result, every object within that file will belong to that namespace.

// Framework.cs
namespace RoundTheCode.CSharp10.Models;
 
public class Framework
{
	public string? Name { get; set; }

	public int Version { get; set; }

	public CodingLanguage? CodingLanguage { get; set; }
}

The benefits of having a file scoped namespace is that you are reducing horizontal waste and it looks cleaner and tidier.

Feature #2: Record structs

C# 9 saw the introduction of record classes.

C# 10 takes the record keyword further, so you can now declare a struct as a record.

One of the benefits with record classes is that they can be immutable. Below is an example of how to declare an immutable struct record, and how to initialise it.

// Framework.cs
public readonly record struct Framework(string? Name, int Version, CodingLanguage? CodingLanguage);

// CodingLanguage.cs
public readonly record struct CodingLanguage (string? Name);

// FrameworkController.cs
[Route("framework")]
public class FrameworkController : Controller
{
	[HttpGet("record-structs")]
	public IActionResult RecordStructs()
	{
		var framework = new Framework
		{
			Name = ".NET",
			Version = 6,
			CodingLanguage = new CodingLanguage { Name = "C#" }
		};

		return Json(framework);
	}
}

There is no need to declare properties in a readonly record struct. Simply pass in the property names as constructors, and it will automatic bind the property names and their values to that struct.

Feature #3: Constant interpolated strings

Interpolated strings come in handy as it means you can add an object to a string without coming out of the string.

Before C# 10, interpolated strings were perfectly acceptable when declared as a var:

var languageReleasePrefix = "C# 10";
var languageRelease = $"{languageReleasePrefix} to be released in November 2021.";
 
return Json(languageRelease);

However, if you change the personString to a const, it would throw an error.

But that's not the case with C# 10. You can now declare a interpolated string as a constant.

const string languageReleasePrefix = "C# 10";
const string languageRelease = $"{languageReleasePrefix} to be released in November 2021.";
 
return Json(languageRelease);

Feature #4: Extended property patterns

Extended property patterns makes it cleaner to do a condition on a nested property.

Take this switch example. In C# 9, you would have to wrap nested properties in curly braces:

public static string GetFullCodingLanguageName(Framework framework) => framework switch
{
	{ CodingLanguage: { Name: "C#" } } => "C Sharp",
	_ => "(unknown)"
};

But in C# 10, you now declare nested properties using a dot.

public static string GetFullCodingLanguageName(Framework framework) => framework switch
{
	{ CodingLanguage.Name: "C#" } => "C Sharp",
	_ => "(unknown)"
};

Feature #5: Global using directive

Don't you just hate having to import the same namespaces multiple times for different classes?

Well in C# 10, there is a new global keyword that allows you to declare your common namespaces in your application.

It is recommended that you create a separate file to store your global namespaces. We have created a GlobalUsing.cs file and this how it looks:

// GlobalUsing.cs
global using Microsoft.AspNetCore.Mvc;
global using RoundTheCode.CSharp10.Models;

This now means that we no longer have to declare these namespaces in each individual file.

See these new C# 10 features in action

Check out our YouTube feature where we demonstrate these features in action: