Create tutorial for C# 14 extension members #48896

BillWagner · 2025-10-03T21:14:54Z

Create a tutorial to explore C# 14 extension members.

Internal previews

📄 File	🔗 Preview link
docs/csharp/toc.yml	Taken from https://github.com/dotnet/roslyn/wiki/Samples-and-Walkthroughs
docs/csharp/whats-new/tutorials/extension-members.md	Explore extension members in C# 14 to enhance existing types

BillWagner · 2025-10-06T18:48:51Z

Tagging @adegeo because he gave me some ideas for extensions

Copilot

Pull Request Overview

This PR creates a comprehensive tutorial for C# 14 extension members, a new language feature that enhances the existing extension methods functionality by enabling properties, operators, and type-level extensions.

Key Changes:

Added a new tutorial demonstrating extension members syntax and capabilities
Created supporting code samples comparing traditional extension methods with new extension member features
Updated the table of contents to include the new tutorial

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

File	Description
docs/csharp/whats-new/tutorials/extension-members.md	Main tutorial document explaining extension members concepts and syntax
docs/csharp/toc.yml	Added navigation entry for the new extension members tutorial
docs/csharp/whats-new/tutorials/snippets/PointExtensions/*.cs	Code samples demonstrating both traditional extension methods and new extension members

Copilot · 2025-10-06T18:49:11Z

docs/csharp/whats-new/tutorials/extension-members.md

@@ -0,0 +1,190 @@
+---
+title: Explore extension members in C# 14 to enhance existing types
+description: "C# 14 enables provides new syntax for extensions that support properties and operators, and enables extensions on a type as well as an instance. Learn to use them, and how to migrate existing extension methods to extension members"


Corrected grammatical error 'enables provides' to 'enables' or 'provides'.

Suggested change

description: "C# 14 enables provides new syntax for extensions that support properties and operators, and enables extensions on a type as well as an instance. Learn to use them, and how to migrate existing extension methods to extension members"

description: "C# 14 provides new syntax for extensions that support properties and operators, and enables extensions on a type as well as an instance. Learn to use them, and how to migrate existing extension methods to extension members"

Copilot · 2025-10-06T18:49:12Z

docs/csharp/whats-new/tutorials/extension-members.md

+ms.topic: tutorial
+ms.date: 10/06/2025
+ai-usage: ai-assisted
+#customer intent: As a C# developer, I reduce repeated code by introducting extension members for common tasks 


Corrected spelling of 'introducting' to 'introducing'.

Suggested change

#customer intent: As a C# developer, I reduce repeated code by introducting extension members for common tasks

#customer intent: As a C# developer, I reduce repeated code by introducing extension members for common tasks

Copilot · 2025-10-06T18:49:12Z

docs/csharp/whats-new/tutorials/extension-members.md

+   cd PointExtensions
+   ```
+
+1. Copy the following code into a new filed named `ExtensionMethods.cs`:


Corrected spelling of 'filed' to 'file'.

Suggested change

1. Copy the following code into a new filed named `ExtensionMethods.cs`:

1. Copy the following code into a new file named `ExtensionMethods.cs`:

Copilot · 2025-10-06T18:49:12Z

docs/csharp/whats-new/tutorials/snippets/PointExtensions/NewExtensionsMembers.cs

+        public void Rotate(int angleInDegress)
+        {
+            double theta = ((double)angleInDegress * Math.PI) / 180.0;


Corrected spelling of 'angleInDegress' to 'angleInDegrees'.

Suggested change

public void Rotate(int angleInDegress)

{

double theta = ((double)angleInDegress * Math.PI) / 180.0;

public void Rotate(int angleInDegrees)

{

double theta = ((double)angleInDegrees * Math.PI) / 180.0;

Copilot · 2025-10-06T18:49:12Z

docs/csharp/whats-new/tutorials/snippets/PointExtensions/ExtensionMethods.cs

+    public static void Rotate(this Point point, int angleInDegress)
+    {
+        double theta = ((double)angleInDegress * Math.PI) / 180.0;


Corrected spelling of 'angleInDegress' to 'angleInDegrees'.

Suggested change

public static void Rotate(this Point point, int angleInDegress)

{

double theta = ((double)angleInDegress * Math.PI) / 180.0;

public static void Rotate(this Point point, int angleInDegrees)

{

double theta = ((double)angleInDegrees * Math.PI) / 180.0;

meaghanlewis

Great tutorial @BillWagner! I left primarily style changes for you to consider.

meaghanlewis · 2025-10-06T21:05:05Z

docs/csharp/whats-new/tutorials/extension-members.md

+
+The extension operators make point arithmetic as natural as working with built-in numeric types.
+
+## Add More operators


Suggested change

## Add More operators

## Add more operators

meaghanlewis · 2025-10-06T21:29:11Z

docs/csharp/whats-new/tutorials/extension-members.md

+
+## Migrate instance methods to extension members
+
+Extension members also support instance methods. You don't have to change existing extension methods. The old and new forms are binary and source compatible. If you want to keep all your extensions in one container, you can. Migrate traditional extension methods to the new syntax maintains the same functionality.


Suggested change

Extension members also support instance methods. You don't have to change existing extension methods. The old and new forms are binary and source compatible. If you want to keep all your extensions in one container, you can. Migrate traditional extension methods to the new syntax maintains the same functionality.

Extension members also support instance methods. You don't have to change existing extension methods. The old and new forms are binary and source compatible. If you want to keep all your extensions in one container, you can. Migrating traditional extension methods to the new syntax maintains the same functionality.

meaghanlewis · 2025-10-06T21:34:18Z

docs/csharp/whats-new/tutorials/extension-members.md

+
+## Related content
+
+* [Extension methods (C# Programming Guide)](/dotnet/csharp/programming-guide/classes-and-structs/extension-methods)


Suggested change

* [Extension methods (C# Programming Guide)](/dotnet/csharp/programming-guide/classes-and-structs/extension-methods)

- [Extension methods (C# Programming Guide)](/dotnet/csharp/programming-guide/classes-and-structs/extension-methods)

meaghanlewis · 2025-10-06T21:34:28Z

docs/csharp/whats-new/tutorials/extension-members.md

+## Related content
+
+* [Extension methods (C# Programming Guide)](/dotnet/csharp/programming-guide/classes-and-structs/extension-methods)
+* [What's new in C# 14](/dotnet/csharp/whats-new/csharp-14)


Suggested change

* [What's new in C# 14](/dotnet/csharp/whats-new/csharp-14)

- [What's new in C# 14](/dotnet/csharp/whats-new/csharp-14)

meaghanlewis · 2025-10-06T21:34:36Z

docs/csharp/whats-new/tutorials/extension-members.md

+
+* [Extension methods (C# Programming Guide)](/dotnet/csharp/programming-guide/classes-and-structs/extension-methods)
+* [What's new in C# 14](/dotnet/csharp/whats-new/csharp-14)
+* [Operator overloading (C# reference)](/dotnet/csharp/language-reference/operators/operator-overloading)


Suggested change

* [Operator overloading (C# reference)](/dotnet/csharp/language-reference/operators/operator-overloading)

- [Operator overloading (C# reference)](/dotnet/csharp/language-reference/operators/operator-overloading)

meaghanlewis · 2025-10-06T21:41:12Z

docs/csharp/whats-new/tutorials/snippets/PointExtensions/ExtensionMethodsDemonstrations.cs

+        Point rotatePoint2 = new Point(5, 5);
+        Console.WriteLine($"Before Rotate: {rotatePoint2}");
+        rotatePoint2.Rotate(45);
+        Console.WriteLine($"After Rotate(45�): {rotatePoint2}");


Suggested change

Console.WriteLine($"After Rotate(45�): {rotatePoint2}");

Console.WriteLine($"After Rotate(45°): {rotatePoint2}");

meaghanlewis · 2025-10-06T21:41:20Z

docs/csharp/whats-new/tutorials/snippets/PointExtensions/ExtensionMethodsDemonstrations.cs

+        Point rotatePoint3 = new Point(3, 4);
+        Console.WriteLine($"Before Rotate: {rotatePoint3}");
+        rotatePoint3.Rotate(180);
+        Console.WriteLine($"After Rotate(180�): {rotatePoint3}");


Suggested change

Console.WriteLine($"After Rotate(180�): {rotatePoint3}");

Console.WriteLine($"After Rotate(180°): {rotatePoint3}");

meaghanlewis · 2025-10-06T21:41:38Z

docs/csharp/whats-new/tutorials/snippets/PointExtensions/IncludedElements.cs

+        Point rotatePoint1 = new Point(10, 0);
+        Console.WriteLine($"Before Rotate: {rotatePoint1}");
+        rotatePoint1.Rotate(90);
+        Console.WriteLine($"After Rotate(90�): {rotatePoint1}");


Suggested change

Console.WriteLine($"After Rotate(90�): {rotatePoint1}");

Console.WriteLine($"After Rotate(90°): {rotatePoint1}");

meaghanlewis · 2025-10-06T21:41:48Z

docs/csharp/whats-new/tutorials/snippets/PointExtensions/IncludedElements.cs

+        Point rotatePoint2 = new Point(5, 5);
+        Console.WriteLine($"Before Rotate: {rotatePoint2}");
+        rotatePoint2.Rotate(45);
+        Console.WriteLine($"After Rotate(45�): {rotatePoint2}");


Suggested change

Console.WriteLine($"After Rotate(45�): {rotatePoint2}");

Console.WriteLine($"After Rotate(45°): {rotatePoint2}");

meaghanlewis · 2025-10-06T21:41:58Z

docs/csharp/whats-new/tutorials/snippets/PointExtensions/IncludedElements.cs

+        Point rotatePoint3 = new Point(3, 4);
+        Console.WriteLine($"Before Rotate: {rotatePoint3}");
+        rotatePoint3.Rotate(180);
+        Console.WriteLine($"After Rotate(180�): {rotatePoint3}");


Suggested change

Console.WriteLine($"After Rotate(180�): {rotatePoint3}");

Console.WriteLine($"After Rotate(180°): {rotatePoint3}");

Rough draft

5a968ec

dotnetrepoman bot added this to the October 2025 milestone Oct 3, 2025

dotnet-policy-service bot added dotnet-csharp/svc whats-new/subsvc labels Oct 3, 2025

BillWagner added 4 commits October 3, 2025 17:22

build warnings

07d5f59

typo

400c3a7

Improve sample organization

6965d7f

proofread

a0f30a1

BillWagner marked this pull request as ready for review October 6, 2025 18:48

BillWagner requested a review from a team as a code owner October 6, 2025 18:48

BillWagner requested review from Copilot, IEvangelist and adegeo October 6, 2025 18:48

Copilot AI reviewed Oct 6, 2025

View reviewed changes

meaghanlewis approved these changes Oct 6, 2025

View reviewed changes

	description: "C# 14 enables provides new syntax for extensions that support properties and operators, and enables extensions on a type as well as an instance. Learn to use them, and how to migrate existing extension methods to extension members"
	description: "C# 14 provides new syntax for extensions that support properties and operators, and enables extensions on a type as well as an instance. Learn to use them, and how to migrate existing extension methods to extension members"

	#customer intent: As a C# developer, I reduce repeated code by introducting extension members for common tasks
	#customer intent: As a C# developer, I reduce repeated code by introducing extension members for common tasks

	1. Copy the following code into a new filed named `ExtensionMethods.cs`:
	1. Copy the following code into a new file named `ExtensionMethods.cs`:


		The extension operators make point arithmetic as natural as working with built-in numeric types.

		## Add More operators


		## Migrate instance methods to extension members

		Extension members also support instance methods. You don't have to change existing extension methods. The old and new forms are binary and source compatible. If you want to keep all your extensions in one container, you can. Migrate traditional extension methods to the new syntax maintains the same functionality.


		## Related content

		* [Extension methods (C# Programming Guide)](/dotnet/csharp/programming-guide/classes-and-structs/extension-methods)

	* [Extension methods (C# Programming Guide)](/dotnet/csharp/programming-guide/classes-and-structs/extension-methods)
	- [Extension methods (C# Programming Guide)](/dotnet/csharp/programming-guide/classes-and-structs/extension-methods)

	* [What's new in C# 14](/dotnet/csharp/whats-new/csharp-14)
	- [What's new in C# 14](/dotnet/csharp/whats-new/csharp-14)

	* [Operator overloading (C# reference)](/dotnet/csharp/language-reference/operators/operator-overloading)
	- [Operator overloading (C# reference)](/dotnet/csharp/language-reference/operators/operator-overloading)

	Console.WriteLine($"After Rotate(45�): {rotatePoint2}");
	Console.WriteLine($"After Rotate(45°): {rotatePoint2}");

	Console.WriteLine($"After Rotate(180�): {rotatePoint3}");
	Console.WriteLine($"After Rotate(180°): {rotatePoint3}");

	Console.WriteLine($"After Rotate(90�): {rotatePoint1}");
	Console.WriteLine($"After Rotate(90°): {rotatePoint1}");

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Pull Request Overview

Key Changes:

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BillWagner commented Oct 3, 2025 •

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