Add naming conventions for primary constructor parameters (#48009)

* Initial plan

* Add naming rules for primary constructor parameters

Co-authored-by: BillWagner <[email protected]>

* Apply suggestions from code review

* Apply suggestions from code review

Co-authored-by: Genevieve Warren <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: BillWagner <[email protected]>
Co-authored-by: Bill Wagner <[email protected]>
Co-authored-by: Genevieve Warren <[email protected]>

Author: 3 people

docs/csharp/fundamentals/coding-style/identifier-names.md

@@ -2,6 +2,7 @@
 title: "Identifier names - rules and conventions"
 description: "Learn the rules for valid identifier names in the C# programming language. In addition, learn the common naming conventions used by the .NET runtime team and the .NET docs team."
 ms.date: 11/27/2023
+ai-usage: ai-assisted
 ---
 # C# identifier naming rules and conventions
 
@@ -159,6 +160,22 @@ public T SomeMethod<T>(int someNumber, bool isValid)
 }
 ```
 
+#### Primary constructor parameters
+
+How you name primary constructor parameters depends on the type being declared:
+
+- For `class` and `struct` types: Use camel casing, consistent with other method parameters.
+
+  :::code language="csharp" source="./snippets/identifier-names/PrimaryConstructorExamples.cs" id="ClassPrimaryConstructor":::
+
+  :::code language="csharp" source="./snippets/identifier-names/PrimaryConstructorExamples.cs" id="StructPrimaryConstructor":::
+
+- For `record` types: Use Pascal casing, as the parameters become public properties.
+
+  :::code language="csharp" source="./snippets/identifier-names/PrimaryConstructorExamples.cs" id="RecordPrimaryConstructor":::
+
+For more information on primary constructors, see [Primary constructors](../../programming-guide/classes-and-structs/instance-constructors.md#primary-constructors).
+
 For more information on C# naming conventions, see the [.NET Runtime team's coding style](https://github.com/dotnet/runtime/blob/main/docs/coding-guidelines/coding-style.md).
 
 ### Type parameter naming guidelines

docs/csharp/fundamentals/coding-style/snippets/identifier-names/PrimaryConstructorExamples.cs

@@ -0,0 +1,48 @@
+using System;
+using Microsoft.Extensions.Logging;
+
+namespace IdentifierNamingExamples;
+
+// <ClassPrimaryConstructor>
+public class DataService(IWorkerQueue workerQueue, ILogger logger)
+{
+    public void ProcessData()
+    {
+        // Use the parameters directly
+        logger.LogInformation("Processing data");
+        workerQueue.Enqueue("data");
+    }
+}
+// </ClassPrimaryConstructor>
+
+// <StructPrimaryConstructor>
+public struct Point(double x, double y)
+{
+    public double Distance => Math.Sqrt(x * x + y * y);
+}
+// </StructPrimaryConstructor>
+
+// <RecordPrimaryConstructor>
+public record Person(string FirstName, string LastName);
+public record Address(string Street, string City, string PostalCode);
+// </RecordPrimaryConstructor>
+
+// Supporting interfaces for examples
+public interface IWorkerQueue
+{
+    void Enqueue(string item);
+    int Count { get; }
+}
+
+// Add a simple main method to make it an executable
+public class Program
+{
+    public static void Main()
+    {
+        // Example usage
+        var person = new Person("John", "Doe");
+        var address = new Address("123 Main St", "Anytown", "12345");
+        Console.WriteLine($"{person.FirstName} {person.LastName}");
+        Console.WriteLine($"{address.Street}, {address.City} {address.PostalCode}");
+    }
+}

docs/csharp/fundamentals/coding-style/snippets/identifier-names/identifier-names.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <RootNamespace>IdentifierNamingExamples</RootNamespace>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Logging" Version="8.0.0" />
+  </ItemGroup>
+
+</Project>