Update anonymous types article to cover tuples as preferred alternative

[Copilot]

The anonymous types article was outdated and didn't address tuples, which are the preferred choice in modern C# for most scenarios where anonymous types were traditionally used.

Changes

• Added prominent TIP callout recommending tuples as the preferred choice with clear guidance on when to use each type
• New comparison section with table contrasting anonymous types vs tuples across key dimensions: type (reference/value), performance (heap/stack), mutability, deconstruction support, expression tree support, access modifiers, and member naming
• When to use guidance for both types with specific scenarios
• Code example demonstrating tuple equivalence to anonymous types with deconstruction
• See also section linking to tuple types reference and "Choosing between anonymous and tuple types" article

Example

The article now includes practical comparison:

// Anonymous type example
var anonymousProduct = new { Name = "Widget", Price = 19.99M };
Console.WriteLine($"Anonymous: {anonymousProduct.Name} costs ${anonymousProduct.Price}");

// Equivalent using tuple with named elements
var tupleProduct = (Name: "Widget", Price: 19.99M);
Console.WriteLine($"Tuple: {tupleProduct.Name} costs ${tupleProduct.Price}");

// Tuples support deconstruction
var (productName, productPrice) = tupleProduct;
Console.WriteLine($"Deconstructed: {productName} costs ${productPrice}");

The article maintains coverage of anonymous types while clearly establishing tuples as the modern default choice.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Update Anonymous types article to cover tuples</issue_title>
<issue_description>### Type of issue

Outdated article

Description

Tuples server a similar purpose to anonymous types but have better language support and compile to a more efficient data structure.

Update the Anonymous types article to focus on tuples. Include the differences between the two, and why it's preferred to use tuples.

Page URL

https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/types/anonymous-types

Content source URL

https://github.com/dotnet/docs/blob/main/docs/csharp/fundamentals/types/anonymous-types.md

Document Version Independent Id

dd937177-98f0-a797-d49b-29332aae0614

Platform Id

ecfed45c-63aa-17f6-2cfc-88b1f8bc7adb

Article author

@BillWagner

Metadata

• ID: d1b30ebe-b640-449b-3602-9891a55794db
• PlatformId: ecfed45c-63aa-17f6-2cfc-88b1f8bc7adb
• Service: dotnet-csharp
• Sub-service: fundamentals

Related Issues</issue_description>

<agent_instructions>The anonymous types article should include more details about tuples. Refer to: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/value-tuples and https://learn.microsoft.com/en-us/dotnet/standard/base-types/choosing-between-anonymous-and-tuple for more details. Also link to: https://learn.microsoft.com/en-us/dotnet/standard/base-types/choosing-between-anonymous-and-tuple as related content.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Update Anonymous types article to cover tuples #49291

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Internal previews

📄 File	🔗 Preview link
docs/csharp/fundamentals/types/anonymous-types.md	Anonymous types and tuples
docs/csharp/toc.yml	Taken from https://github.com/dotnet/roslyn/wiki/Samples-and-Walkthroughs