type matching, they talk about 4 cases but aren't the 2nd and the 3rd identical?

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original issue description:

They say there are 4 cases for type pattern matching. But the second and the third seem to me to be identical:

2. expr is an instance of a type that derives from type. In other words, the result of expr can be upcast to an instance of type.

3. expr has a compile-time type that is a base class of type, and expr has a runtime type that is type or is derived from type. The compile-time type of a variable is the variable's type as defined in its declaration. The runtime type of a variable is the type of the instance that is assigned to that variable.

Am I missing something? If there is a very subtle difference, focus should be put on it because this way it's very difficult to spot it.

---

Document Details

⚠ Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.

• ID: 3126aaa9-8f5f-04f3-2d75-96477b6273cd
• Version Independent ID: 3f4b3eac-11eb-2dd6-4f27-b24537367288
• Content: is - C# Reference
• Content Source: docs/csharp/language-reference/keywords/is.md
• Product: dotnet-csharp
• Technology: csharp-language-reference
• GitHub Login: @BillWagner
• Microsoft Alias: wiwagn

Fixes #22163.

---

💬 Share your feedback on Copilot coding agent for the chance to win a $200 gift card! Click here to start the survey.

---

Internal previews

📄 File	🔗 Preview link
docs/csharp/language-reference/operators/patterns.md	docs/csharp/language-reference/operators/patterns
docs/csharp/language-reference/operators/type-testing-and-cast.md	docs/csharp/language-reference/operators/type-testing-and-cast

[BillWagner]

Hi @copilot Can you start working on this again?

[Copilot]

Hi @copilot Can you start working on this again?

I'll start working on this issue. Looking at the current documentation for type pattern matching, I can see the conditions that might be causing confusion. Let me analyze the current state and identify areas that need clarification.

[BillWagner]

Just a couple small changes, and then this is ready.

[BillWagner]

This is ready for final review.