[C# 15-Reference]: New Feature - Closed class hierarchies

[BillWagner]

.NET 11 Preview

.NET 11 Preview 5

Link to speclet

• Speclet

Link to Pull request

• PR

New behavior

An abstract class may include the closed modifier. This means that direct derived classes are only allowed in the same assembly. The result is that exhaustiveness can be tracked to that set of derived classes.

Language reference tasks

• A new article should describe the closed modifier.
• Articles on pattern matching exhaustiveness should include a discussion of closed hierarchies.
• Records should also discuss the potential for closed hierarchies.

I'll add a second issue for fundamentals because we don't want to have preview features in fundamentals.

Everyday C# tasks

No response

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Associated WorkItem - 582357