Jaliya Udagedara • 6/25/2026

C# 15.0: Closed Class Hierarchies

This article discusses C# 15.0's closed class hierarchies, a language feature that allows developers to mark a base type with the 'closed' keyword. This ensures the compiler knows all possible derived types within the same assembly, eliminating switch expression exhaustiveness warnings and providing compile-time errors when new subtypes are added but not handled. The post demonstrates the problem with traditional abstract record hierarchies and shows how closed types improve safety and maintainability in pattern matching scenarios.

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#Pattern Matching #Switch Expressions #Net 11