C# 15 Language Features in Practice

C# 15 is still taking shape in preview. This tag collects a critical look at the candidate and preview-stage language features headed toward it: closed hierarchies, union types, and whatever else lands before general availability, evaluated for what they genuinely solve versus what they merely rebrand from other languages.

C# 15 Union Types and Closed Hierarchies in Preview

C# 15 preview ships union types with real compiler-checked exhaustiveness, no more hand-rolled sealed hierarchies for a Result type. The catch: it is a union of pre-existing types, not F#-style discriminated cases, and value-type cases box unless you write non-boxing boilerplate yourself. The quieter sibling feature, closed hierarchies, may be the safer bet for enterprise teams right now.