LDM Notes for April 20th, 2026

[333fred]

https://github.com/dotnet/csharplang/blob/main/meetings/2026/LDM-2026-04-20.md

Agenda

• Closed hierarchies continued
  • Generics and exhaustiveness
  • Accessibility and exhaustiveness
  • Interface convertibility of sealed classes
  • Concrete intermediate nodes

[BreyerW]

Is it impossible for Roslyn to calculate new set of subtypes for exhaustiveness based on accessibility in the given context? It looks like a shame to lose proper exhaustiveness outside of declaration as soon as you introduce even a single private leaf

[jnm2]

Well, it's not exhaustive if that private leaf instance could get passed around to that other context. Nothing necessarily rules out having that leaf instance get passed to a place where it can't be named.

[BreyerW]

ah yeah fair enough but also a bit of a bummer