[libcxx-commits] [libcxx] [libc++] Mark std::expected as nodiscard (PR #139651)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 requested changes to this pull request.

The general consensus was that we want a way for users to allow discarding `expected` on a per-function basis.

https://github.com/llvm/llvm-project/pull/139651