https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109947
--- Comment #3 from Martin Seemann <aemseemann at gmail dot com> --- Thanks for pointing me to the LWG issue. It makes sense that the error type must be copyable for the `value()` overloads due to potentially throwing a `bad_expected_access` with the embedded error embedded. However, the monadic operations will never throw this exception. Consequently, the standard draft for the monadic operations (https://eel.is/c++draft/expected.object.monadic) does not contain any "Throws:" clause nor is copyability of the error type included in the "Constraints:" clause. So it comes down to how to interpret the "Effects:" clause: Does "Equivalent to <statements involving std::move(value())>" mean that all restrictions of `value()` apply transitively or is it merely an implementation hint? (Strangely enough, in the "Effects:" clause of `value_or()&&` the expression `std::move(**this)` is used instead of `std::move(value())`. Maybe this is an oversight/inconsistency of the standard.)
