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From: "aemseemann at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/109947] std::expected monadic operations do not support move-only error types yet Date: Wed, 24 May 2023 19:34:11 +0000 [thread overview] Message-ID: <bug-109947-4-i3Xb7xqSXk@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-109947-4@http.gcc.gnu.org/bugzilla/> 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.)
next prev parent reply other threads:[~2023-05-24 19:34 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-05-23 19:12 [Bug libstdc++/109947] New: " aemseemann at gmail dot com 2023-05-23 23:32 ` [Bug libstdc++/109947] " redi at gcc dot gnu.org 2023-05-23 23:36 ` redi at gcc dot gnu.org 2023-05-24 19:34 ` aemseemann at gmail dot com [this message] 2023-05-24 20:25 ` redi at gcc dot gnu.org 2023-05-24 21:16 ` aemseemann at gmail dot com 2023-05-25 8:06 ` redi at gcc dot gnu.org 2023-05-25 16:03 ` redi at gcc dot gnu.org 2023-06-01 22:54 ` redi at gcc dot gnu.org 2023-06-06 19:11 ` aemseemann at gmail dot com 2023-06-06 22:59 ` redi at gcc dot gnu.org
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