From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 33BA5385DC02; Tue, 22 Mar 2022 20:56:02 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 33BA5385DC02 From: "eyalroz1 at gmx dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/96645] [9/10/11/12 Regression] [CWG2335] std::variant default constructor and unparsed DMI Date: Tue, 22 Mar 2022 20:56:01 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c++ X-Bugzilla-Version: 9.0 X-Bugzilla-Keywords: rejects-valid X-Bugzilla-Severity: normal X-Bugzilla-Who: eyalroz1 at gmx dot com X-Bugzilla-Status: ASSIGNED X-Bugzilla-Resolution: X-Bugzilla-Priority: P2 X-Bugzilla-Assigned-To: jason at gcc dot gnu.org X-Bugzilla-Target-Milestone: 9.5 X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 22 Mar 2022 20:56:02 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96645 --- Comment #18 from Eyal Rozenberg --- (In reply to Jason Merrill from comment #14) > > Alternatively, when not following the standard strictly, why should it = not > > be option (4.): Ignore the official restriction on determining (nothrow) > > constructibility, make a best-effort attempt to determine it anyway ( w= hich > > in this example should succeed), and report failure otherwise. > >=20 > > ? >=20 > If we can define such a best-effort attempt, it could be a candidate for > standardization. Try to resolve is_nothrow_constructible as long as this resolution does = not involve DataWithMember or any of its constituents (e.g. as though we had se= en the initializer expression before the definition of DataWithVariant even began). If that succeeds - we're good; if it fails - that's an error all on its own and we (sort of) don't care about the DataWithVariant error; and if= it trips the wire and tries to refer to DataWithMember or a constituent thereo= f - give up on the parse attempt. Now, this is not _best_ effort, it's actually _minimal_ effort, since we're= not willing to even accept use of A and its constituents, but it's still someth= ing. Not a candidate for standardization though.=