From: Jonathan Wakely <firstname.lastname@example.org>
To: Patrick Palka <email@example.com>
Cc: firstname.lastname@example.org, email@example.com
Subject: Re: [PATCH] libstdc++: Fix backward compatibility of P2325R3 backport [PR106320]
Date: Fri, 22 Jul 2022 17:20:55 +0100 [thread overview]
Message-ID: <CACb0b4=BsWVdyTO-HtaBcOSPF4ODKQ7=yrV5DuHpye1VzM6zqw@mail.gmail.com> (raw)
On Fri, 22 Jul 2022 at 16:52, Patrick Palka via Libstdc++
> The 11 and 10 partial backports of P2325R3, r11-9555-g92d612cccc1eec and
> r10-10808-g22b86cdc4d7fdd, unnecessarily preserved some changes from the
> paper that made certain views no longer default constructible, changes
> which aren't required to reap the overall benefits of the paper and
> which conflicted with the goal to maximize backwards compatibility with
> pre-P2325R3 code.
> This patch reverts the problematic changes, specifically it relaxes
> the constraints on various views' default constructors so that they
> reflect only the requirements that were already implicitly imposed by
> the NSDMIs of the view. Thus for example this patch retains the
> default_initializable<_Vp> constraint on transform_view's default
> constructor since its '_Vp _M_base = _Vp()' NSDMI already reflects this
> constraint, and it removes the default_initializable<_Fp> constraint
> since the corresponding member '__detail::__box<_Fp> _M_fun' doesn't
> require default initializability (specializations of __box are always
> default constructible).
> After reverting these changes, all static_asserts from p2325.cc that
> verify lack of default constructibility now fail as expected, matching
> the pre-P2325R3 behavior.
> Tested on x86_64-pc-linux-gnu, does this look OK for the 11 and 10
OK for gcc-10 and gcc-11 (with the completed ChangeLog), thanks.
prev parent reply other threads:[~2022-07-22 16:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-22 15:52 Patrick Palka
2022-07-22 15:58 ` Patrick Palka
2022-07-22 16:20 ` Jonathan Wakely [this message]
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