public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/98978] Consider packing _M_Engaged in the tail padding of T in optional<>
Date: Sat, 06 Feb 2021 17:26:52 +0000	[thread overview]
Message-ID: <bug-98978-4-mLvt4x2V0u@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-98978-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98978

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to andysem from comment #3)
> Is there no way to improve standard components implementation? I'd imagine
> you could provide the new implementation in the new version inline namespace
> and still support the old ABI for backward compatibility.

Yes ABI changes can be done for the --enable-symvers=gnu-versioned-namespace
configuration, but nobody uses it so anything invasive like this is not worth
the effort.

> This would be more problematic as emplace(), value() and operator*() need to
> return T&, which would not be possible.

Use 0xff to mean disengaged, and 0x00 and 0x01 for engaged. You only need to
return a reference when it's engaged.

  parent reply	other threads:[~2021-02-06 17:26 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-05 17:14 [Bug libstdc++/98978] New: " andysem at mail dot ru
2021-02-05 17:58 ` [Bug libstdc++/98978] " redi at gcc dot gnu.org
2021-02-05 18:00 ` redi at gcc dot gnu.org
2021-02-05 20:44 ` andysem at mail dot ru
2021-02-06 17:26 ` redi at gcc dot gnu.org [this message]
2021-08-31 16:24 ` redi at gcc dot gnu.org
2022-09-07 12:30 ` redi at gcc dot gnu.org
2022-09-18 12:27 ` andysem at mail dot ru

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bug-98978-4-mLvt4x2V0u@http.gcc.gnu.org/bugzilla/ \
    --to=gcc-bugzilla@gcc.gnu.org \
    --cc=gcc-bugs@gcc.gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).