From: Matt Austern <austern@apple.com>
To: gcc mailing list <gcc@gcc.gnu.org>
Subject: generalized lvalues
Date: Thu, 18 Nov 2004 03:50:00 -0000 [thread overview]
Message-ID: <8AD5AEEF-3914-11D9-8BD2-000A95BCF344@apple.com> (raw)
Could somebody remind me, please, of the reasons we removed generalized
lvalues? I know there were several reasons, but I'm not sure if I've
ever seen a complete list. Here are the reasons I can reconstruct from
memory:
1. It broke valid C++ programs. If we overload a function on
constness, like foo(int&) and foo(const int&), then invoking it as
foo((int) x) is required to call the const version. Generalized
lvalues made us choose the latter.
2. It was underspecified. There were cases, again especially in C++ in
the presence of operator overloading, where nobody was quite sure
either what it did or what it was supposed to do.
3. I have the vague sense that it caused back end bugs, but I can't
find them offhand.
Anything else? (Incidentally, I think all of these apply to
cast-as-lvalue. I haven't heard of any problems caused by
conditional-as-lvalue or comma-expression-as-lvalue.)
The reason I'm asking: I think some people are going to find the
removal a nasty surprise. Yes, it was deprecated in 3.3.x and 3.4.x,
but not everyone upgrades to the latest release of older branches. I
imagine some people won't have noticed the discussion about removal
until they upgrade to 4.0 and see that it's gone. At that point we'll
have three choices: convince them that removing it made the compiler
better, or reconsider and put it back, or refuse to put it back, don't
tell anyone why it's gone, and live with unhappy users who think we're
stupid and capricious. If we want to go with one of the first two
options, it'll help to have a collection of reasons.
--Matt
next reply other threads:[~2004-11-18 3:47 UTC|newest]
Thread overview: 116+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-18 3:50 Matt Austern [this message]
2004-11-18 3:52 ` Andrew Pinski
2004-11-18 4:01 ` Andrew Pinski
2004-11-18 4:18 ` Daniel Berlin
2004-11-18 4:21 ` Andrew Pinski
2004-11-18 4:27 ` Matt Austern
2004-11-18 7:15 ` Joe Buck
2004-11-18 7:37 ` Matt Austern
2004-11-18 13:17 ` Giovanni Bajo
2004-11-18 17:57 ` Joe Buck
2004-11-18 18:28 ` Mike Stump
2004-11-18 18:44 ` Joe Buck
2004-11-19 1:39 ` Mike Stump
2004-11-19 4:52 ` Matt Austern
2004-11-19 22:24 ` Michael Matz
2004-11-19 22:30 ` Robert McNulty Junior
2004-11-20 1:00 ` Ziemowit Laski
2004-11-20 1:20 ` Joe Buck
2004-11-20 1:51 ` Ziemowit Laski
2004-11-20 5:04 ` Joe Buck
2004-11-20 5:17 ` Ziemowit Laski
2004-11-22 20:54 ` generalized lvalues -- patch outline Ziemowit Laski
2004-11-22 21:01 ` Andrew Pinski
2004-11-22 21:11 ` Ziemowit Laski
2004-11-22 21:39 ` Matt Austern
2004-11-22 22:11 ` Joe Buck
2004-11-22 22:12 ` Matt Austern
2004-11-23 0:06 ` Gabriel Dos Reis
2004-11-23 0:04 ` Gabriel Dos Reis
2004-11-23 0:27 ` Mike Stump
2004-11-24 20:40 ` Kai Henningsen
2004-11-23 0:11 ` Mark Mitchell
2004-11-23 1:19 ` Matt Austern
2004-11-23 1:26 ` Mark Mitchell
2004-11-23 1:32 ` Dale Johannesen
2004-11-23 1:42 ` Mark Mitchell
2004-11-23 1:45 ` Andrew Pinski
2004-11-23 1:55 ` Dale Johannesen
2004-11-23 1:56 ` Andrew Pinski
2004-11-23 2:12 ` Dale Johannesen
2004-11-23 2:10 ` Marcus G. Daniels
2004-11-23 9:43 ` Eric Botcazou
2004-11-23 18:27 ` Aaron W. LaFramboise
2004-11-22 21:23 ` Nathan Sidwell
2004-11-22 22:33 ` Ziemowit Laski
2004-11-23 0:09 ` Gabriel Dos Reis
2004-11-23 9:54 ` Nathan Sidwell
2004-11-23 13:35 ` Michael Matz
2004-11-23 14:56 ` Daniel Berlin
2004-11-23 15:02 ` Michael Matz
2004-11-23 15:15 ` Andrew Pinski
2004-11-23 15:47 ` Michael Matz
2004-11-23 15:56 ` Gabriel Dos Reis
2004-11-23 15:50 ` Steve Naroff
2004-11-23 15:51 ` Gabriel Dos Reis
2004-11-23 16:50 ` Eric Botcazou
2004-11-23 17:01 ` Paul Koning
2004-11-23 17:16 ` Andreas Schwab
2004-11-23 18:03 ` Thomas Kunert
2004-11-23 18:30 ` Nathan Sidwell
2004-11-23 18:57 ` Thomas Kunert
2004-11-23 21:21 ` Paul Koning
2004-11-23 21:52 ` Thomas Kunert
2004-11-23 15:51 ` Gabriel Dos Reis
2004-11-23 16:12 ` Michael Matz
2004-11-23 16:31 ` Richard Guenther
2004-11-23 16:44 ` Andreas Schwab
2004-11-23 20:16 ` Gabriel Dos Reis
2004-11-23 15:01 ` Nathan Sidwell
2004-11-23 15:09 ` Michael Matz
2004-11-23 19:11 ` Matt Austern
2004-11-23 21:10 ` Eric Botcazou
2004-11-23 21:34 ` Ziemowit Laski
2004-11-23 22:09 ` Joseph S. Myers
2004-11-23 22:23 ` Eric Botcazou
2004-11-23 22:27 ` Joseph S. Myers
2004-11-24 0:05 ` Eric Botcazou
2004-11-24 0:07 ` Steven Bosscher
2004-11-24 0:32 ` Joseph S. Myers
2004-11-25 8:41 ` Ian Lance Taylor
2004-11-25 20:41 ` Gabriel Dos Reis
2004-11-25 21:54 ` Matt Austern
2004-11-25 23:27 ` Gabriel Dos Reis
2004-11-29 18:06 ` Joe Buck
2004-11-29 18:57 ` Matt Austern
2004-11-23 23:27 ` Gabriel Dos Reis
2004-11-23 22:24 ` Nathan Sidwell
2004-11-23 0:07 ` Gabriel Dos Reis
2004-11-24 20:43 ` Kai Henningsen
2004-11-24 23:09 ` Gabriel Dos Reis
2004-11-24 23:17 ` Zack Weinberg
2004-11-22 21:31 ` Richard Henderson
2004-11-23 0:11 ` Gabriel Dos Reis
2004-11-23 0:03 ` Jonathan Lennox
2004-11-20 1:40 ` generalized lvalues Joseph S. Myers
2004-11-18 19:11 ` Alex Rosenberg
2004-11-18 4:24 ` Matt Austern
2004-11-18 5:33 ` Dale Johannesen
2004-11-18 17:14 ` Fariborz Jahanian
2004-11-18 18:23 ` Joe Buck
2004-11-19 0:20 ` Ziemowit Laski
2004-11-19 0:40 ` Steven Bosscher
2004-11-19 1:20 ` Joe Buck
2004-11-19 2:00 ` Ziemowit Laski
2004-11-18 23:36 ` Ziemowit Laski
2004-11-18 23:37 ` Matt Austern
2004-11-18 23:49 ` Zack Weinberg
2004-11-19 1:38 ` Ziemowit Laski
2004-11-19 2:52 ` Zack Weinberg
2004-11-19 3:56 ` Ziemowit Laski
2004-11-19 4:22 ` Zack Weinberg
2004-11-19 13:10 ` Nathan Sidwell
2004-11-19 21:58 ` Ziemowit Laski
2004-11-18 23:44 ` Andrew Pinski
2004-11-18 23:45 ` Joe Buck
2004-11-25 4:42 ` Aaron W. LaFramboise
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=8AD5AEEF-3914-11D9-8BD2-000A95BCF344@apple.com \
--to=austern@apple.com \
--cc=gcc@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).