220 39261 article Path: news.gmane.org!.POSTED!not-for-mail From: Arthur O'Dwyer Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Move destructor draft Date: Fri, 20 Jul 2018 16:23:44 -0700 (PDT) Lines: 157 Approved: news@gmane.org Message-ID: References: <0A99E209-333B-4140-8F65-2F022E681AC1@gmail.com> <55C0DDD4.8090100@halpernwightsoftware.com> <411A67D7-B062-4D22-983A-095737483208@gmail.com> <55C299B0.1060300@gmail.com> <55C2ABA3.8060605@halpernwightsoftware.com> <55C2ECDB.1060307@gmail.com> <5de71605-7320-4130-938b-813304c51069@isocpp.org> < mq2f45$k25$1@ger.gmane.org> <94331665-f7f3-444 b-a1dc-333a52be7873@isocpp.org> <80721d48-888b-4dc8-b938-28f2ca329f04@isocpp.org> <258bb255-f100-4667-bd25-af470b6d5d5f@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_6755_581585786.1532129024372" X-Trace: blaine.gmane.org 1532128901 28265 195.159.176.226 (20 Jul 2018 23:21:41 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 20 Jul 2018 23:21:41 +0000 (UTC) Cc: mihailnajdenov@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDLZJYWNDQIIDXWJ3ICRUBDXZO3OE@isocpp.org Sat Jul 21 01:21:36 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f197.google.com ([209.85.213.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fgeiN-0007FT-RX for gclcip-std-proposals@m.gmane.org; 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Fri, 20 Jul 2018 16:23:46 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a0d:cb82:: with SMTP id n124-v6ls391804ywd.14.gmail; Fri, 20 Jul 2018 16:23:45 -0700 (PDT) X-Received: by 2002:a0d:de01:: with SMTP id h1-v6mr118654ywe.3.1532129025270; Fri, 20 Jul 2018 16:23:45 -0700 (PDT) In-Reply-To: <258bb255-f100-4667-bd25-af470b6d5d5f@isocpp.org> X-Original-Sender: arthur.j.odwyer@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:39261 Archived-At: ------=_Part_6755_581585786.1532129024372 Content-Type: multipart/alternative; boundary="----=_Part_6756_1699092616.1532129024372" ------=_Part_6756_1699092616.1532129024372 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Friday, July 20, 2018 at 9:55:38 AM UTC-7, mihailn...@gmail.com wrote: > > > Does anyone know what happened to this proposal and destructive move in= =20 > general? It seems the current [[trivially relocatable]] covers similar=20 > ground, but it is not the same - it can't, well, move-destruct (AFAICC). > > Is destructive move dead now, in favor of just marking the types, already= =20 > "trivially relocatable"?=20 > My impression is that previous proposals to introduce a new first-class=20 spelling (such as Denis's >>T(T&)) have not made much headway against the= =20 Committee. Therefore, both my upcoming P1144=20 =20 "Object relocation in terms of move plus destroy" and Niall's P1029=20 "[[move_relocates]]" try to express the idea in terms of composing existing= =20 operations: - P1144 says "always (relocate =3D move + destroy), and sometimes (relocate= =3D=20 memcpy + drop)" - P1029 says "sometimes (move =3D memcpy + drop + default-construct)" I'd be interested to talk more about "[P1144] can't, well, move-destruct" = =E2=80=94=20 perhaps in a new dedicated thread, though. I'd also like to hear from anyone who was involved in actual discussions of= =20 N4158, P0023, etc. I have just now found the LEWG discussion of Pablo's N4034 (June 2014,=20 Rapperswil): - http://wiki.edg.com/bin/view/Wg21rapperswil2014/N4034 And the EWG discussion of Pablo's N4158 (November 2014, Urbana): - http://wiki.edg.com/bin/view/Wg21urbana-champaign/EvolutionWorkingGroup#N= 4158_Destructive_Move_Rev_1 It looks like things were generally favorable: LEWG sent it quickly to LWG,= =20 LWG bounced it back to EWG due to the unexploredness of std::bless/launder= =20 at the time, EWG expressed concern with the lack of std::bless/launder but= =20 "encouraged more work in this direction" (of course); and then it fell into= =20 a black hole and never emerged again. My hope, as you can tell, is that now that we have explored ways of=20 blessing "regions of storage" so that they become "objects" (so that=20 std::vector is almost implementable these days! ;)) that some of EWG's=20 concerns may have been alleviated. Also, N4158 lacked a public=20 implementation that provably worked with things like allocators, whereas=20 P1144 thinks the proper interaction with allocators is so easy=20 the paper doesn't even talk about them. =E2=80=93Arthur --=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/fb8001ef-9dbc-4016-a60f-a4dfa55f275c%40isocpp.or= g. ------=_Part_6756_1699092616.1532129024372 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Friday, July 20, 2018 at 9:55:38 AM UTC-7, mihailn...@g= mail.com wrote:

Does anyone know what happened to this proposal and d= estructive move in general? It seems the current [[trivially relocatable]] = covers similar ground, but it is not the same - it can't, well, move-de= struct (AFAICC).

Is destructive move dead now, in favor of ju= st marking the types, already "trivially relocatable"?=C2=A0

My impression is that previous p= roposals to introduce a new first-class spelling (such as Denis's >>T(T&)) have not made mu= ch headway against the Committee. Therefore, both my upcoming P1144 "Object relocation in terms of move plus destroy" a= nd Niall's P1029 "[[move_relocates]]" try to express the idea= in terms of composing existing operations:
- P1144 says "al= ways (relocate =3D move + destroy), and sometimes (relocate =3D memcpy + dr= op)"
- P1029 says "sometimes (move =3D memcpy + drop + = default-construct)"

I'd be interested to = talk more about "[P1144] can't, well, move-destruct" =E2=80= =94 perhaps in a new dedicated thread, though.

I&#= 39;d also like to hear from anyone who was involved in actual discussions o= f N4158, P0023, etc.

I have just now found the LEW= G discussion of Pablo's N4034 (June 2014, Rapperswil):
-=C2= =A0http://wiki.edg.com/bin/view/Wg21rapperswil2014/N4034
And the = EWG discussion of Pablo's N4158 (November 2014, Urbana):
-=C2= =A0http://wiki.edg.com/bin/view/Wg21urbana-champaign/EvolutionWorkingGroup#= N4158_Destructive_Move_Rev_1

It looks like things = were generally favorable: LEWG sent it quickly to LWG, LWG bounced it back = to EWG due to the unexploredness of std::bless/launder at the time, EWG exp= ressed concern with the lack of std::bless/launder but "encouraged mor= e work in this direction" (of course); and then it fell into a black h= ole and never emerged again.

My hope, as you can t= ell, is that now that we have explored ways of blessing "regions of st= orage" so that they become "objects" (so that std::vector is= almost implementable these days! ;)) that some of EWG's concerns may h= ave been alleviated. =C2=A0Also, N4158 lacked a public implementation that = provably worked with things like allocators, whereas P1144 thinks the prope= r interaction with allocators is=C2=A0so easy the paper doesn't even talk about them.

<= /div>
=E2=80=93Arthur

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