220 18364 article Path: news.gmane.org!not-for-mail From: "Arthur O'Dwyer" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Core Language feature: Multiple assignments from multiple return values via tuple Date: Tue, 2 Jun 2015 23:31:29 -0700 Lines: 160 Approved: news@gmane.org Message-ID: References: <69a59613-6504-466a-9878-786653d6087f@isocpp.org> <6F892DDD-D1C2-446F-84E6-A2B81D096B2B@gmail.com> <9f3a42b5-befc-42e9-b739-654675eb4e02@isocpp.org> <1603866.meDQjFxuP6@tjmaciei-mobl4> <20ff0095-a634-40a7-8c01-3b302ece9bd3@isocpp.org> <556E77F4.5010004@wanadoo.fr> <3e68596f-1a33-481c-acfe-c230b212234c@isocpp.org> <556E9CB0.6090403@wanadoo.fr> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=f46d0438940d8f64e1051797353f X-Trace: ger.gmane.org 1433313110 23902 80.91.229.3 (3 Jun 2015 06:31:50 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 3 Jun 2015 06:31:50 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDLZJYWNDQIMFPV2VMCRUBHXEHINU@isocpp.org Wed Jun 03 08:31:43 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wg0-f72.google.com ([74.125.82.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Z02D5-0007JE-DL for gclcip-std-proposals@m.gmane.org; Wed, 03 Jun 2015 08:31:31 +0200 Original-Received: by wgme6 with SMTP id e6sf98212wgm.3 for ; Tue, 02 Jun 2015 23:31:30 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=bo1gWUB6OpVloWANo7ep60o7SHWBautjpIqdko2YxaM=; b=UtouJwOOiJh+0AS3EUhKUEW437ZZotAIXsuNC1yBhncjUZ3+K24Ej58FC9vbPYlyPL 9PLDBgtpcEQQC6m6L36c5K0Kmsjbybqdhb902fB89H95YLl/cIoab/rheKvdBjKTXYzM mX0WdJqxa93f3psjPWlM35dZ5tIabv/fkfAU8zKaCE+ZsdE65wi3ss150iabzaZ5LpqE x1L1ahMYzQesrucqetpBtgmiLgrO84z21TGtyAxGfa1lr+Ua9SnawKgNqaszdzNGzEYX FFTx2MeoREPKJSIYAWuiI/cql4n+YdDE+NFzQt015EvOFPyciWRbCFfh9idjZpr6u6DY Hcdg== X-Gm-Message-State: ALoCoQnPp0wth8PhTRltm6SLl8MtPhyjNzSg2c6zesRMBLVhlSaEnOlgvrjYD8Jql7urdtV7NKQm X-Received: by 10.112.171.41 with SMTP id ar9mr29409593lbc.24.1433313090705; Tue, 02 Jun 2015 23:31:30 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.181.23.195 with SMTP id ic3ls1077547wid.49.canary; Tue, 02 Jun 2015 23:31:29 -0700 (PDT) X-Received: by 10.181.11.193 with SMTP id ek1mr38316686wid.15.1433313089743; Tue, 02 Jun 2015 23:31:29 -0700 (PDT) Original-Received: from mail-wi0-x22a.google.com (mail-wi0-x22a.google.com. [2a00:1450:400c:c05::22a]) by mx.google.com with ESMTPS id gd5si34958472wjb.115.2015.06.02.23.31.29 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Jun 2015 23:31:29 -0700 (PDT) Received-SPF: pass (google.com: domain of arthur.j.odwyer@gmail.com designates 2a00:1450:400c:c05::22a as permitted sender) client-ip=2a00:1450:400c:c05::22a; Original-Received: by wifw1 with SMTP id w1so9130134wif.0 for ; Tue, 02 Jun 2015 23:31:29 -0700 (PDT) X-Received: by 10.181.13.172 with SMTP id ez12mr1212662wid.91.1433313089642; Tue, 02 Jun 2015 23:31:29 -0700 (PDT) Original-Received: by 10.27.6.3 with HTTP; Tue, 2 Jun 2015 23:31:29 -0700 (PDT) In-Reply-To: <556E9CB0.6090403@wanadoo.fr> X-Original-Sender: arthur.j.odwyer@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of arthur.j.odwyer@gmail.com designates 2a00:1450:400c:c05::22a as permitted sender) smtp.mail=arthur.j.odwyer@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: 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:18364 Archived-At: --f46d0438940d8f64e1051797353f Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Tue, Jun 2, 2015 at 11:20 PM, Vicente J. Botet Escriba < vicente.botet@wanadoo.fr> wrote: > Le 03/06/15 06:50, Nicol Bolas a =C3=A9crit : > > On Tuesday, June 2, 2015 at 11:43:50 PM UTC-4, Vicente J. Botet Escriba > wrote: >> >> Le 03/06/15 00:39, Nicol Bolas a =C3=A9crit : >> >> On Tuesday, June 2, 2015 at 4:27:55 PM UTC-4, Thiago Macieira wrote: >>> >>> On Tuesday 02 June 2015 11:46:48 Nicol Bolas wrote: >>> > Except that there's plenty of elision of potential for user-defined >>> types. >>> > Indeed, modern C++ syntax is designed around the assumption that >>> elision >>> > exists and will make code as fast as possible. Every time you see >>> someone >>> > write `T t =3D stuff();` instead of an explicit `stuff(&t, );`, you a= re >>> > implicitly relying on elision to make this fast. >>> > >>> > Why should MRVs undo this syntactic progress? >>> >>> In fact, our investigation showed that compilers optimise inline >>> functions >>> with multiple return values (structs, pairs, tuples) better than those >>> with >>> output parameters. >>> >>> For an example, see https://codereview.qt-project.org/106089. >>> >> >> Glad to see that some compilers perform better with a functional >> interface, at least when functions are inlined. >> > In this decade, the idea that compilers are really good at value semantics (e.g. creating new values and returning them) and relatively not-so-good at reference semantics (e.g. passing around references to use as out-parameters) should not be shocking to anybody. *Of course* value semantics are going to win that fight. For those who need convincing, Chandler Carruth's keynote from CppCon 2013 covers this topic extremely well. https://www.youtube.com/watch?v=3DeR34r7HOU14 =E2=80=93Arthur --=20 ---=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. --f46d0438940d8f64e1051797353f Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Tue, Jun 2, 2015 at 11:20 PM, Vicente J. Botet Escriba = <vicente.botet@wanadoo.fr> wrote:
=20 =20 =20
Le 03/06/15 06:50, Nicol Bolas a =C3=A9crit=C2=A0:
On Tuesday, June 2, 2015 at 11:43:50 PM UTC-4, Vicente J. Botet Escriba wrote:
Le 03/06/15 00:39, Nicol Bolas a =C3=A9crit=C2=A0:
On Tuesday, June 2, 2015 at 4:27:55 PM UTC-4, Thiago Macieira wrote:
On Tuesday 02 June 2015 11:46:48 Nicol Bolas wrote:
> Except that there's plenty of elision of potential for user-defined types.
> Indeed, modern C++ syntax is designed around the assumption that elision
> exists and will make code as fast as possible. Every time you see someone
> write `T t =3D stuff();` instead of an explicit `stuff(&t, );`, you are
> implicitly relying on elision to make this fast.
>
> Why should MRVs undo this syntactic progress?

In fact, our investigation showed that compilers optimise inline functions
with multiple return values (structs, pairs, tuples) better than those with
output parameters.

For an example, see https://codereview.qt-pr= oject.org/106089.

Glad to see that some compilers perform better with a functional interface, at least when functions are inlined.

In this decade, the= idea that compilers are really good at value semantics (e.g. creating new = values and returning them) and relatively not-so-good at reference semantic= s (e.g. passing around references to use as out-parameters) should not be s= hocking to anybody. =C2=A0Of course value semantics are going to win= that fight.

For those who need convincing, Chandl= er Carruth's keynote from CppCon 2013 covers this topic extremely well.=
https://www.youtube.com/watch?v=3DeR34r7HOU14
=

=E2=80=93Arthur

--

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