220 32503 article Path: news.gmane.org!.POSTED!not-for-mail From: "Arthur O'Dwyer" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Allow Structured Binding Outside of Variable Declaration Date: Tue, 16 May 2017 15:41:01 -0700 Lines: 114 Approved: news@gmane.org Message-ID: References: <10b21241-b683-44d5-82ce-90681b2643a4@isocpp.org> <08ff73f1-6989-393e-ee4e-8158af2e7bed@honermann.net> <20170516164245.GA16348@fukushima.lysator.liu.se> <586c2633-4586-12d8-35ae-75ebab176ff8@honermann.net> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="94eb2c195864c25c1d054fabdd64" X-Trace: blaine.gmane.org 1494974465 462 195.159.176.226 (16 May 2017 22:41:05 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 16 May 2017 22:41:05 +0000 (UTC) To: "ISO C++ Standard - Future Proposals" Original-X-From: std-proposals+bncBDLZJYWNDQIP577NZACRUBBJCYCRE@isocpp.org Wed May 17 00:40:58 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f70.google.com ([209.85.215.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dAl9G-0008M8-4P for gclcip-std-proposals@m.gmane.org; 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[2a00:1450:400c:c09::22a]) by mx.google.com with ESMTPS id v62si15298292wmb.41.2017.05.16.15.41.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 May 2017 15:41:02 -0700 (PDT) Received-SPF: pass (google.com: domain of arthur.j.odwyer@gmail.com designates 2a00:1450:400c:c09::22a as permitted sender) client-ip=2a00:1450:400c:c09::22a; Original-Received: by mail-wm0-x22a.google.com with SMTP id b84so147463360wmh.0 for ; Tue, 16 May 2017 15:41:02 -0700 (PDT) X-Received: by 10.80.152.194 with SMTP id j60mr598519edb.98.1494974462055; Tue, 16 May 2017 15:41:02 -0700 (PDT) Original-Received: by 10.80.154.33 with HTTP; Tue, 16 May 2017 15:41:01 -0700 (PDT) In-Reply-To: <586c2633-4586-12d8-35ae-75ebab176ff8@honermann.net> X-Original-Sender: arthur.j.odwyer@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of arthur.j.odwyer@gmail.com designates 2a00:1450:400c:c09::22a as permitted sender) smtp.mailfrom=arthur.j.odwyer@gmail.com; dmarc=pass (p=NONE sp=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:32503 Archived-At: --94eb2c195864c25c1d054fabdd64 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, May 16, 2017 at 2:53 PM, Tom Honermann wrote: > On 05/16/2017 05:12 PM, Bengt Gustafsson wrote: > > Why not let a variable declaration inside a structured binding be a > variable declaration? > > I eluded to this being a sound design in an earlier reply. Is there good > motivation for being able to declare a variable rather than a binding? I > find the current design highly motivating specifically because a binding = is > effectively an alias. > Speaking of "being able to declare a variable instead of a binding", this morning I ran across this example due to Tony van Eerd: struct Foo { int x =3D 0; std::string str =3D "world"; ~Foo() { std::cout << str; } }; int main() { auto [i, s] =3D Foo(); std::cout << "hello "; s =3D "structured bindings"; // Foo's destructor prints "hello structured bindings"! } ....which is the nail in the coffin of "ever using C++17 structured bindings in production code" AFAIC. =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/CADvuK0JFhG1anzEmHLg5%2BmhiLcHGU%2B31PRY%3DgWPhS= uG0Ejd5zw%40mail.gmail.com. --94eb2c195864c25c1d054fabdd64 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Tue, May 16, 2017 at 2:53 PM, Tom Honermann <tom@hon= ermann.net> wrote:
=20 =20 =20
On 05/16/201= 7 05:12 PM, Bengt Gustafsson wrote:
Why not let a variable declaration inside a structured binding be a variable declaration?
 I eluded to this being a sound design in an earlier reply.=C2=A0 Is the= re good motivation for being able to declare a variable rather than a binding?=C2=A0 I find the current design highly motivating specifically because a binding is effectively an alias.

<= /div>
Speaking of "being able to declare a variable instead of a b= inding", this morning I ran across this example due to Tony van Eerd:<= /div>

struct Fo= o {
=C2=A0 =C2=A0 int = x =3D 0;
=C2=A0 =C2=A0= std::string str =3D "world";
=C2=A0 =C2=A0 ~Foo() { std::cout << str; }
};

int main() {
= =C2=A0 =C2=A0 auto [i, s] =3D Foo();
=C2=A0 =C2=A0 std::cout << "hello ";<= /div>
=C2=A0 =C2=A0 s =3D "str= uctured bindings";
}

...which is the nail in the coffin of "ev= er using C++17 structured bindings in production code" AFAIC.

=E2=80=93Arthur

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