220 32504 article Path: news.gmane.org!.POSTED!not-for-mail From: Zhihao Yuan Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Allow Structured Binding Outside of Variable Declaration Date: Tue, 16 May 2017 17:43:58 -0500 Lines: 98 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> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="f403045c50565645bc054fabe857" X-Trace: blaine.gmane.org 1494974642 17171 195.159.176.226 (16 May 2017 22:44:02 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 16 May 2017 22:44:02 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBCSKRWMD4EHBBMMB53EAKGQEN566MPQ@isocpp.org Wed May 17 00:43:57 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f72.google.com ([209.85.214.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dAlC9-0004Jj-1H for gclcip-std-proposals@m.gmane.org; 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[184.173.153.196]) by mx.google.com with UTF8SMTPS id g2si170029qte.191.2017.05.16.15.44.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 May 2017 15:44:01 -0700 (PDT) Received-SPF: pass (google.com: domain of bounce+3f9131.69110-std-proposals=isocpp.org@miator.net designates 184.173.153.196 as permitted sender) client-ip=184.173.153.196; Original-Sender: zy@miator.net X-Mailgun-Sending-Ip: 184.173.153.196 X-Mailgun-Sid: WyI3MTBkYiIsICJzdGQtcHJvcG9zYWxzQGlzb2NwcC5vcmciLCAiNjkxMTAiXQ== Original-Received: from mail-pg0-f53.google.com (mail-pg0-f53.google.com [74.125.83.53]) by mxa.mailgun.org with ESMTP id 591b80b0.7fce98184270-smtp-out-n02; Tue, 16 May 2017 22:44:00 -0000 (UTC) Original-Received: by mail-pg0-f53.google.com with SMTP id u28so83045721pgn.1 for ; Tue, 16 May 2017 15:44:00 -0700 (PDT) X-Received: by 10.99.109.130 with SMTP id i124mr337970pgc.117.1494974639520; Tue, 16 May 2017 15:43:59 -0700 (PDT) Original-Received: by 10.100.151.71 with HTTP; Tue, 16 May 2017 15:43:58 -0700 (PDT) In-Reply-To: X-Gmail-Original-Message-ID: X-Original-Sender: zy@miator.net X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@miator.net; spf=pass (google.com: domain of bounce+3f9131.69110-std-proposals=isocpp.org@miator.net designates 184.173.153.196 as permitted sender) smtp.mailfrom=bounce+3f9131.69110-std-proposals=isocpp.org@miator.net 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:32504 Archived-At: --f403045c50565645bc054fabe857 Content-Type: text/plain; charset="UTF-8" On Tue, May 16, 2017 at 5:36 PM, Ville Voutilainen < ville.voutilainen@gmail.com> wrote: > > How about this > > > > for (TupleLike [x, y] : something) { ... } > > > > Where TupleLike is a concept. > > How does that help me specify the concrete types of the bindings? It does type-check, as same as you putting static_assert(is_same_v); in the loop. But it doesn't change the type object of the underlying object, or the type of the bindings. If you want to bind to different types, you can cast one the right hand side: auto [x, y] = rebind(something); where `rebind` converts a tuple-like to a std::tuple, or some thin wrappers if you prefer. -- Zhihao Yuan, ID lichray The best way to predict the future is to invent it. _______________________________________________ -- 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 email 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/CAGsORuDWRidpKi6nj5Bm8m%2BhHTy7PVKzzZFq_%3DvaA7XMdb3odw%40mail.gmail.com. --f403045c50565645bc054fabe857 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

= On Tue, May 16, 2017 at 5:36 PM, Ville Voutilainen <ville.voutil= ainen@gmail.com> wrote:
> How about this
>
>=C2=A0 =C2=A0for (TupleLike<A, B> [x, y] : something) { ... }
>
> Where TupleLike is a concept.

How does that help me specify the concrete types of the bindings?

It does type-check, as= same as you putting

=C2=A0 static_assert(i= s_same_v<decltype(x), A>);

in the loop.

But it doesn't change the = type object of the
underlying object, or the type of the bindings.

If you want to b= ind to different types, you can
= cast one the right hand side:

=
=C2=A0 auto [x, y] =3D = rebind<NewA, NewB>(something);

where `rebind` converts a tuple-like to a=
std::tuple, or some thin wrappers if you prefer.

--
Zhihao Yuan, ID lichr= ay
The best way to predict the future is to invent it.
______________= _________________________________

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