220 32457 <8361ebed-8ecb-44c6-9b36-6fbce460a952@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allow Structured Binding Outside of Variable Declaration Date: Mon, 15 May 2017 07:54:09 -0700 (PDT) Lines: 101 Approved: news@gmane.org Message-ID: <8361ebed-8ecb-44c6-9b36-6fbce460a952@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1452_1525024644.1494860049992" X-Trace: blaine.gmane.org 1494860050 25506 195.159.176.226 (15 May 2017 14:54:10 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 15 May 2017 14:54:10 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBEUC47EAKGQESMSTUAA@isocpp.org Mon May 15 16:54:06 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f198.google.com ([209.85.161.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dAHNu-0006XU-7c for gclcip-std-proposals@m.gmane.org; Mon, 15 May 2017 16:54:06 +0200 Original-Received: by mail-yw0-f198.google.com with SMTP id x186sf4538145ywg.10 for ; Mon, 15 May 2017 07:54:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=tFXowxjbU0m+eXYI3Pji6yQbU3qeW9bRH4UhX8L5mYQ=; b=UtvRJITwT1N+EMHh+AHfFtKUTK4nHDlOxom9wxoKkW/U03ncdO0pA3bqS9dDJIKKiQ W+bILUosO0Z42YTdWlS13h6N2x4fg9p8NXzdf6jo7cebrwpK7JH3sLY2s2e8gVcV2Hjv sFpDUv05WakXtpPX+UkU33rsOkqu9PAubAWxlmoVE0cluz5ZOYPU772WXRNy+8XcV6zP tMHO0VZq98kfdAWbEBQhZE4M20Akhlti0wQvnXdeQ6wygTJyZFklGr6TcxQGDKME4LrZ h+HnNfP9A5wM7oeHL9V7PqpzsSNnC6qvvk5/1ONYfB+Ey/JjenxVE+c4PPJ2Q8tI0jlo 86yA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=tFXowxjbU0m+eXYI3Pji6yQbU3qeW9bRH4UhX8L5mYQ=; b=qkTnLSAjNwN94BnTX7YDwIMTpvqnZKxPgkSrwvyogVKiw30Iyvh5CNmyUGmCi6zj+0 RzL9e6qLGcoy/A4r4PcqWY7hVxnaZJN7bJxmG+Z+Zm0SkxyhBfoNXA7yM++iyCXIKCN+ SAy5zzzKCMJUgqZwwBZdP4pscHRvgpYJj6larQuEjpyRaX7YuTlb7VhJ/sDZuY1V17Vj gw5mljyFYKplJpM2uEZcyAvvMu14Ok305na9jGDii0zyFYi5jwnKfuOLqZZeRUwN41hV mgNvMPalOKDpiobrI6glyYGg31satWGJHslFvPzRQ7XVDRE61qpYk6b1R/D1n4O3EXi/ 1x9g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=tFXowxjbU0m+eXYI3Pji6yQbU3qeW9bRH4UhX8L5mYQ=; b=JSStupPgpGRdj0RNMPa4qgKrVHqGtDUzOBz2a4vcfTviNpqWnyQN72a94XcKA7/qlj Ng//d9OxbzjrAVxZYiXE3MEa1g5fxRJgVtcIzIpZlHgqQ4GaOBb8FoTvVCUjfbrAseCc waN/OkWDx31v1vM0rQ/CWPI78dbZEaUGcK1TpZ1iJ1D9/ESOws+w79IkVIwrUCtyl8Yz KR5WaJ9MiXwq5V4XjTYamtzoLeGowwXehi0oZ8UkN2S44SPF765ppqbCbT14GNHDpYYy rudWk6CxF6V5GBbYgh8WixFdCd9F4jWd5SmKLALRuA+Tb4ep7LXqcg4A+J+m94eAkS1v 6eCw== X-Gm-Message-State: AODbwcAOW7/vA/ITMvcTH3kOfQyjQCpD6rOv6+2Tl58hQuPQItjGlBi8 +wa5ZeVyF5sQrA== X-Received: by 10.13.212.203 with SMTP id w194mr3180304ywd.38.1494860051528; Mon, 15 May 2017 07:54:11 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.60.102 with SMTP id j35ls13582508ote.13.gmail; Mon, 15 May 2017 07:54:10 -0700 (PDT) X-Received: by 10.157.40.242 with SMTP id s105mr133404ota.5.1494860050528; Mon, 15 May 2017 07:54:10 -0700 (PDT) In-Reply-To: X-Original-Sender: jmckesson@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:32457 Archived-At: ------=_Part_1452_1525024644.1494860049992 Content-Type: multipart/alternative; boundary="----=_Part_1453_1096682095.1494860049992" ------=_Part_1453_1096682095.1494860049992 Content-Type: text/plain; charset="UTF-8" On Monday, May 15, 2017 at 6:00:06 AM UTC-4, Antonio Perez wrote: > > Structured Binding is a language feature that has a lot of potential, > although as of C++17 it's a pretty limited feature. (This is part of a > series of proposals generalizing structured binding). I propose allowing > structured binding outside of variable declaration: > > int a = 0; > //Random code > std::string text =""; > //More code > [a,text] = tuple(3, "Hello, world"); > > You still need the `auto` there. You may not be creating the variables `a` and `text`, but you *are* creating a hidden variable to store the prvalue. So it's still a variable declaration. A more important question is this: exactly how does this work? Structured binding's behavior is a bit different for structs/arrays than it is for tuple-like types. If that were a struct, then `a` and `text` would not be reference variables to those members. They would actually *be those members*; the compiler would substitute the `a` and `text` identifiers for exactly those members. So how would that work if the variable already exists? -- 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/8361ebed-8ecb-44c6-9b36-6fbce460a952%40isocpp.org. ------=_Part_1453_1096682095.1494860049992 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Monday, May 15, 2017 at 6:00:06 AM UTC-4, Antonio Perez= wrote:
Struct= ured Binding is a language feature that has a lot of potential, although as= of C++17 it's a pretty limited feature. (This is part of a series of p= roposals generalizing structured binding). I propose allowing structured bi= nding outside of variable declaration:

int a =3D = 0;
//Random code
std::= string = text =3D"";
//More code
[a,text] =3D tuple(3, "Hello, world");


You still need the `auto` there. You may not be creating t= he variables `a` and `text`, but you are creating a hidden variable = to store the prvalue. So it's still a variable declaration.

A mo= re important question is this: exactly how does this work? Structured bindi= ng's behavior is a bit different for structs/arrays than it is for tupl= e-like types. If that were a struct, then `a` and `text` would not be refer= ence variables to those members. They would actually be those members; the compiler would substitute the `a` and `text` identifiers for exactly= those members.

So how would that work if the variable already exist= s?

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/8361ebed-8ecb-44c6-9b36-6fbce460a952= %40isocpp.org.
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