220 32492 article Path: news.gmane.org!.POSTED!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Allow Structured Binding Outside of Variable Declaration Date: Tue, 16 May 2017 20:35:52 +0300 Lines: 36 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: text/plain; charset="UTF-8" X-Trace: blaine.gmane.org 1494956153 4917 195.159.176.226 (16 May 2017 17:35:53 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 16 May 2017 17:35:53 +0000 (UTC) To: "ISO C++ Standard - Future Proposals" Original-X-From: std-proposals+bncBC5JHI7A7ALRB6PQ5TEAKGQE7C6WSSY@isocpp.org Tue May 16 19:35:48 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f200.google.com ([209.85.213.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dAgNw-000196-FF for gclcip-std-proposals@m.gmane.org; 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[2607:f8b0:4003:c06::234]) by mx.google.com with ESMTPS id f124si1187684oig.186.2017.05.16.10.35.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 May 2017 10:35:53 -0700 (PDT) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:4003:c06::234 as permitted sender) client-ip=2607:f8b0:4003:c06::234; Original-Received: by mail-oi0-x234.google.com with SMTP id l18so34590634oig.2 for ; Tue, 16 May 2017 10:35:53 -0700 (PDT) X-Received: by 10.202.226.85 with SMTP id z82mr2242457oig.183.1494956152606; Tue, 16 May 2017 10:35:52 -0700 (PDT) Original-Received: by 10.157.17.253 with HTTP; Tue, 16 May 2017 10:35:52 -0700 (PDT) In-Reply-To: X-Original-Sender: ville.voutilainen@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:4003:c06::234 as permitted sender) smtp.mailfrom=ville.voutilainen@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:32492 Archived-At: On 16 May 2017 at 20:01, Tom Honermann wrote: >> What is wrong with the good old way? >> >> auto [SomeType x, =k->Key] = parseKey(); > > > There is the question of what happens if the decomposed type of the matching > element is not reference compatible with type 'SomeType'. Ill-formed? Does > 'x' change from being a structured binding to a variable of the declared > type? If so, are conversions performed? What type is decltype(x) and does Why on earth would it change from being a structured binding to something else? > it depend on the type of the matching element? A syntax that indicates a > type constraint (which is, I think, what is desired regardless of the syntax > used) rather than a variable declaration avoids these questions. Funny, such "type constraints" were something I always considered to be an integral and fundamental part of variable declarations. I don't write auto x = foo(); static_assert(is_same_v); but for some reason it's been suggested that I should do that for structured bindings, conveniently forgetting that then I will need to put that "type constraint" far far away from my structured bindings, like into a for-loop body when the structured binding is in the loop header. -- 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/CAFk2RUY1AYOen-Rb8n6yzc1jsOiydbUCUDqLdKMPyiyiHnnO4w%40mail.gmail.com. .