220 19940 <920F56A3-A113-45D4-9CFF-98B941F013C5@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: default arguments Date: Thu, 20 Aug 2015 15:10:54 +0800 Lines: 137 Approved: news@gmane.org Message-ID: <920F56A3-A113-45D4-9CFF-98B941F013C5@gmail.com> References: <89bf9d09-00ed-45db-bf88-39c844707bd1@isocpp.org> <5F6E90B3-44BE-4A37-BE8F-91E1255E6407@gmail.com> <124ba022-8377-4ba3-be25-23e2134a9549@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_5C8BF3B8-BE47-48D0-B5F8-273C6BB21D04" X-Trace: ger.gmane.org 1440054671 18888 80.91.229.3 (20 Aug 2015 07:11:11 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 20 Aug 2015 07:11:11 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCW25A7E3QCRBBP32WXAKGQEREDOJXI@isocpp.org Thu Aug 20 09:11:04 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f200.google.com ([209.85.220.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZSK07-0007wE-Be for gclcip-std-proposals@m.gmane.org; Thu, 20 Aug 2015 09:11:03 +0200 Original-Received: by qkep139 with SMTP id p139sf36855340qke.1 for ; Thu, 20 Aug 2015 00:11:02 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:content-type:message-id:mime-version :subject:date:references:to:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=0uf2iUO3XG3xlutkheMlTu+TkHrS2/Y/lUS1EbTvcY8=; b=jWNKix8cuxFyFo0F0Hvj8xmqKRGiW/gMQsw4vRGIwdVvA+dsJ6BoHKj7DP9eL7vtbj tzgYcu6hAqdsW+8FlydDkFoK0i/GDzmquYlpHKLHzEuGoFJFLXI6jDTT2kT1AFYnmbxD OjaMTE3sKkIarfdOkPEVZZE0BEy5Lj1GEtV+N5dg3tqQACI6stxRlgXyPjIRlmi7tZBq Hm+jfbmtdv7qL2uK1sD2kDzNkDbpYmlxvYFhEDHvFFqr1g9I5EVqbV9F0ymMkNH0sMwR 7bmTxQomN03D0T9HdlaWzsux1qf0EaaPbGwG42oYJ6+/vtNzWTvg72CQT7ABRb31qDus 0JxQ== X-Gm-Message-State: ALoCoQkszioE2iO30OlGyJiyKX1tP7EmrePm5PmC35i7i20T1gq8qOPamCXSw9UoJQsiLMiZ4h48 X-Received: by 10.52.226.202 with SMTP id ru10mr1202861vdc.4.1440054662317; Thu, 20 Aug 2015 00:11:02 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.34.79 with SMTP id i76ls363801ioi.25.gmail; Thu, 20 Aug 2015 00:11:01 -0700 (PDT) X-Received: by 10.70.135.198 with SMTP id pu6mr3589766pdb.159.1440054661239; Thu, 20 Aug 2015 00:11:01 -0700 (PDT) Original-Received: from mail-pd0-x232.google.com (mail-pd0-x232.google.com. [2607:f8b0:400e:c02::232]) by mx.google.com with ESMTPS id qn16si5982513pab.174.2015.08.20.00.11.01 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 20 Aug 2015 00:11:01 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::232 as permitted sender) client-ip=2607:f8b0:400e:c02::232; Original-Received: by pdbfa8 with SMTP id fa8so10965197pdb.1 for ; Thu, 20 Aug 2015 00:11:01 -0700 (PDT) X-Received: by 10.70.20.196 with SMTP id p4mr3674499pde.58.1440054660905; Thu, 20 Aug 2015 00:11:00 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.176]) by smtp.gmail.com with ESMTPSA id au10sm3108931pbd.81.2015.08.20.00.10.58 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 20 Aug 2015 00:11:00 -0700 (PDT) In-Reply-To: <124ba022-8377-4ba3-be25-23e2134a9549@isocpp.org> X-Mailer: Apple Mail (2.2098) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::232 as permitted sender) smtp.mailfrom=potswa@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-Spam-Checked-In-Group: std-proposals@isocpp.org 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:19940 Archived-At: --Apple-Mail=_5C8BF3B8-BE47-48D0-B5F8-273C6BB21D04 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 > On 2015=E2=80=9308=E2=80=9320, at 11:59 AM, Nicol Bolas wrote: >=20 > What you're doing is enforcing a single struct policy, which is not somet= hing I would want to see advocated or become commonplace. However, it does = lack the terrible syntactic noise of the C version, so it's already ahead o= f the curve ;) One is better than zero=E2=80=A6 but what=E2=80=99s the impediment to group= ing by nested sub-aggregates? > The problem with that is that NSDMI's operate by effectively modifying co= nstructors. Since C++14, NSDMIs have a second method of action, by aggregate initializa= tion. They are already allowed in aggregates. > As for the implicit braces thing, that sounds like a very bad idea. Unifo= rm initialization already has way too many implicit braces, to the point wh= ere it actually gets non-uniform. It's two extra characters; I don't see it= as provoking that much syntactic noise. Hmm, are you for the proposal or against? Implicit braces are the entirety = of it. (Note that Clang and GCC already implement designated initializers, = both only issuing a warning under -pedantic.) And they specifically don=E2= =80=99t apply under brace (uniform) initialization. The problem with adding designated initializers alone is that they enhance = aggregates but not classes with constructors. This impedes refactoring an a= ggregate into a non-aggregate, which is a very common operation. If you look closer, there is a common syntax (already compatible with GCC <= http://coliru.stacked-crooked.com/a/b5ecf9099e190e01> and Clang for initializing an aggregate w= ith designated initializers or a non-aggregate by a =E2=80=9Cvalue prototyp= e=E2=80=9D aggregate, which is to use both parens and braces as foo({.x =3D= 42}). It=E2=80=99s not that much typing, but it=E2=80=99s too much to be i= diomatic, especially for a quick-and-dirty aggregate that just might become= more complex later. So, my suggestion is to use parens with designated initializers as a common= ground between aggregates and constructors. If you=E2=80=99re writing an a= ggregate that perhaps shouldn=E2=80=99t be an aggregate, it encourages you = to use parens and designated initializers. This should have the added benef= it of reducing abuse of =E2=80=9Cuniform=E2=80=9D initialization to call or= dinary constructors. On the other hand, most such aggregates only have 2-3 = members, and splitting out the parameter class is a bit of extra effort and= noise. --=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/. --Apple-Mail=_5C8BF3B8-BE47-48D0-B5F8-273C6BB21D04 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=UTF-8
On 2= 015=E2=80=9308=E2=80=9320, at 11:59 AM, Nicol Bolas <jmckesson@gmail.com> wrote:

What you're doing is enforcing a= single struct policy, which is not something I would want to see advocated= or become commonplace. However, it does lack the terrible syntactic noise = of the C version, so it's already ahead of the curve ;)

One is better than zero= =E2=80=A6 but what=E2=80=99s the impediment to grouping by nested sub-aggre= gates?

The problem with that is that NSDMI's operate by effe= ctively modifying constructors.

Since C++14, NSDMIs have a second method of action, by aggrega= te initialization. They are already allowed in aggregates.

= As for the implicit braces thing, that sounds like a very bad idea. Uniform= initialization already has way too many implicit braces, to the point wher= e it actually gets non-uniform. It's two extra characters; I don't see it a= s provoking that much syntactic noise.

Hmm, are you for the proposal or against= ? Implicit braces are the entirety of it. (Note that Clang and GCC already = implement designated initializers, both only issuing a warning under -pedan= tic.) And they specifically don=E2=80=99t apply under brace (uniform) initi= alization.

The pr= oblem with adding designated initializers alone is that they enhance aggreg= ates but not classes with constructors. This impedes refactoring an aggrega= te into a non-aggregate, which is a very common operation.

If you look closer, there is a c= ommon syntax (already compatible with GCC and Clang<= /a> for initializing an aggregate with designated initializers or a no= n-aggregate by a =E2=80=9Cvalue prototype=E2=80=9D aggregate, which is to u= se both parens and braces as foo({.x =3D = 42}). It=E2=80=99s not that much typing, but = it=E2=80=99s too much to be idiomatic, especially for a quick-and-dirty agg= regate that just might become more complex later.

So, my suggestion is to use parens with de= signated initializers as a common ground between aggregates and constructor= s. If you=E2=80=99re writing an aggregate that perhaps shouldn=E2=80=99t be= an aggregate, it encourages you to use parens and designated initializers.= This should have the added benefit of reducing abuse of =E2=80=9Cuniform= =E2=80=9D initialization to call ordinary constructors. On the other hand, = most such aggregates only have 2-3 members, and splitting out the parameter= class is a bit of extra effort and noise.

--

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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
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