220 33349 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: P0329R0 falls short for designated initialisers Date: Wed, 26 Jul 2017 10:49:20 -0700 (PDT) Lines: 128 Approved: news@gmane.org Message-ID: References: <4892340.tBhI7hZKOg@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_3512_1575275533.1501091360807" X-Trace: blaine.gmane.org 1501091369 2342 195.159.176.226 (26 Jul 2017 17:49:29 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 26 Jul 2017 17:49:29 +0000 (UTC) Cc: d25fe0be@outlook.com, thiago@macieira.org, zy@miator.net To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBINM4PFQKGQEJK5RHTA@isocpp.org Wed Jul 26 19:49:24 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f197.google.com ([209.85.192.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1daQQv-0008Rp-Ao for gclcip-std-proposals@m.gmane.org; Wed, 26 Jul 2017 19:49:17 +0200 Original-Received: by mail-pf0-f197.google.com with SMTP id 72sf112757737pfl.12 for ; Wed, 26 Jul 2017 10:49:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=iLQbJGgMl0wrkE3xoYtBbbfJWsxpUysTs2KV0ClQQJ0=; b=k0ZOdIg0ovBozBjrIWnV43woCCvts80m1SFe9Lio1iHH4g10BG5CEVRulnCCP/Sk2i zPA9/5UMcWGhvWcaWGU8hKF1gSMttvuFM59trc4HctAWwGbQxB5wO5iq8gV5Wrxr3fsq kiP3wwZB0ZwrYst+YJAp7IPOs0gCora4Pci4Qq6kgq7LMvqwTO88hUiv5qBfbT2R9oDJ n/Vz2TEFo3sj+aHyeso+48ADO3yCOpgJ0O4/WqxMW0dGlR5q0B6k74oVbBZeYK62yFxB 1yEdVXFcUvdX4jdZpJsA1XCtBmUdKtXEsMIF9k9NVAzbuyoCb+RdoiJIoM8gODN7cU31 2oSg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=iLQbJGgMl0wrkE3xoYtBbbfJWsxpUysTs2KV0ClQQJ0=; b=kFHebyS5s2B8z1+QfnKfyGPtD4FDiDaDcVY6HDEV6Z3m67joqeMgTdoBU156d3fJXX GoaijttvSYZJ4DsFuFJf8mQ/VpjqU5D5CeXGTvT8M3tEuQ/tYutybpotFJ4LBZWJhnwq fRFzRRKJ7MqZ6WJcEIracT4t0zSEOg+g6ww8KKCR7C88jcl8wYsdPIXvI26PpivXGEV0 oeiATmvU8B2kXR2iuRfWt+a9vpzrbMJpBGRkSFieSL+gV21Wo6K8i6S8xQnOI9aLJGYg LtlQPtyb0CITqVJ7hR1ND00KqgEBHktw3IJHdQiYy5McVJt5hZxO/BdDx+5VqYZ+6+fV 3bYA== 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:cc: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=iLQbJGgMl0wrkE3xoYtBbbfJWsxpUysTs2KV0ClQQJ0=; b=gzH2muw2N/yeJJcI6dPIyXJBXpqf0tzcRNF+Bvsqazg9NuFKU1hxUdnF/DQqDEIuwi NaGZ7VR+9CTtGy0ySGlYTeqgDT+GGcJc6bEBteZLudg6ASt4W3qSO+rtWUyDWgsrzunv nhmv1sgkWp3xVQEDLJ0nUhKEp7BZ/fhBOlS4HkvILHLc+dgqa4b+PFjR0PjbI/4nFRPa DLE2I/eVJHh+jl6/74q7G/JliAhINmSH6Nxr/XHfpUuA3DKCtOG9ki03TzkaY4KvP5Qi b2P8nDExdngSPupA3R0ZDqqFFtsHvJkByTJuTJLcGPZHBciFABaj++ybVHlP+TXtPdTN aNLw== X-Gm-Message-State: AIVw113/DTIrY/E78tRZNuKN3H7Y1x05MoOePvSdU3M7/jG2kNSR89Wt XVVVDaT2uM2boh72 X-Received: by 10.98.66.90 with SMTP id p87mr1073153pfa.21.1501091362790; Wed, 26 Jul 2017 10:49:22 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.168.193 with SMTP id e62ls1000279ioj.6.gmail; Wed, 26 Jul 2017 10:49:21 -0700 (PDT) X-Received: by 10.36.80.193 with SMTP id m184mr58177itb.6.1501091361485; Wed, 26 Jul 2017 10:49:21 -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:33349 Archived-At: ------=_Part_3512_1575275533.1501091360807 Content-Type: multipart/alternative; boundary="----=_Part_3513_1907833215.1501091360807" ------=_Part_3513_1907833215.1501091360807 Content-Type: text/plain; charset="UTF-8" On Wednesday, July 26, 2017 at 1:10:26 PM UTC-4, Zhihao Yuan wrote: > > On Jul 26, 2017 5:18 AM, "d25f...@outlook.com " < > d25f...@outlook.com > wrote: > > > By "initialization order", I was trying to mean "the order the > designated initializers are listed", not "the order the class' member > variables are initialized". Sorry for the misleading term. > > What I tried to mean is that we can "repeat the mistake" and initialize > the object using the order its members are declared, regardless the > order the designated initializers are listed, and leaves the compiler to > warn the user if appropriate. We can also allow the user to suppress the > warning using some attribute on his will. > > Still, even if it's a mistake for mem-init-clause, for the third party > structures whose definition cannot be controlled by us, the "severity of > the mistake" is mitigated. > > > The severity of the mistake is increased. > You essentially get a feature to > encourage silently breaking users' > legitimate code which relies on a > specific evaluation order of the > initializers by changing the member > declaration order at the library side. > > I think another way to look at it is this. Designated initializers are just a convenience form of aggregate initialization (one that notably allows you to skip members and let them be initialized via their default member initializers). If you couldn't guarantee the order of the items in the struct, then you couldn't use aggregate initialization to begin with. And thus, you shouldn't be surprised that you can't use designated initializers. Initializing members out-of-order through aggregate initialization would be a new thing, not a convenience feature. -- 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/ad912456-47bb-4775-bb49-8750682efd5d%40isocpp.org. ------=_Part_3513_1907833215.1501091360807 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Wednesday, July 26, 2017 at 1:10:26 PM UTC-4, Z= hihao Yuan wrote:
On Jul 26, 2017 5:18 AM, "d25f...= @outlook.com" <d25f...@outlook.com> wrote:
By "initialization order", I was trying to mean "the order t= he
designated initializers are listed", not "the order the class'= ; member
variables are initialized". Sorry for the misleading term.

What I tried to mean is that we can "repeat the mistake" and init= ialize
the object using the order its members are declared, regardless the
order the designated initializers are listed, and leaves the compiler to warn the user if appropriate. We can also allow the user to suppress the warning using some attribute on his will.

Still, even if it's a mistake for mem-init-clause, for the third party<= br> structures whose definition cannot be controlled by us, the "severity = of
the mistake" is mitigated.

The severity of the mistake is increased.<= /div>
You essentially get a feature to
encourage silently breaking users'
legitimat= e code which relies on a
specific evaluation order o= f the
initializers by changing the member
declaration order at the library side.


I think another way to look at it is this. Designated initial= izers are just a convenience form of aggregate=20 initialization (one that notably allows you to skip members and let them be initialized via their default member initializers). If you couldn't= guarantee the order of the items in the struct, then you couldn't use = aggregate initialization to begin with.=C2=A0 And thus, you shouldn't b= e surprised that you can't use designated initializers.

Initiali= zing members out-of-order through aggregate initialization would be a new t= hing, not a convenience feature.

--
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/ad912456-47bb-4775-bb49-8750682efd5d= %40isocpp.org.
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