220 20786 article Path: news.gmane.org!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Null -conditional and -coalescing operators Date: Thu, 24 Sep 2015 12:51:02 -0700 (PDT) Lines: 135 Approved: news@gmane.org Message-ID: References: <4c3e2ee7-2159-4e93-a439-7d5c94c38c9c@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1062_489372124.1443124262460" X-Trace: ger.gmane.org 1443124267 22605 80.91.229.3 (24 Sep 2015 19:51:07 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 24 Sep 2015 19:51:07 +0000 (UTC) Cc: mwoehlke.floss@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBKFISGYAKGQEODDQMCI@isocpp.org Thu Sep 24 21:51:06 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f200.google.com ([209.85.214.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZfCXq-0006Ds-0B for gclcip-std-proposals@m.gmane.org; Thu, 24 Sep 2015 21:51:06 +0200 Original-Received: by obbgf5 with SMTP id gf5sf117991082obb.3 for ; Thu, 24 Sep 2015 12:51:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:content-type: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=0EV0eGM/uC+twI3WHM/Gl+Li66BqhrqE/XdfJN/ktEw=; b=gkOpakzA6Ys2Ds3bIcIJRLOYVilTjyW2/uSvjlwbKgmWzBxouioJNR+Yms0gKsOrrx ushoqxudgKY14OScZetlCVWKEn0Ht2GY+AtPqBTzhjFuNYunzKjr4Z3B8ajLpbAKxaoV tH3BMLYVjUU13Y9ZS3f9JLqf6Vw5R0BBvtqgg3SIWp9KNkKleNjSoTMrkG1cplTdt9Tp MiuxMxrHm9j24srGbu8BHbel07qwCMTOF1X2vtvAXJzY1rladTorCP6X/cFUeJMEoLZT skeHQm3g9xra13SDQMucHU047qGT0WO7pW9Kr3mQNYPZ3lFTQ3IrVOStmCt607DT/CHH 55Fg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:content-type: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=0EV0eGM/uC+twI3WHM/Gl+Li66BqhrqE/XdfJN/ktEw=; b=TddwnITorUi/T4e+iwDY/C6QT98LEKQmzjptDaZT/lmHaiZBW9A1o7YA9YGkCuxDXy adyC+2Lvzq8tzHDo4F4MzS4gvKh+n/+hOowWXU+CAxJqp7WiR+xcGzI5d50ocoTgG6X3 No3K7HUm1QESfUcZ1qvRTsM4YS6k0Cys4riBGdKnnXh2DzXeuwKTuMhFIlEWxvyFa261 tU7xaBF0aICPTmP8mnOmlF3uKCQRRmxKTObMIqcTY1tG4oG08cAfgTYc5D9zKe51J7Sy lsRThn7f2fCpuH9QELareaR4x50AlNFeMTP3RD08XYut/7kgOzceoKpHiUDfoSD3BLSi 3SBw== X-Gm-Message-State: ALoCoQky+W/JNSB4K0fU79V3976IjNxEjJLi1yS4CAWkfnjt9nHFgIR2WjvVKr8kIzhwvFx/yhDS X-Received: by 10.182.106.11 with SMTP id gq11mr1277519obb.25.1443124265027; Thu, 24 Sep 2015 12:51:05 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.60.34 with SMTP id e2ls19947igr.4.canary; Thu, 24 Sep 2015 12:51:04 -0700 (PDT) X-Received: by 10.50.117.4 with SMTP id ka4mr156772igb.6.1443124264338; Thu, 24 Sep 2015 12:51:04 -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-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:20786 Archived-At: ------=_Part_1062_489372124.1443124262460 Content-Type: multipart/alternative; boundary="----=_Part_1063_960156838.1443124262460" ------=_Part_1063_960156838.1443124262460 Content-Type: text/plain; charset=UTF-8 On Thursday, September 24, 2015 at 10:36:06 AM UTC-4, Matthew Woehlke wrote: written += ?(stream)->write(buffer); > That brings up a question. Namely... what does that actually do? What I mean is this: `?(stream)->write(buffer)` is an expression. What type does it resolve to? The general idea with these things is that they resolve to doing something or not doing something. And thus, is equivalent to: if(stream) then stream->write(buffer) But that's not an expression; that's a statement. Statements don't resolve to values. So if the condition is false, what does the overall expression resolve to? Does it default-construct a value of the type that would result if the condition was true? Or does the condition being false completely wipe out the entire statement. That is, even the += is part of the condition. If so, that requires look-ahead. Potentially *lots* of look-ahead. ?: makes it clear exactly what's going on: written += stream ? stream->write(buffer) : 0; (I'll note that part of the motivation here probably comes from wanting > to dodge draconian coding styles that mandate multiline braces around > ANY conditional body. Which, I'll be honest, I've done myself... > employed ugly hacks to dodge such, I mean; I personally loathe requiring > braces in single-statement conditional bodies.) > That's a pretty poor motivation for a language 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_1063_960156838.1443124262460 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Thursday, September 24, 2015 at 10:36:06 AM UTC-4, Matt= hew Woehlke wrote:

written +=3D ?(stream)->write(buffer);
That brings up a question. Namely... what does that actually do?

Wh= at I mean is this: `?(stream)->write(buffer)` is an expression. What typ= e does it resolve to? The general idea with these things is that they resol= ve to doing something or not doing something. And thus, is equivalent to:
if(stream) then stream->write(buffer)<= /span>
=

But that's not an expression; that's a state= ment. Statements don't resolve to values.

So if the condition is= false, what does the overall expression resolve to? Does it default-constr= uct a value of the type that would result if the condition was true?
Or does the condition being false completely wipe out the entire statement= .. That is, even the +=3D is part of the condition. If so, that requires loo= k-ahead. Potentially lots of look-ahead.

?: makes it clear ex= actly what's going on:

written +=3D stream ? stream->w= rite(buffer) : 0;

(I'll note that part of the motivation here probably = comes from wanting
to dodge draconian coding styles that mandate multiline braces around
ANY conditional body. Which, I'll be honest, I've done myself..= ..
employed ugly hacks to dodge such, I mean; I personally loathe requirin= g
braces in single-statement conditional bodies.)

That's a pretty poor motivation for a languag= e feature.

--

---
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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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