220 20639 <49724df9-5491-4466-bf18-818e14c9dda9@isocpp.org> article Path: news.gmane.org!not-for-mail From: joewoodbury@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Null -conditional and -coalescing operators Date: Tue, 22 Sep 2015 11:41:49 -0700 (PDT) Lines: 149 Approved: news@gmane.org Message-ID: <49724df9-5491-4466-bf18-818e14c9dda9@isocpp.org> 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_6_1670467107.1442947309489" X-Trace: ger.gmane.org 1442947314 2676 80.91.229.3 (22 Sep 2015 18:41:54 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 22 Sep 2015 18:41:54 +0000 (UTC) Cc: mwoehlke.floss@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCBMHLUN7EEBB3WBQ2YAKGQESROCBDY@isocpp.org Tue Sep 22 20:41:54 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f199.google.com ([209.85.213.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZeSVl-0007ko-92 for gclcip-std-proposals@m.gmane.org; Tue, 22 Sep 2015 20:41:53 +0200 Original-Received: by igbbp9 with SMTP id bp9sf44470081igb.3 for ; Tue, 22 Sep 2015 11:41:52 -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=If5kYgr/n4OjNnrro2JQtZFLronVy4NVF7qV5wSLI+I=; b=jusiu9pHtkX3PsZL6QCULu283ixquVVKVc/zbKOFLt7wxmtaQCiKbPrwoJ02Zwwcc4 BckXmh3FfMrE0LP6Ifa+yaMlEY7U/vZQ7jyjgMOYXsTcJFbFov4YOa4u8GrGUDY2WVaD ysAQryu0zG8F9SIf86Ra1+PhL2hRCUmOu8t/T4w5ThSTltFXs40SOUs126A5HOj41lxQ 6L+dDs4pAI0Kub0ewbLx7Bj6W6YFftQtG6Z50/VFjOhoneINrblPkl/1bhU8vK0GKZKj x7GOL9Ol3U193Q8P9AsiWVegrJRRRKpAALxa1GLSJdfsMjlU+fdBIw0nLCtZB01NU9tc 9Ldg== 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=If5kYgr/n4OjNnrro2JQtZFLronVy4NVF7qV5wSLI+I=; b=YTRCJcGdKVUvqNjIYBwsrGZE/NjTN5vIZQ2VrfO5zjQVjg/MX+9FFgkAHSMiEcIC2l jyWC6fdXKeza6Sz7bOcvNZLXDyOUR0ny2lHsceFtj2uDL1VMZ9nnAVFHEYYmueUwKIam QoEeb13Zyuwqf8EKB9BAd8yDfNPpNz2OOTXm+5msY0q+qNRe50NFIhP8HlKexVnhBW7j UzweoiGboXsI5ZmvoR4+MuazfBhubo+RK626gfLK+Zgai9Mul/kMzTe2PAEzTlPvYE0g hD+amhcs2XOzuL35WaNRAcUh5/hzjPgjEH1VL+dWcc3HdHrqqO1xGx/NSBCBL48YwBvP s3lg== X-Gm-Message-State: ALoCoQmpTjAzq1L1eE7J4pgsIBUgTy76qTm3qjfFqJ4NY5e98F3ZCJzhYEF51dyNNPP6yEQ7EKfl X-Received: by 10.182.149.168 with SMTP id ub8mr22493382obb.30.1442947312056; Tue, 22 Sep 2015 11:41:52 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.62.4 with SMTP id u4ls239894igr.21.gmail; Tue, 22 Sep 2015 11:41:50 -0700 (PDT) X-Received: by 10.50.147.100 with SMTP id tj4mr215290igb.2.1442947310202; Tue, 22 Sep 2015 11:41:50 -0700 (PDT) In-Reply-To: X-Original-Sender: joewoodbury@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:20639 Archived-At: ------=_Part_6_1670467107.1442947309489 Content-Type: multipart/alternative; boundary="----=_Part_7_1948381328.1442947309489" ------=_Part_7_1948381328.1442947309489 Content-Type: text/plain; charset=UTF-8 My mistake. I had collapsed several examples in order to keep my message short and in the process created a bogus example. I apologize. I had been considering a recent bug where a reference had "contained" a nullptr (not in my code!) and wondered if this could be a solution. I was thinking of another spot of code where an overloaded operator is returning either a nullptr or valid pointer. If the former, it assigns another value to lvalue. On Tuesday, September 22, 2015 at 10:38:35 AM UTC-7, Matthew Woehlke wrote: > > On 2015-09-22 13:03, joewo...@gmail.com wrote: > > Checking for null and then doing one thing is a common task. > > > > bool success = connection ?: false; > > That makes no sense; you are assigning the value 'false' to 'success' if > 'connection' "is true", but what if it is false? Then what? Nor does it > make sense for the declaration to be conditional. > > Rather, you would need to write something like: > > bool success = connection ? false : true; > > ...which you can do already. Or just use the converted value directly, > as Nicol notes. > > > connection?->SendMessage(msg); > > I think the syntax ought to be more like: > > ?(connection)->SendMessage(msg); > > ...where '?(expr)' says to evaluate the truth-value of 'expr' and, if > true, "return" 'expr', otherwise skip the statement. (I'd avoid 'expr?' > as it seems likely to make parsing that vs. 'expr?expr:expr' difficult. > Plus, one would expect 'expr?expr' to act more like the trinary, just > without the ':expr' part, and not "reuse" the LHS expression.) > > You could also write things like: > > x = ?(y); // if (y) x = y; > > However, this is a very unusual construct for questionable gain. > > -- > Matthew > > -- --- 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_7_1948381328.1442947309489 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
My mistake. I had collapsed several examples in order to k= eep my message short and in the process created a bogus example. I apologiz= e.

I had been considering a recent bug where a reference had "c= ontained" a nullptr (not in my code!) and wondered if this could be a = solution.

I was thinking of another spot of code where an overloaded= operator is returning either a nullptr or valid pointer. If the former, it= assigns another value to lvalue.



On Tuesday, September 22, = 2015 at 10:38:35 AM UTC-7, Matthew Woehlke wrote:
On 2015-09-22 13:03, joewo...@gmail.com wrote:
> Checking for null and then doing one thing is a common task.=20
>=20
> =C2=A0 =C2=A0 bool success =3D connection ?: false;

That makes no sense; you are assigning the value 'false' to = 9;success' if
'connection' "is true", but what if it is false? Then= what? Nor does it
make sense for the declaration to be conditional.

Rather, you would need to write something like:

=C2=A0 bool success =3D connection ? false : true;

...which you can do already. Or just use the converted value directly,
as Nicol notes.

> =C2=A0 =C2=A0 connection?->SendMessage(msg);

I think the syntax ought to be more like:

=C2=A0 ?(connection)->SendMessage(msg);

...where '?(expr)' says to evaluate the truth-value of 'exp= r' and, if
true, "return" 'expr', otherwise skip the statement. = (I'd avoid 'expr?'
as it seems likely to make parsing that vs. 'expr?expr:expr' di= fficult.
Plus, one would expect 'expr?expr' to act more like the trinary= , just
without the ':expr' part, and not "reuse" the LHS exp= ression.)

You could also write things like:

=C2=A0 x =3D ?(y); // if (y) x =3D y;

However, this is a very unusual construct for questionable gain.

--=20
Matthew

--

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