220 37643 <0f06146e-ae61-4c74-b09d-07dae4aa058f@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Variable declaration in a ternary conditional Date: Wed, 4 Apr 2018 11:41:39 -0700 (PDT) Lines: 77 Approved: news@gmane.org Message-ID: <0f06146e-ae61-4c74-b09d-07dae4aa058f@isocpp.org> References: <8a755089-c146-47ab-8250-c2b3e705cacd@isocpp.org> <3cdd7b2c-3716-4a58-8a13-3f65fb2eae22@isocpp.org> <9fabc312-9500-4b34-9a4a-a2793891c585@isocpp.org> <820d844c-21a7-429c-bf55-17ee12f8ca8e@isocpp.org> <2fe5d081-e13f-4750-87b0-a3b5b47eb252@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_8_870928626.1522867300023" X-Trace: blaine.gmane.org 1522867177 11857 195.159.176.226 (4 Apr 2018 18:39:37 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 4 Apr 2018 18:39:37 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBZFYSTLAKGQETQPCERY@isocpp.org Wed Apr 04 20:39:32 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f69.google.com ([209.85.213.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1f3nJk-00030Y-Em for gclcip-std-proposals@m.gmane.org; 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Wed, 04 Apr 2018 11:41:41 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.162.133 with SMTP id l127ls2093775vke.13.gmail; Wed, 04 Apr 2018 11:41:40 -0700 (PDT) X-Received: by 10.31.140.138 with SMTP id o132mr2353554vkd.8.1522867300500; Wed, 04 Apr 2018 11:41:40 -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:37643 Archived-At: ------=_Part_8_870928626.1522867300023 Content-Type: multipart/alternative; boundary="----=_Part_9_1337700500.1522867300023" ------=_Part_9_1337700500.1522867300023 Content-Type: text/plain; charset="UTF-8" On Wednesday, April 4, 2018 at 2:23:43 PM UTC-4, Richard Hodges wrote: > > Just a thought, but how badly would it mangle the language if the if > keyword, as well as introducing a statement, was also able to introduce an > expression which returned: > > * In the case where there is an else clause: the std::common_type of its > true and false clauses > * In the case where there is no else clause: a std::optional where T is > the expression type of the true case. > I don't like the idea of implicitly tying syntax into a standard library type like `optional` in this way. We should just require that if-expressions have an `else` clause. Otherwise, the idea of an if-expression seems to be a solid one. This formulation also solves other problems; since it uses `if` as an introducer, it can use `if constexpr` as an introducer as well for `constexpr` initializations. -- 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/0f06146e-ae61-4c74-b09d-07dae4aa058f%40isocpp.org. ------=_Part_9_1337700500.1522867300023 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Wednesday, April 4, 2018 at 2:23:43 PM UTC-4, R= ichard Hodges wrote:
Just a thought, but how badly would it mangle the language if the = if keyword, as well as introduci= ng a statement, was also able to introduce an expression which returned:
* In the case where there is an else clause:=C2=A0 the std::common_typ= e of its true and false clauses
* In the case where there is no else cla= use: a std::optional<T> where T is the expression type of the true ca= se.

I don't like the idea of implicitly = tying syntax into a standard library type like `optional` in this way. We s= hould just require that if-expressions have an `else` clause.

Otherw= ise, the idea of an if-expression seems to be a solid one. This formulation= also solves other problems; since it uses `if` as an introducer, it can us= e `if constexpr` as an introducer as well for `constexpr` initializations.<= br>

--
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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.
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/0f06146e-ae61-4c74-b09d-07dae4aa058f= %40isocpp.org.
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