220 35134 article Path: news.gmane.org!.POSTED!not-for-mail From: Giovanni Piero Deretta Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Lookup in if constexpr discarded substatement Date: Mon, 30 Oct 2017 07:17:17 -0700 (PDT) Lines: 112 Approved: news@gmane.org Message-ID: References: <05ed746c-e02b-410f-a0f7-1800ab5fbc11@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_6671_827955059.1509373037607" X-Trace: blaine.gmane.org 1509373042 30459 195.159.176.226 (30 Oct 2017 14:17:22 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 30 Oct 2017 14:17:22 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDEP3I7TGEIO52G4Z4CRUBDAPKSX4@isocpp.org Mon Oct 30 15:17:13 2017 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 1e9AsK-00070Q-Mb for gclcip-std-proposals@m.gmane.org; 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Mon, 30 Oct 2017 07:17:19 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.115.6 with SMTP id o6ls3368397vkc.14.gmail; Mon, 30 Oct 2017 07:17:18 -0700 (PDT) X-Received: by 10.31.96.146 with SMTP id u140mr1626709vkb.2.1509373038186; Mon, 30 Oct 2017 07:17:18 -0700 (PDT) In-Reply-To: <05ed746c-e02b-410f-a0f7-1800ab5fbc11@isocpp.org> X-Original-Sender: gpderetta@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:35134 Archived-At: ------=_Part_6671_827955059.1509373037607 Content-Type: multipart/alternative; boundary="----=_Part_6672_848649576.1509373037608" ------=_Part_6672_848649576.1509373037608 Content-Type: text/plain; charset="UTF-8" On Wednesday, October 25, 2017 at 1:39:53 PM UTC+1, Corentin wrote: > > Hello. > > Currently, the discarded if-constexpr sub-statements are fully parsed, > including name-lookup. > Not performing name lookup, or ignoring name lookup failure within > discarded statements could help get rid of some `#ifdef` macros, improving > readability and, more importantly, tooling. > > > void f() { > if constexpr(false) { > UndeclaredMethod(); > } > } > > I think that the discarded blocks should still be parsed and contain valid > syntax. Tooling can, for example, rename symbols within these statements, > whereas it can't inspect disabled `#ifdef` blocks without re-running the > processor. > > > While playing with an orthogonal feature, I discovered that the MSVC > compiler has a keyword to disable a block of code if a particular symbol > does not exist https://msdn.microsoft.com/en-us/library/x7wy9xh3.aspx > However, I believe modifying `if constexpr` semantic would be a more > powerful and generic solution. > > > What do you think ? > -- 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/ff377bea-cbde-4ea4-a4f2-72266e163727%40isocpp.org. ------=_Part_6672_848649576.1509373037608 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Wednesday, October 25, 2017 at 1:39:53 PM UTC+1= , Corentin wrote:
Hello.

Currently, the discarded if-constexpr sub-sta= tements are fully parsed, including name-lookup.
Not performing n= ame lookup, or ignoring name lookup failure within discarded statements=C2= =A0 could help get rid of some `#ifdef` macros, improving readability and, = more importantly, tooling.


void f() {
=C2=A0 =C2=A0if constexpr(false) {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 UndeclaredMethod();
=C2=A0 =C2=A0}=
}

= I think that the discarded blocks should still be parsed and contain valid = syntax.=C2=A0 Tooling can, for example, rename symbols within these stateme= nts, whereas it can't inspect disabled `#ifdef` blocks without re-runni= ng the processor.


While playing with an orthog= onal feature, I discovered that the MSVC compiler has a keyword to disable = a block of code if a particular symbol does not exist=C2=A0https= ://msdn.microsoft.com/en-us/library/x7wy9xh3.aspx=C2=A0 Howev= er, I believe modifying `if constexpr` semantic would be a more powerful an= d generic solution.


What do you thi= nk ?

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