220 29225 <75abf111-7808-84df-be82-6fddcd5d1e8c@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Andrey Semashev Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: [RFC] #pragma once... yes, really... 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[90.154.68.136]) by smtp.googlemail.com with ESMTPSA id h99sm2277889lji.39.2016.10.28.14.00.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 28 Oct 2016 14:00:26 -0700 (PDT) In-Reply-To: <28223b1b-dd80-4055-acb0-aef52b6a228d@isocpp.org> X-Original-Sender: andrey.semashev@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of andrey.semashev@gmail.com designates 2a00:1450:4010:c07::242 as permitted sender) smtp.mailfrom=andrey.semashev@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:29225 Archived-At: On 10/28/16 23:46, T. C. wrote: > > > On Friday, October 28, 2016 at 4:33:23 PM UTC-4, Matthew Woehlke > wrote:On 2016-10-28 16:01, T. C. wrote: > > > #pragma once (std :: vector :: foo :: bar :: 1.0). > > > > Where does the "qualified C++ identifier" end and where does > "version" > > begin? > > Um... I think this would be an error; `1.0` isn't a valid identifier. > > > > > Or are you saying that unlike actual "qualified C++ identifier"s, > > you can't have whitespace here? > > I wasn't thinking about whitespace, actually... Okay, I see the > problem: > > #once hello ::world > > If we allow whitespace between 'parts' of the name, is that 'hello', > version '::world', or 'hello::world' with no version? > > That's easy to fix; forbid the version starting with `:`. Maybe the > version doesn't even need `:`; that usually only shows up in > distribution package versions for unusual reasons related to > distribution packaging (that delve into the horribly complicated realm > of version number sorting). > > I believe this makes the parsing simple: whitespace followed by > not-a-`:` separates the version from the name. Then we can also allow > (and ignore) whitespace around `::`. > > Note: the version may *not* contain whitespace. > > > That may work, but "version" as described can be several preprocessing > tokens (1.0.1-1 is three: "1.0.1", "-", "1"), so you either need a > special rule that says there can't be whitespace between those pp-tokens > (unlike most other cases), or introduce a new type of preprocessing > token formed only in #once, like header-names. Neither approach sounds > particularly appealing to me compared to just using a string-literal. Maybe just make the version an unsigned integer? -- 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/75abf111-7808-84df-be82-6fddcd5d1e8c%40gmail.com. .