220 29140 article Path: news.gmane.org!.POSTED!not-for-mail From: Aaron McDaid Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: pragma once Date: Wed, 26 Oct 2016 14:48:53 -0700 (PDT) Lines: 149 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_0_2021283399.1477518533838" X-Trace: blaine.gmane.org 1477518562 18722 195.159.176.226 (26 Oct 2016 21:49:22 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 26 Oct 2016 21:49:22 +0000 (UTC) Cc: sergeikrivonos@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCE67KWO5UEBBR6JYTAAKGQETNI3P4Q@isocpp.org Wed Oct 26 23:49:17 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f70.google.com ([209.85.218.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bzW4A-0001pq-0z for gclcip-std-proposals@m.gmane.org; Wed, 26 Oct 2016 23:48:58 +0200 Original-Received: by mail-oi0-f70.google.com with SMTP id n202sf17716585oig.3 for ; Wed, 26 Oct 2016 14:49:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version: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=f4jaa4Ktf7xXhM+63i1VGxsgaLqBextXMsg6LWXPa44=; b=uptGxebHHwZXXyX6CQxFQnRSGr+gx6OYGHEFNcNe9ogQ+df5D1TM8E1nE3XsML1nmm 6kJta53zP0/z0/GeX9UYgiimTK6vO1Bvru+paPaTatAwRB/anCzNkGA5U0vRZl5eE88a m23m0LhenkVHX/59O+WLEnkFth3+Bei5DJvu5QxtqLbvlnjrQ+mSLBmSDAgt6SwAaYV3 KptpL1LGfUQA6AyRhdxoujdN4Uj4kawBtBcE4A+jKqulsxxhkFlXFlw0BieJw0VAdspj Mk3bxsHXjn4/aGPHyRNAYwOhOkLF9rktTilRtS+nt18x2tnD9m7bPDBX5wj3R5FWQVAU 2SMQ== 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: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=f4jaa4Ktf7xXhM+63i1VGxsgaLqBextXMsg6LWXPa44=; b=OgUcvk5mWYNNq4XApi/aFwi60+xXjVTRj8dBeEwA1DSm8swo0EMaAL2kVIM7VmZZ+w YTI3xkwonUGV/CiStcmSjfy9XUIj0tAfBrFJvJq88ZxwvvwnqWrMDEvDI0O3UtLgDsGd tV+wlwd2WdjlWp+iDFZ67Kdi6Og71TyDQnE3gm9AESsYI0c5fV6o1Pt+9Tab+hJT+z7q YtIW0At1TROl1uyWt00fL9CUruKJ6iZcLXGyMyHgD7ed1dBIRHUa/R+eVEwPRzaalCAK dwe+Cmn0gZ9WmJBB8nWhGO74iRlKkdboLQ5omVW2pqiBoQD/J7OcdJWDsM8Lt6aCkw54 A5kQ== 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: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=f4jaa4Ktf7xXhM+63i1VGxsgaLqBextXMsg6LWXPa44=; b=FphB3QTFn06sMoEuS3olejGQfXHGeIetojypK4wQDC1D1JVLdpMcWmOfpgaMkdaCxw FTLVz7Ptjw94b9KGDhSGOTD7rl62kUeZykFt8IaoSFiGQo/LAHWxxbh59RqT2gxY758E zjS/22PaIcBAlgcG9BW/LTJm4r45/nzLxBkyDbPITKOzKYjmwbqYztiD9Q3IL0Mt12pj WD8/PSbJePDPDx9Okq+Kjf7Dv5tzdLKQL9NsBv/JB6g1KnLAyZTD2z5ltSEPSzAgU0+X YGr9X1A6CNpc6Ex0K7vXEuS7keWQY6quZ6mOM113Fp2MtGlK+CO1EX8WPYQEb15sBdsW Btpg== X-Gm-Message-State: ABUngvcB5B6sGX9awmC0b9429T2uWusIim6ov5NyW/4PH6CVXeNfSsBuXur9OD1xzOR2RQ== X-Received: by 10.157.1.15 with SMTP id 15mr1558216otu.147.1477518540283; Wed, 26 Oct 2016 14:49:00 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.178.80 with SMTP id b77ls694183iof.47.gmail; Wed, 26 Oct 2016 14:48:55 -0700 (PDT) X-Received: by 10.36.26.212 with SMTP id 203mr765916iti.2.1477518535552; Wed, 26 Oct 2016 14:48:55 -0700 (PDT) In-Reply-To: X-Original-Sender: aaronmcdaid@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:29140 Archived-At: ------=_Part_0_2021283399.1477518533838 Content-Type: multipart/alternative; boundary="----=_Part_1_1609139446.1477518533846" ------=_Part_1_1609139446.1477518533846 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi all, I'd like to join this conversation by asking everybody to "reset" a little.= =20 There is no reason whatsoever to think that we need to get distracted about= =20 filesystem issues. Also, frankly, the tone of some commentators here is very arrogant. This is= =20 my first time in an isocpp.org forum and I'm already not impressed with the= =20 community. When '#include' is encountered, the compiler will use some arbitrary=20 mechanism to convert the included "pseudo-file-name" into a long string of= =20 characters. One possible proposal is that, once that long string is fully= =20 read it, it will be hashed. If a given hash has been encountered before,=20 and the first characters of the long string are `#pragma once`, then only= =20 the first include will be retained. That's simple to understand and to define precisely in the standard. I=20 guess it's just a tweak of Phase 4 of the translation phases:=20 http://en.cppreference.com/w/cpp/language/translation_phases I do not know, nor care, whether the behaviour I have just defined is=20 equivalent to the behaviour currently in any compiler. If there is a subtle= =20 difference in some extreme case, then I don't care. Are you including two= =20 different files with the same contents? If so, I don't care if we change=20 the behaviour a little! There needn't be a speed issue. A naive implemention would be forced to=20 read in all of the header file before processing any of it. But it would be= =20 easy to optimize this with a little "lookahead" to confirm that a given=20 included-file is indeed novel and therefore the compiler can proceed with= =20 'single-pass' compilation. Of course, maybe there is some issue I have overlooked. I'm not claiming to= =20 be perfect, but I do believe I'm not the only person who thinks '#pragma=20 once' could be standardized in some form if we just showed a little=20 imagination. If this has been argued to death before, please provide links to the=20 discussion to prove=20 Aaron On Tuesday, 25 October 2016 08:15:55 UTC+2, =D0=A1=D0=B5=D1=80=D0=B3=D0=B5= =D0=B9 =D0=9A=D1=80=D0=B8=D0=B2=D0=BE=D0=BD=D0=BE=D1=81 wrote: > > Hi, > > I see everyone use ifdef or pragma once. It is better to use #pragma=20 > multiple and make #pragma once default. > > --=20 > Thanks > Sergei Krivonos > skype: sergio_krivonos > --=20 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 e= mail 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/e417071f-3473-4d64-8f5d-6e45909acde7%40isocpp.or= g. ------=_Part_1_1609139446.1477518533846 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hi all,
I'd like to join this conversation by askin= g everybody to "reset" a little. There is no reason whatsoever to= think that we need to get distracted about filesystem issues.

Also,= frankly, the tone of some commentators here is very arrogant. This is my f= irst time in an isocpp.org forum and I'm already not impressed with the= community.


When '#include' is encountered, the compiler= will use some arbitrary mechanism to convert the included "pseudo-fil= e-name" into a long string of characters. One possible proposal is tha= t, once that long string is fully read it, it will be hashed. If a given ha= sh has been encountered before, and the first characters of the long string= are `#pragma once`, then only the first include will be retained.

T= hat's simple to understand and to define precisely in the standard. I g= uess it's just a tweak of Phase 4 of the translation phases: http://en.= cppreference.com/w/cpp/language/translation_phases

I do not know, no= r care, whether the behaviour I have just defined is equivalent to the beha= viour currently in any compiler. If there is a subtle difference in some ex= treme case, then I don't care. Are you including two different files wi= th the same contents? If so, I don't care if we change the behaviour a = little!

There needn't be a speed issue. A naive implemention wou= ld be forced to read in all of the header file before processing any of it.= But it would be easy to optimize this with a little "lookahead" = to confirm that a given included-file is indeed novel and therefore the com= piler can proceed with 'single-pass' compilation.

Of course,= maybe there is some issue I have overlooked. I'm not claiming to be pe= rfect, but I do believe I'm not the only person who thinks '#pragma= once' could be standardized in some form if we just showed a little im= agination.

If this has been argued to death before, please provide l= inks to the discussion to prove

Aaron

On Tuesday, 25 October= 2016 08:15:55 UTC+2, =D0=A1=D0=B5=D1=80=D0=B3=D0=B5=D0=B9 =D0=9A=D1=80=D0= =B8=D0=B2=D0=BE=D0=BD=D0=BE=D1=81 wrote:
Hi,

I see everyone use ifdef= or pragma once. It is better to use #pragma multiple and make #pragma once= default.

--
Thanks
Sergei Kriv= onos
skype: sergio_krivonos

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
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/e417071f-3473-4d64-8f5d-6e45909acde7= %40isocpp.org.
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