220 41233 article Path: news.gmane.org!.POSTED!not-for-mail From: Tom Honermann Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Modules and preambule, just why? Date: Thu, 6 Dec 2018 11:16:04 -0500 Lines: 164 Approved: news@gmane.org Message-ID: References: <16989401-2f0d-4200-997e-0ac60b47bec3@isocpp.org> <08290107-c63b-3ef6-09d4-16c7b6c495ab@honermann.net> <0727d34e-0bad-3689-e315-2136bb359e65@honermann.net> <41ef0549-4ff9-4d0d-b033-5eb30055490c@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------066FFB0FA5943E0A7D6C1194" X-Trace: blaine.gmane.org 1544112843 23536 195.159.176.226 (6 Dec 2018 16:14:03 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 6 Dec 2018 16:14:03 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 Cc: ville.voutilainen@gmail.com To: std-proposals@isocpp.org, Victor Dyachenko Original-X-From: std-proposals+bncBDBNXSHG6UDBBRUWUXQAKGQEFEIN74A@isocpp.org Thu Dec 06 17:13:58 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-io1-f71.google.com ([209.85.166.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gUwHl-0005xh-8X for gclcip-std-proposals@m.gmane.org; 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[184.106.54.107]) by mx.google.com with ESMTPS id i8si334910ioh.24.2018.12.06.08.16.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 06 Dec 2018 08:16:05 -0800 (PST) Received-SPF: pass (google.com: domain of tom@honermann.net designates 184.106.54.107 as permitted sender) client-ip=184.106.54.107; Original-Received: from smtp22.relay.ord1d.emailsrvr.com (localhost [127.0.0.1]) by smtp22.relay.ord1d.emailsrvr.com (SMTP Server) with ESMTP id 6858CE06AF; Thu, 6 Dec 2018 11:16:05 -0500 (EST) X-Auth-ID: tom@honermann.net Original-Received: by smtp22.relay.ord1d.emailsrvr.com (Authenticated sender: tom-AT-honermann.net) with ESMTPSA id 13E39E06B3; Thu, 6 Dec 2018 11:16:04 -0500 (EST) X-Sender-Id: tom@honermann.net Original-Received: from [192.168.1.19] (pool-71-176-235-158.rcmdva.fios.verizon.net [71.176.235.158]) (using TLSv1.2 with cipher AES128-SHA) by 0.0.0.0:25 (trex/5.7.12); Thu, 06 Dec 2018 11:16:05 -0500 In-Reply-To: <41ef0549-4ff9-4d0d-b033-5eb30055490c@isocpp.org> Content-Language: en-US X-Original-Sender: tom@honermann.net X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@honermann.net header.s=20180930-2j89z3ji header.b=bOLu1P90; spf=pass (google.com: domain of tom@honermann.net designates 184.106.54.107 as permitted sender) smtp.mailfrom=tom@honermann.net; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=honermann.net 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:41233 Archived-At: This is a multi-part message in MIME format. --------------066FFB0FA5943E0A7D6C1194 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable On 12/6/18 6:38 AM, Victor Dyachenko wrote: > On Thursday, December 6, 2018 at 7:05:01 AM UTC+3, Tom Honermann wrote: > > Hmm, Gaby has stated many times that .ifc files are not intended for > distribution. > > > Really? So what such modules are supposed to be? Yet another=20 > reincarnation of precompiled headers? I think of them as being very much like precompiled headers with a few=20 additions: 1. Entities that can't be defined in headers without leading to duplicate definition problems (e.g., non-template function definitions) can be present in module interface units. Compilation of the module interface unit emits such entities to a separate object file (that must be linked in somewhere). 2. Macro containment. 3. Protection against order of include/import problems. 4. Protection against name collisions. > > And why gcc and clang developers are trying "to define interoperable=20 > changes" (see https://gcc.gnu.org/wiki/cxx-modules) and establish=20 > stable ABI=20 > (https://gcc.gnu.org/wiki/cxx-modules?action=3DAttachFile&do=3Dview&targe= t=3Dmodule-abi-2017-09-01.pdf)? The changes referred to in those links concern ABI (primarily name=20 mangling), not portability of module artifacts.=C2=A0 The intent of the ABI= =20 compatibility is to enable objects/libraries compiled with different=20 compilers to be able to be linked together in a single program.=C2=A0 Such= =20 compatibility does not extend to module artifacts used at compile-time. Here is a quote from the second link: "It is taken as axiomatic that the BMI is generated by the same compiler=20 that compiles any TUs importing the module. As such, it can conspire to step outside the ABI,=20 where such behavior could not be observed by other TUs." I believe that should be read as "by the same installation of the=20 compiler" or, minimally, the same version. Tom. --=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/da76c6e9-93a2-262f-f5dd-e104140dd13a%40honermann= ..net. --------------066FFB0FA5943E0A7D6C1194 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On 12/6/18 6:38 AM, Victor Dyachenko wrote:
On Thursday, December 6, 2018 at 7:05:01 AM UTC+3, Tom Honermann wrote:
Hmm, Gaby has stated many times that .ifc files are not intended for
distribution.=C2=A0

Really? So what such modules are supposed to be? Yet another reincarnation of precompiled headers?

I think of them as being very much like precompiled headers with a few additions:

  1. Entities that can't be defined in headers without leading to duplicate definition problems (e.g., non-template function definitions) can be present in module interface units.=C2=A0 Compilation of the module interface unit emits such entities to a separate object file (that must be linked in somewhere).
  2. Macro containment.
  3. Protection against order of include/import problems.
  4. Protection against name collisions.

And why gcc and clang developers are trying "to define interoperable changes" (see https://gcc.gnu.org/wiki/cxx-modules) and establish sta= ble ABI (https://gcc.gnu.org/wiki/cxx-modules?action=3DAttachFile&do=3Dview= &target=3Dmodule-abi-2017-09-01.pdf)?

The changes referred to in those links concern ABI (primarily name mangling), not portability of module artifacts.=C2=A0 The intent of the ABI compatibility is to enable objects/libraries compiled with different compilers to be able to be linked together in a single program.=C2=A0 Such compatibility does not extend to module artifacts used at compile-time.

Here is a quote from the second link:

"It is taken as axiomatic that the BMI is generated by the same compiler that compiles any TUs
importing the module. As such, it can conspire to step outside the ABI, where such behavior could not
be observed by other TUs."

I believe that should be read as "by the same installation of the compiler" or, minimally, the same version.

Tom.

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