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[209.85.220.41]) by mx.google.com with SMTPS id x195sor2988473vkd.27.2018.11.28.03.16.51 for (Google Transport Security); Wed, 28 Nov 2018 03:16:51 -0800 (PST) Received-SPF: pass (google.com: domain of mjklaim@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a1f:4301:: with SMTP id q1mr15245953vka.70.1543403811108; Wed, 28 Nov 2018 03:16:51 -0800 (PST) In-Reply-To: X-Original-Sender: mjklaim@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=MbpFl9lc; spf=pass (google.com: domain of mjklaim@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=mjklaim@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=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:41100 Archived-At: On Tue, 27 Nov 2018 at 22:10, wrote: > The way modules have been done, they require the sources files to declare= which module they implements and what they exports into a preambule. > To be honest, I don't really get why this was necessary. My understanding is that the main reason is that it helps tools know the dependencies without having to parse the rest of the C++ syntax. Build systems will have to check every source file in a first pass to quickly decide what have to be built, by making a dependency graph. This pass is simple if the information is easily locatable and with always a strict subset of possible C++ syntax. (also it's similar to other module system from other languages, but that's not a reason). > Moreover, i found some drawbacks with it: > - It makes sources files dependent on which modules they will be shipped = in. I'm not sure I understand this point. Isn't it the point of modules to associate a module name to sources? > - Not only the sources does declare the module they belongs to, but they = also need to be put together in the build system (may it be Makefiles, cmak= e, ...). This goes against the DRY concept since it cause duplication of in= formation. I don't understand where would be a duplicate information. The module names exist only in sources, not in build system's project description files (at least in any decent build system). > - There is a concept of 'module interface unit' (and even a 'primary modu= le interface unit'!). As far as I understand it, it is almost the same that= old .h files, thus providing no real benefit over the latter when writing = new code. Of course it provides benefit! It's like saying that a header file and a module is similar, but it's really not. For example, your header will leak it's names into user's user's code. Modules will not by default. The point of these interface unit is to allow you to not change the interface but change the implementation without the user aving to recompile their code, even if all the module code is defined in one file. > > So, my question is why was this preambule necessary? Can't we avoid it? I'm not an expert, but I believe it is necessary if we want something that is easy to implement and works well with human readers. > Also there seems to be a paper which indicate that preambules are unnece= ssary (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1299r0.html= ). What's the status about this? This paper will be published very soon, but you can ask the author for a copy. Here is the revision 3's intro copy/pasted: --- Module Preamble is Unnecessarily Fragile Nathan Sidwell The ATOM proposal introduced the module preamble. The merged document modified that concept for increased flexibility. The rules determining the extent of the preamble have been modified, but it remains fragile. We should consider making the preamble more robust. TL;DR: This was presented to EWG at the San Diego=E2=80=9918 meeting. It wa= s accepted and is merged to p1103. ---- As you can see, it's a fix of the preamble, not a removal. A. Jo=C3=ABl Lamotte --=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/CAOU91OPMe-0PU7zEfKKPSQNMwtaf8cw%2Bq24XAes9pZTJq= PGrcg%40mail.gmail.com. .