220 41388 article Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Andrey Semashev Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Improving compile times for non-template dependent member functions. Date: Wed, 23 Jan 2019 19:34:31 +0300 Approved: news@gmane.org Message-ID: References: <6a72db2a-932d-4f79-ab68-7c1424e93b9d@isocpp.org> Reply-To: std-proposals@isocpp.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="61190"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0.1 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCXY5TXHWYJRBG5PULRAKGQETKUGSZQ@isocpp.org Wed Jan 23 17:34:36 2019 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lj1-f198.google.com ([209.85.208.198]) by blaine.gmane.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.89) (envelope-from ) id 1gmLU4-000FoV-9p for gclcip-std-proposals@m.gmane.org; Wed, 23 Jan 2019 17:34:36 +0100 Original-Received: by mail-lj1-f198.google.com with SMTP id x18-v6sf808862lji.0 for ; 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[37.110.31.10]) by smtp.googlemail.com with ESMTPSA id x24-v6sm637195ljc.54.2019.01.23.08.34.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 23 Jan 2019 08:34:32 -0800 (PST) In-Reply-To: Content-Language: ru X-Original-Sender: andrey.semashev@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=N2nlVMnq; spf=pass (google.com: domain of andrey.semashev@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=andrey.semashev@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-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:41388 Archived-At: On 1/23/19 7:11 PM, Andrey Semashev wrote: > On 1/23/19 6:58 PM, p groarke wrote: >> I'll take a wild guess this has already been asked, thought-of or=20 >> written about, but lets ask anyways. I'm curious why one cannot write=20 >> the implementation of non-template dependent member function in a=20 >> compile unit, in the hopes of improving compile times. >> >> For example : >> >> .h >> >> | >> template >> structtest { >> intval()const; >> >> private: >> intval {42}; >> =C2=A0=C2=A0 =C2=A0 T t; >> }; >> | >> >> >> .cpp >> >> | >> // I do not depend on T, can implement in compile unit. >> // Declaration semantics unimportant. >> inttest::val()const{ >> returnval; >> } >> | >> >> >> I remember a cppcon talk from Ubisoft, where they bypass this issue by= =20 >> inheriting a base class with non-template dependent behavior=20 >> implemented in their compile unit. Template dependent behavior is=20 >> implemented in the header of the derived class. >> Why not offer this compilation behavior out-of-the-box? >=20 > I assume, the main reason is that because the method is not instantiated= =20 > until it is ODR-used (e.g. called). This is a useful property, which, in= =20 > fact, may improve compile times if the method body causes a lot of other= =20 > template instantiations or expensive code generation. Also, even if val's body does not depend on template parameters of its=20 class, it is still dependent. test::val are distinct functions for=20 different Ts. There are also template specializations to consider. --=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/f6ad2ae2-079e-3ecd-b40c-3898319a80c4%40gmail.com= .. .