220 41396 <9c7f6fed-17c2-cd06-1b86-b2a64d12437e@gmail.com> article Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Improving compile times for non-template dependent member functions. 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[66.194.253.20]) by smtp.googlemail.com with ESMTPSA id o22sm35536401qkk.93.2019.01.24.12.00.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 24 Jan 2019 12:00:45 -0800 (PST) Openpgp: preference=signencrypt In-Reply-To: <511c9222-ae06-222e-4f1b-c4843b5f83fe@gmail.com> Content-Language: en-US X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b="CY//QryN"; spf=pass (google.com: domain of mwoehlke.floss@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=mwoehlke.floss@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:41396 Archived-At: On 23/01/2019 11.30, Andrey Semashev wrote: > On 1/23/19 7:20 PM, Thiago Macieira wrote: >> On Wednesday, 23 January 2019 07:58:54 PST p groarke wrote: >>> template >>> struct test { >>> =C2=A0=C2=A0=C2=A0=C2=A0 int val() const; >>> >>> private: >>> =C2=A0=C2=A0=C2=A0=C2=A0 int val_ { 42 }; >>> =C2=A0=C2=A0=C2=A0=C2=A0 T t; >>> }; >> >> Explain how, given the above, the compiler can decide whether test::val(= ) >> depends on T or not. >> >> Remember: this is all the compiler sees when compiling other >> translation units >> that include this header. >=20 > It doesn't need to know that. When val() is ODR-used, the compiler will > simply leave a reference to the val symbol to be resolved by the linker. Er... that works today (since C++98 even). It requires explicit template instantiation, though. You would need a way to tell the compiler a) to assume that val() will not be dependent, and b) that a definition is non-dependent. > The question is really whether the compiler that sees the implementation > of val() should emit its compiled body. Currently it doesn't, presumably > due to the reason I described in my reply. The point (b) above would take care of this. It might look something like: // .h template struct test { int val() const =3D template<...>; //... }; // .cpp template <> test<...>::val() const // non-dependent specialization { ... } The `=3D template<...>` tells the compiler that, if it hasn't seen otherwise (e.g. a specialization), calls to test::val should be replaced with calls to the non-type-dependent symbol test<...>::val (which is also declared by the same syntax). The latter syntax for defining said symbol will of course always generate code. Note, additionally, that the template parameter is unavailable in the definition of this member, so anything that would depend on it (including class statics, I suppose) is an error. (Straw syntax, of course...) --=20 Matthew --=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. 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