220 39124 article Path: news.gmane.org!.POSTED!not-for-mail From: mihailnajdenov@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Concept-defined placeholder type Date: Thu, 12 Jul 2018 14:06:06 -0700 (PDT) Lines: 170 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_47366_1240650065.1531429566475" X-Trace: blaine.gmane.org 1531429442 14975 195.159.176.226 (12 Jul 2018 21:04:02 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 12 Jul 2018 21:04:02 +0000 (UTC) Cc: mihailnajdenov@gmail.com, zy@miator.net To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCUJ3A7GRAPRBP4FT7NAKGQEM644RQQ@isocpp.org Thu Jul 12 23:03:57 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f198.google.com ([209.85.161.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fdikn-0003mT-CV for gclcip-std-proposals@m.gmane.org; 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Thu, 12 Jul 2018 14:06:08 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a0d:eb05:: with SMTP id u5-v6ls31301ywe.35.gmail; Thu, 12 Jul 2018 14:06:07 -0700 (PDT) X-Received: by 2002:a81:78c6:: with SMTP id t189-v6mr375694ywc.7.1531429566987; Thu, 12 Jul 2018 14:06:06 -0700 (PDT) In-Reply-To: X-Original-Sender: MihailNajdenov@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:39124 Archived-At: ------=_Part_47366_1240650065.1531429566475 Content-Type: multipart/alternative; boundary="----=_Part_47367_1716113250.1531429566476" ------=_Part_47367_1716113250.1531429566476 Content-Type: text/plain; charset="UTF-8" On Thursday, July 12, 2018 at 11:20:24 PM UTC+3, Zhihao Yuan wrote: > > From: mihailn...@gmail.com > > Sent: Thursday, July 12, 2018 4:58 AM > > With types > > > > template<. . .> > > auto func() > > { > > Concept Type; > > > > if constexpr(something) > > Type var = . . .; > > else > > Type var = . . .; > > > > // use Type; > > } > > > > But this works even if Concept Type is introduced in scope (other means > included)! > > if constexpr - will physically remove the scopes altogether. And if it > is not a constexpr if, then we could init it outside of scope by other > means > > > It doesn't, "var" cannot be looked up at the "// use Type" > location, so you cannot even use decltype(var) there. > So, the scope remains? Makes sense actually. Well, we have a use case I guess :) > > > namespace n { > > > > StandardLayoutType T; //< allowed? > > > > template > > void uploadToGPU(Producer& producer) > > { > > T item = producer.next(); > > } > > That's the kind of bug that I'm looking for... > It shouldn't be allowed. > Any reason why? Except confusion and probably impl difficulties. > > -- > Zhihao Yuan, ID lichray > The best way to predict the future is to invent it. > _______________________________________________ > > > > -- 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 email 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/c9064c15-1ebb-4f2f-a32c-bedef354e29d%40isocpp.org. ------=_Part_47367_1716113250.1531429566476 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Thursday, July 12, 2018 at 11:20:24 PM UTC+3, Z= hihao Yuan wrote:
From: mihailn...@g= mail.com <mihailn...@gmail.com>=20
Sent: Thursday, July 12, 2018 4:58 AM
> With types
>=20
> template<. . .>
> auto func()
> {=20
> =C2=A0 Concept Type;
>=20
> =C2=A0 if constexpr(something)
> =C2=A0 =C2=A0 Type var =3D . . .;
> =C2=A0 else
> =C2=A0 =C2=A0 Type var =3D . . .;
>=20
> =C2=A0 // use Type;
> }
>=20
> But this works even if Concept Type is introduced in scope (other = means included)!=20
> if constexpr - will physically remove the scopes altogether. And i= f it is not a constexpr if, then we could init it outside of scope by other= means

=C2=A0
It doesn't, "var" cannot be looked up at the "// u= se Type"
location, so you cannot even use decltype(var) there.

So, the scope remains? Makes sense act= ually. Well, we have a use case I guess :)=C2=A0
=C2=A0

> namespace n {
>=20
> StandardLayoutType T; //< allowed?
>=20
> template <typename Producer>
> void uploadToGPU(Producer& producer)
> {
> =C2=A0 T item =3D producer.next();
> }

That's the kind of bug that I'm looking for...
It shouldn't be allowed.

Any reason why? Except confusion and p= robably impl difficulties.
=C2=A0
=C2=A0

--
Zhihao Yuan, ID lichray
The best way to predict the future is to invent it.
_______________________________________________
=C2=A0


--
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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/c9064c15-1ebb-4f2f-a32c-bedef354e29d= %40isocpp.org.
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