220 26327 article Path: news.gmane.org!not-for-mail From: Sergey Vidyuk Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: statement folding on variadic templates parameters pack Date: Mon, 13 Jun 2016 12:00:52 -0700 (PDT) Lines: 161 Approved: news@gmane.org Message-ID: References: <1e3daa7c-e10a-4589-8118-26f47bc1a0df@isocpp.org> <2d8458f8-27b2-464f-a16e-fc866ccfd2cd@isocpp.org> <8dc1e665-42a3-4ef0-a2d2-3773afab170c@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_582_2101369963.1465844452217" X-Trace: ger.gmane.org 1465844457 19963 80.91.229.3 (13 Jun 2016 19:00:57 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 13 Jun 2016 19:00:57 +0000 (UTC) Cc: inkwizytoryankes@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCB6HO5JRMARBZMF7S5AKGQE2S5QQVA@isocpp.org Mon Jun 13 21:00:56 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f70.google.com ([209.85.214.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bCX6V-0006t5-9h for gclcip-std-proposals@m.gmane.org; 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Mon, 13 Jun 2016 12:00:54 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.50.146 with SMTP id j140ls975658ita.21.gmail; Mon, 13 Jun 2016 12:00:53 -0700 (PDT) X-Received: by 10.36.103.134 with SMTP id u128mr295425itc.5.1465844453326; Mon, 13 Jun 2016 12:00:53 -0700 (PDT) In-Reply-To: <8dc1e665-42a3-4ef0-a2d2-3773afab170c@isocpp.org> X-Original-Sender: sir.vestnik@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:26327 Archived-At: ------=_Part_582_2101369963.1465844452217 Content-Type: multipart/alternative; boundary="----=_Part_583_567470926.1465844452218" ------=_Part_583_567470926.1465844452218 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable =D0=B2=D0=BE=D1=81=D0=BA=D1=80=D0=B5=D1=81=D0=B5=D0=BD=D1=8C=D0=B5, 12 =D0= =B8=D1=8E=D0=BD=D1=8F 2016 =D0=B3., 17:13:48 UTC+6 =D0=BF=D0=BE=D0=BB=D1=8C= =D0=B7=D0=BE=D0=B2=D0=B0=D1=82=D0=B5=D0=BB=D1=8C=20 inkwizyt...@gmail.com =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB: > > I was referring to switch after applying `for constexpr`. Some thing like= =20 > that: > switch (x) > { > for constexpr (typename T : Op...) > { > case T::OpId: T::OpFunc(); break; > } > break; > } > //After `for constexpr` "unroll" > switch (x) > { > case Op0::OpId: Op0::OpFunc(); break; > case Op1::OpId: Op1::OpFunc(); break; > case Op2::OpId: Op2::OpFunc(); break; > case Op3::OpId: Op3::OpFunc(); break; > } > And in second switch today compilers do that I mentioned (if `OpId` creat= e=20 > proper range). `for constexpr` is not trivial but if it support `case` th= en=20 > getting jump table from `switch` and `for constexpr` will be trivial. > > Maybe it's better to have syntax to expand parameters pack into set of case= =20 statements. Posibility to mix switch with loops is one of the most=20 confusing and dangerous part of the language. I fill it's better to avoid= =20 adding for constexpr as a common practice to unpack parameters pack into=20 cases. -- Sergey=20 =20 --=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/a7bcde4a-19e9-4916-b292-b48adf2345a4%40isocpp.or= g. ------=_Part_583_567470926.1465844452218 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
=D0=B2=D0=BE=D1=81=D0=BA=D1=80=D0=B5=D1=81=D0=B5=D0=BD=D1= =8C=D0=B5, 12 =D0=B8=D1=8E=D0=BD=D1=8F 2016 =D0=B3., 17:13:48 UTC+6 =D0=BF= =D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=D0=B2=D0=B0=D1=82=D0=B5=D0=BB=D1=8C inkwizyt= ....@gmail.com =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB:
I was referring to switch afte= r applying `for constexpr`. Some thing like that:
switch (x)
= {
=C2=A0 =C2=A0 for constexpr (typename T : Op...)
=C2=A0 =C2=A0 {
=C2=A0 =C2= =A0 case T::Op= Id: T::OpFunc<= /span>(); break;
=C2=A0 =C2=A0 }
=C2=A0 =C2=A0 break;
}
//After `for constexp= r` "unroll"
switch (x)
{
=C2=A0 =C2=A0 case Op0::OpId: Op0::OpFunc(); break;
=C2=A0 =C2=A0 case Op1::OpId= : Op1::OpFunc(); break;
=C2=A0 =C2=A0 <= /span>case Op2::OpId:= Op2::OpFunc(); break;
=C2=A0 =C2=A0 ca= se Op3<= /span>::OpId: = Op3::OpFunc();= break<= span style=3D"color:#660">;
}
And in second switch today compilers do that I mentioned (if = `OpId` create proper range). `for constexpr` is not trivial but if it suppo= rt `case` then getting jump table from `switch` and `for constexpr` will be= trivial.


Maybe it's better to= have syntax to expand parameters pack into set of case statements. Posibil= ity to mix switch with loops is one of the most confusing and dangerous par= t of the language. I fill it's better to avoid adding for constexpr as = a common practice to unpack parameters pack into cases.

-- Sergey
=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/a7bcde4a-19e9-4916-b292-b48adf2345a4= %40isocpp.org.
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