220 31472 article Path: news.gmane.org!.POSTED!not-for-mail From: Erich Keane Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: overloading by constexpr (round 2?) Date: Mon, 6 Mar 2017 15:16:53 -0800 (PST) Lines: 231 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_659_1802273394.1488842213842" X-Trace: blaine.gmane.org 1488842222 23692 195.159.176.226 (6 Mar 2017 23:17:02 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 6 Mar 2017 23:17:02 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCWZXNPJO4IONW7XYUCRUBHD3EIOW@isocpp.org Tue Mar 07 00:16:53 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f197.google.com ([209.85.161.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cl1s1-0004s3-OI for gclcip-std-proposals@m.gmane.org; Tue, 07 Mar 2017 00:16:50 +0100 Original-Received: by mail-yw0-f197.google.com with SMTP id k13sf50521163ywk.2 for ; Mon, 06 Mar 2017 15:16:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=refI9LgXwOP9YWY3qJRpC1/GIdg66+fHrbhw2xGiofo=; b=ryVagWJQm6vUN7Vi/q3wCD3n7KaVPf+NyTAJumDhwJVt6Z8XgCKJXcmPtgWMUhRTaL 9QIrzqzFbyBw3914GPh9i5692sDcuEJd6gfAHcAusaFk0LONyQ3Loi0AV4EJFEcEx3rA Grr59QOhbNEwda3KD/0SjbGFuNqeR2FyCPfWOwTLVGJUN90bTrkBKu5HoYZ5x+UJHcBL JXhPBOwzmNI8uOtvC56nBaK6ak84ahuCKc9qNCzZEWNgKjoGP50/WJLm/zv/R35Dk1YS tnyL1l3HlQbbLdFFESEP6tXe0QQNYwadLkRVRkIMc6btM/lPuRqLL9PUP0ZpAAwcMTJr EDOw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=refI9LgXwOP9YWY3qJRpC1/GIdg66+fHrbhw2xGiofo=; b=Oaclg/HD+YKrUtsW3pZ/HaRXNHwc+cL1rMwqPW4RCqFvuyIM3f1kK3cWqHtVLTyoON 5E70QpZhAuGNEXjUUxdYF/6kYVd1j+Q2oiPg/r9CfR08IhDIKSxRIbasG80QPyDKvUW1 kqrw1fiY6hZucHFKRCyVxZMUxcjmkU6VJayYJBQwrWv9scNuHrShZuKL0UDrqfWhchyU xlz3fnHisIv06eZBRryv0Wn0REZzlC7lwiPhMonUNTRarfk1QbU891tTZRgDnOaMNGsk /eISSqdbzdHv1k148PMTGiLdT0alY940j8YGrfEosJMyPbrhODshw35GLwWJQADp0hPa 0mDA== X-Gm-Message-State: AMke39nIJcZCYomCe1Xph/YI6ZWNMmr1P5iSjRiHq8zC6KjV/dJymuc5NCtoDcOeJ5jJBA== X-Received: by 10.13.238.134 with SMTP id x128mr8203430ywe.59.1488842215328; Mon, 06 Mar 2017 15:16:55 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.62.180 with SMTP id b49ls18206441otc.36.gmail; Mon, 06 Mar 2017 15:16:54 -0800 (PST) X-Received: by 10.157.82.72 with SMTP id q8mr1345161otg.4.1488842214425; Mon, 06 Mar 2017 15:16:54 -0800 (PST) In-Reply-To: X-Original-Sender: erich.keane@verizon.net 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:31472 Archived-At: ------=_Part_659_1802273394.1488842213842 Content-Type: multipart/alternative; boundary="----=_Part_660_2000997385.1488842213843" ------=_Part_660_2000997385.1488842213843 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable We also approved "do constexpr" functions which Daveed also presented=20 (constexpr ONLY functions). =20 do constexpr void f(){...} // Function can only be called at=20 compiletime, error otherwise. The idea of overloading based on constexpr'ness of a function came up in=20 the break, and a number of people mentioned there were some significant=20 issues with it, and it seemed that 'if (constexpr())' (though with a=20 different, pseudo-library function spelling) had significantly more=20 consensus. On Monday, March 6, 2017 at 1:30:33 PM UTC-8, Richard Smith wrote: > > You might want to get in touch with the author of=20 > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0595r0.html=20 > (which was discussed in Evolution last week and seems to have had a=20 > favourable reception). > > On 6 March 2017 at 10:15, dgutson . >= =20 > wrote: > >> I'm proposing the ability to provide two versions of a function,=20 >> overloaded by the constexpr specifier: one constexpr version and another= =20 >> non-constexpr version, and let the compiler use the appropriate one=20 >> according to the context. >> >> A slightly similar subject has been discussed before ( >> https://groups.google.com/a/isocpp.org/d/topic/std-proposals/oxijwTY-ft4= /discussion=20 >> ). >> Additionally, people seems to be interested in detecting constexpr-ness= =20 >> (e.g.=20 >> http://stackoverflow.com/questions/15232758/detecting-constexpr-with-sfi= nae)=20 >> to achieve the same "manually". >> >> I'm talking about to make this simpler: >> >> constexpr int f() >> { >> return 1; >> } >> >> int f() >> { >> return 2; >> } >> >> constexpr auto a =3D f(); // a =3D 1 >> auto fun =3D std::function(f); >> int b =3D fun(); // b =3D 2 >> >> If there is some interest, I can star working in a gcc fork as a=20 >> prototype. >> >> BRgds, >> >> Daniel. >> >> >> --=20 >> Who=E2=80=99s got the sweetest disposition? >> One guess, that=E2=80=99s who? >> Who=E2=80=99d never, ever start an argument? >> Who never shows a bit of temperament? >> Who's never wrong but always right? >> Who'd never dream of starting a fight? >> Who get stuck with all the bad luck?=20 >> >> --=20 >> You received this message because you are subscribed to the Google Group= s=20 >> "ISO C++ Standard - Future Proposals" group. >> To unsubscribe from this group and stop receiving emails from it, send a= n=20 >> email to std-proposal...@isocpp.org . >> To post to this group, send email to std-pr...@isocpp.org . >> To view this discussion on the web visit=20 >> https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAFdMc-2q3K= pV%2Bm5cfWr6b02XmHVUdxsNCNAVFG%2BmzCv0QY7ZRg%40mail.gmail.com=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/a0f4db51-ab03-4173-979e-52613b9577a2%40isocpp.or= g. ------=_Part_660_2000997385.1488842213843 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
We also approved "do constexpr" functions which = Daveed also presented (constexpr ONLY functions).=C2=A0

=C2=A0=C2= =A0=C2=A0 do constexpr void f(){...} // Function can only be called at comp= iletime, error otherwise.

The idea of overloading based on constexpr= 'ness of a function came up in the break, and a number of people mentio= ned there were some significant issues with it, and it seemed that 'if = (constexpr())' (though with a different, pseudo-library function spelli= ng) had significantly more consensus.

On Monday, March 6, 2017 at 1:= 30:33 PM UTC-8, Richard Smith wrote:
You might want to ge= t in touch with the author of http://www.open-std.org/jtc1/sc22/wg21/docs/pape= rs/2017/p0595r0.html (which was discussed in Evolution last week a= nd seems to have had a favourable reception).

On 6 March 2017 at 10:15, dgutson .= <daniel...@gmail.com> wrote:
I'm pr= oposing the ability to provide two versions of a function,=20 overloaded by the constexpr specifier: one constexpr version and another non-constexpr version, and let the compiler use the appropriate one=20 according to the context.

A slightly similar subjec= t has been discussed before (https://groups.google.co= m/a/isocpp.org/d/topic/std-proposals/oxijwTY-ft4/discussion<= /a> ).
I'm talking about to make this simpler:
=
constexpr int f()
{
=C2=A0=C2=A0=C2=A0 return 1;<= br>
}

int f()
{
=C2=A0=C2=A0= =C2=A0 return 2;
}

constexpr auto a =3D f()= ;=C2=A0=C2=A0=C2=A0 // a =3D 1
auto fun =3D std::function<= int(void)>(f);
int b =3D fun();=C2=A0=C2=A0 // b =3D 2
=
If there is some interest, I can star working in a gcc = fork as a prototype.

BRgds,

=C2=A0=C2= =A0=C2=A0 Daniel.


--
Who=E2=80=99s got the sw= eetest disposition?
One guess, that=E2=80=99s who?
Who=E2=80=99d neve= r, ever start an argument?
Who never shows a bit of temperament?
Who&= #39;s never wrong but always right?
Who'd never dream of starting a = fight?
Who get stuck with all the bad luck?

<= /div>

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