220 18905 article Path: news.gmane.org!not-for-mail From: =?UTF-8?Q?David_Rodr=C3=ADguez_Ibeas?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Unified coercion protocol: static_cast explicit overload Date: Wed, 1 Jul 2015 16:53:29 +0100 Lines: 214 Approved: news@gmane.org Message-ID: References: <5c654bc3-5294-4f8a-bf1a-bf4a9f6c8603@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a11c35152f7bed10519d2525b X-Trace: ger.gmane.org 1435766012 16631 80.91.229.3 (1 Jul 2015 15:53:32 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 1 Jul 2015 15:53:32 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBDIIVO6GQULBB6UZ2CWAKGQEWCLJPCQ@isocpp.org Wed Jul 01 17:53:31 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-la0-f69.google.com ([209.85.215.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZAKKJ-0001H6-CA for gclcip-std-proposals@m.gmane.org; Wed, 01 Jul 2015 17:53:31 +0200 Original-Received: by lagx9 with SMTP id x9sf13310948lag.2 for ; Wed, 01 Jul 2015 08:53:30 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:sender:in-reply-to:references:date :message-id:subject:from:to:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=EA3ipwihJNkDgm8SoiaWJNnWmP4Q1ru1/6bXAG/FtIE=; b=knJpqV4hpzV2nENM/NjBT4PbwB1V9G437ukNwNUiBlfpDo1uyJKMZyIhE/TityunLX 4hQfA8D5Zl099RM9IJb2UIpNQi+Il/L8hHf6fdDePy7Ao54BzQQn5UMBP1IerqUJYZ0i vckPFRGWjSPRBFMa/bwMgSlW1X3uiuscXC0PAvcmorm/SLZEgpiAMvoPEvv8gHJJmNgs F9WlQVd7EF48nlNHr27m/dP6sIJETSnf+w4zqJDjlXrAWZrV4ymFAMsnAV5hL4S/jXQb 5CT78YuKIflyXzdjq67c6E0poN0ZTTRuCGFCxR4NnO8EDlYCYh6TvFY8MQ8NK+ZKaHVR P9Zg== X-Gm-Message-State: ALoCoQmSzHXRe1Dg37vKAT8ZzUgCE8adRtQx8nmssdSlX8xm3+irEd6oZ91ljXl7DfCvkFPzoc0X X-Received: by 10.112.28.111 with SMTP id a15mr17463094lbh.21.1435766010898; Wed, 01 Jul 2015 08:53:30 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.204.168 with SMTP id kz8ls185806lac.105.gmail; Wed, 01 Jul 2015 08:53:29 -0700 (PDT) X-Received: by 10.112.72.132 with SMTP id d4mr25951543lbv.1.1435766009696; Wed, 01 Jul 2015 08:53:29 -0700 (PDT) Original-Received: from mail-lb0-x22c.google.com (mail-lb0-x22c.google.com. [2a00:1450:4010:c04::22c]) by mx.google.com with ESMTPS id q10si2042482lbp.109.2015.07.01.08.53.29 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 Jul 2015 08:53:29 -0700 (PDT) Received-SPF: pass (google.com: domain of dribeas@gmail.com designates 2a00:1450:4010:c04::22c as permitted sender) client-ip=2a00:1450:4010:c04::22c; Original-Received: by lbnk3 with SMTP id k3so15662954lbn.1 for ; Wed, 01 Jul 2015 08:53:29 -0700 (PDT) X-Received: by 10.152.43.110 with SMTP id v14mr25985976lal.4.1435766009345; Wed, 01 Jul 2015 08:53:29 -0700 (PDT) Original-Sender: dribeas@gmail.com Original-Received: by 10.152.43.170 with HTTP; Wed, 1 Jul 2015 08:53:29 -0700 (PDT) In-Reply-To: X-Original-Sender: dibeas@ieee.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of dribeas@gmail.com designates 2a00:1450:4010:c04::22c as permitted sender) smtp.mail=dribeas@gmail.com; dkim=pass header.i=@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:18905 Archived-At: --001a11c35152f7bed10519d2525b Content-Type: text/plain; charset=UTF-8 You could create a free function in the module that does the same, right? To convert(From f) { return To{ f.a, f.b }; } .... auto to = convert(getSomeFrom()); On Wed, Jul 1, 2015 at 2:55 PM, Igor Baidiuk wrote: > > > On Wednesday, July 1, 2015 at 4:17:23 PM UTC+3, Patrice Roy wrote: >> >> What is missing from explicit conversion operators in your mind? For >> example, what effect do you want to acheive that is not acheived by >> something like the following? >> >> I cannot define conversions as free-standing functions. > Sometimes it's really useful when you want those conversions, but don't > want to pollute struct interface, because those conversions are used only > inside of some module. > > >> #include >> struct Three >> { >> explicit operator int() const { return 3; } >> explicit operator std::string() const { return "three"; } >> }; >> >> int main() >> { >> Three three; >> auto i = static_cast(three); // yields 3 >> auto s = static_cast(three); // yields >> std::string("three") >> // int j = three; // illegal >> // string str = three; // illegal >> } >> >> Cheers! >> >> 2015-07-01 7:17 GMT-04:00 Igor Baidiuk : >> >>> What if we could define >>> operator static_cast(From const& from) >>> { >>> return { from.a, from.b}; >>> } >>> // later in code >>> From from; >>> auto to = static_cast(from); >>> as means of non-member, explicit conversion syntax? >>> So we don't need to write tons of functions like toFoo, toBar, toBaz etc. >>> Or, allow declaring non-member conversion operators, which are explicit >>> by default? >>> >>> -- >>> >>> --- >>> 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-proposal...@isocpp.org. >>> To post to this group, send email to std-pr...@isocpp.org. >>> Visit this group at >>> http://groups.google.com/a/isocpp.org/group/std-proposals/. >>> >> >> -- > > --- > 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. > Visit this group at > http://groups.google.com/a/isocpp.org/group/std-proposals/. > -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. --001a11c35152f7bed10519d2525b Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
You could create a free function in the module that does t= he same, right?

To convert(From f) { return To{ f.a, f.b }; }
...=
auto to =3D convert(getSomeFrom());
On Wed, Jul 1, 2015 at 2:55 PM, Igor Baidiuk <target.san@gmail.com> wrote:


On Wednesday, July 1, 2015 a= t 4:17:23 PM UTC+3, Patrice Roy wrote:
What is missing from explicit conversion operators= in your mind? For example, what effect do you want to acheive that is not = acheived by something like the following?

<= /span>
I cannot define conversions as free-standing functions.
Somet= imes it's really useful when you want those conversions, but don't = want to pollute struct interface, because those conversions are used only i= nside of some module.
=C2=A0
#include <string>
str= uct Three
{
=C2=A0=C2=A0=C2=A0 explicit operator int() const { return= 3; }
=C2=A0=C2=A0=C2=A0 explicit operator std::string() const { return = "three"; }
};

int main()
{
=C2=A0=C2=A0=C2=A0 Thr= ee three;
=C2=A0=C2=A0=C2=A0 auto i =3D static_cast<int>(three); /= / yields 3
=C2=A0=C2=A0=C2=A0 auto s =3D static_cast<std::string>(= three); // yields std::string("three")
=C2=A0=C2=A0=C2=A0 // i= nt j =3D three; // illegal
=C2=A0=C2=A0=C2=A0 // string str =3D three; /= / illegal
}

Cheers!
=

2015-07-01 7:17 GMT-04= :00 Igor Baidiuk <targe...@gmail.c= om>:
What if we could define
opera= tor sta= tic_cast<To>(From const& from)
{
=C2=A0 =C2=A0 return { from.a, from.b};<= /span>
}
// lat= er in code
From from;
auto to =3D static_cast<To>(from);
as means of non-member, explicit conversion syntax?
So we don't nee= d to write tons of functions like toFoo, toBar, toBaz etc.
Or, allow dec= laring non-member conversion operators, which are explicit by default?

--

---
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 To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposal...@isocpp.org.
To post to this group, send email to std-pr...@isocpp.o= rg.
Visit this group at http://groups.google.com= /a/isocpp.org/group/std-proposals/.

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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.
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