220 18906 article Path: news.gmane.org!not-for-mail From: Igor Baidiuk Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Unified coercion protocol: static_cast explicit overload Date: Wed, 1 Jul 2015 09:38:37 -0700 (PDT) Lines: 336 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/mixed; boundary="----=_Part_2272_998513374.1435768717283" X-Trace: ger.gmane.org 1435768739 30984 80.91.229.3 (1 Jul 2015 16:38:59 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 1 Jul 2015 16:38:59 +0000 (UTC) Cc: dibeas@ieee.org To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDK4F76SSIIBBDVP2CWAKGQEYFBEIXA@isocpp.org Wed Jul 01 18:38:47 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qg0-f71.google.com ([209.85.192.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZAL25-0007dj-4g for gclcip-std-proposals@m.gmane.org; Wed, 01 Jul 2015 18:38:45 +0200 Original-Received: by qgeg89 with SMTP id g89sf56537279qge.0 for ; Wed, 01 Jul 2015 09:38:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:content-type: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=8Ftnqge6CXwNkohOoyrsW3a+vxGrmq+cqTkBqKwgTxU=; b=T4nWg8JNSYj0bAhrHA7+eAQv4MvgoUo7H1UA3iLvb0qy9mWgA9xUD78SKjrTYSvarr rblQ4n+hfDCmgoxVD2/OhPr9I0zIYZEj75NFk1tbVGkpcP72o5Zx1SlDyOEBpTmsZeB1 c9FXS4/oX5LAz0E3x9i2B1A5ejTNZJ/AkxiqeELHRnY1mA2qpw2+dIPqgz+STvbBcOSD o61pEs3dzG25SB9pEDIp46ExpxHPBSCC7/DSGHAGfbNBljUaN4VDJAYvR2edWEY693Mo NqK7ZQywFz7AV1+mOaBJnVDx6hA8lrZK/TRRfsUTnx91LYn5qyNNdf/yKeUKQiTAaa36 pyZA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:content-type: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=8Ftnqge6CXwNkohOoyrsW3a+vxGrmq+cqTkBqKwgTxU=; b=cHHPmJhRqeP6oWb27+sdbgFZ3CrAk/keZ2xhh+CcuBEHqMThKhXltO1JC6o9iqLYtw MIyA3ycE4wDZWeOtQn81AkAeFVLeiZ7Zs7oJ6lO846GfhgLqaZOWg3x04t9DnlildKb/ Wk9egeL49oP5o7UFZkEnRKmlWZwdOEB/S/w0CFNGFexHbaAE+lOlY3F+n+DhQgAw6tnv NskbwNUBBir+B3mWn+JCTS8mIfNAf3M78meurjkVQzIf7fldUV+YLzwihUfthAt5aR3A rRyrhjNxjsHS5IM3kNXvA4JfTBsT0z6QePeojEt1Ka01bK+0kq14S52QkAj99L2hhiD4 qOIA== X-Gm-Message-State: ALoCoQlv0A7z7MslEeldXsaHAIjH8CXUPDGYMF33+a+3TFBpuGQknn3fkm5PCdD+Rsuh8zrWZova X-Received: by 10.129.102.10 with SMTP id a10mr34608369ywc.28.1435768719157; Wed, 01 Jul 2015 09:38:39 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.99.10 with SMTP id p10ls892763qge.51.gmail; Wed, 01 Jul 2015 09:38:37 -0700 (PDT) X-Received: by 10.140.21.197 with SMTP id 63mr345314qgl.31.1435768717784; Wed, 01 Jul 2015 09:38:37 -0700 (PDT) In-Reply-To: X-Original-Sender: target.san@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:18906 Archived-At: ------=_Part_2272_998513374.1435768717283 Content-Type: multipart/alternative; boundary="----=_Part_2273_1577059160.1435768717283" ------=_Part_2273_1577059160.1435768717283 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable To1 convert(From const& from); To2 convert(From const& from); Any ideas? Yes, I can do template To convert(From&& from); ///... template<> To1 convert(From1 const& from); Though it's a bit ugly, and looks like reinventing the wheel for each=20 specific case. On Wednesday, July 1, 2015 at 6:53:31 PM UTC+3, David Rodr=C3=ADguez Ibeas = wrote: > > 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 =3D 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=20 >>> example, what effect do you want to acheive that is not acheived by=20 >>> 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= =20 >> want to pollute struct interface, because those conversions are used onl= y=20 >> inside of some module. >> =20 >> >>> #include >>> struct Three >>> { >>> explicit operator int() const { return 3; } >>> explicit operator std::string() const { return "three"; } >>> }; >>> >>> int main() >>> { >>> Three three; >>> auto i =3D static_cast(three); // yields 3 >>> auto s =3D static_cast(three); // yields=20 >>> std::string("three") >>> // int j =3D three; // illegal >>> // string str =3D 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 =3D 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= =20 >>>> etc. >>>> Or, allow declaring non-member conversion operators, which are explici= t=20 >>>> by default? >>>> >>>> --=20 >>>> >>>> ---=20 >>>> You received this message because you are subscribed to the Google=20 >>>> Groups "ISO C++ Standard - Future Proposals" group. >>>> To unsubscribe from this group and stop receiving emails from it, send= =20 >>>> an email to std-proposal...@isocpp.org. >>>> To post to this group, send email to std-pr...@isocpp.org. >>>> Visit this group at=20 >>>> http://groups.google.com/a/isocpp.org/group/std-proposals/. >>>> >>> >>> --=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 . >> Visit this group at=20 >> http://groups.google.com/a/isocpp.org/group/std-proposals/. >> > > --=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. ------=_Part_2273_1577059160.1435768717283 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
To1 c= onvert(From const& from);
To2 convert(From const& from);

Any ideas?

Yes,= I can do
template<typen= ame To, typename From>
To c= onvert(From&& from);

///...

template<>
To1 convert<To1, From1>(From1 const& from);
=

Though it's a bit ugly, and looks like reinve= nting the wheel for each specific case.

On Wednesday, July 1, 2015 a= t 6:53:31 PM UTC+3, David Rodr=C3=ADguez Ibeas wrote:
You could create a free function in= the module that does the same, right?

To convert(From f) { return T= o{ f.a, f.b }; }
...
auto to =3D convert(getSomeFrom());
On Wed, Jul 1, 2015 at 2:55 PM, Igor Baidiuk <= span dir=3D"ltr"><= targe...@gmail.com> 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? F= or example, what effect do you want to acheive that is not acheived by some= thing like the following?

I can= not define conversions as free-standing functions.
Sometimes it's really= useful when you want those conversions, but don't want to pollute struct i= nterface, because those conversions are used only inside of some module. 
#include <string>
struct Three
{
   = ; explicit operator int() const { return 3; }
    explici= t operator std::string() const { return "three"; }
};

int main()<= br>{
    Three three;
    auto i =3D st= atic_cast<int>(three); // yields 3
    auto s =3D s= tatic_cast<std::string>(three); // yields std::string("three")    // int j =3D three; // illegal
    /= / string str =3D three; // illegal
}

Cheers!

2015-07-= 01 7:17 GMT-04:00 Igor Baidiuk <ta= rge...@gmail.com>:
<= span>
What if we could define
op= erator = static_cast<To>(From const& from)
{
    return { from.a, from.b};=
}
// la= ter in code
From from;
auto to =3D static_cast<To>(from);
as means of non-member, explicit conversion syntax?
So we don't need t= o write tons of functions like toFoo, toBar, toBaz etc.
Or, allow declar= ing non-member conversion operators, which are explicit by default?

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