220 18901 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 06:55:52 -0700 (PDT) Lines: 186 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_89_176607337.1435758952320" X-Trace: ger.gmane.org 1435758961 23801 80.91.229.3 (1 Jul 2015 13:56:01 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 1 Jul 2015 13:56:01 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDK4F76SSIIBB2PCZ6WAKGQERKL2TPI@isocpp.org Wed Jul 01 15:56:01 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f200.google.com ([209.85.213.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZAIUa-0001TR-2m for gclcip-std-proposals@m.gmane.org; Wed, 01 Jul 2015 15:56:00 +0200 Original-Received: by igcsj18 with SMTP id sj18sf102956912igc.2 for ; Wed, 01 Jul 2015 06:55:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to: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=PaZhvoIhtPCJBIv1IV+LmcNvevOuXXbgzbrQaNg/hUU=; b=hSx3qjtqbzxzIxdrytek1t+ys/QekUtFoGMSKL51wnEKfcJakuHi4iz5HgCpOeUe5a +FZynsprRDTK6kWqVf3yAKMd9uOXh7x9UEa0qcDL0omOxF+oiuMG+W2U4v0bIyy6LCJa Bb9GSDNYldNLr41EWZKHknbEKkpupfHow+MqRqWzQBr9+pKwSq2j87MXrkIKnEa6XRuU n7s54JHmWh9UOeXI5OxkpH67P0pKvJgUATDnOztGx/Sc/odO5WXlDLRnW30052grPt8m V1BbHJj+ukdxf/bY2m/ZzEFe50cixEeyobiq+3opRNmXkZ8nHts0+c2INyNS4ND+1zBr bQXA== 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: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=PaZhvoIhtPCJBIv1IV+LmcNvevOuXXbgzbrQaNg/hUU=; b=Qe2aqqPHN4SXiF9+3I75k2y7RPtYNLcNgaeClvWS8vQ0+DejHnsNmFmpf6pSyoP7Dn KiXbJiy/wEzcGfafNLIomPW9CSr9oL8vDPNYgvFYOM77V+z98rUnwejJvc6vtAoHOycT 2dnPASCPeJcrr+Hq/wDOzr+sRhRR2VuLV+WkZaQteqbf+NMZ1Yxjin15ZyzsnZU0bTJo qgGxxcd7HxlnwawoDG/vHqPGkaFG6eb97F9pXOelTcWJsELiV2y1QvMPILPcsi9MRYxC pokKTE6Nx9y26qsZSvv5UYg3XE32+hxctb3opAaIm3AHUT31vqOGHDYm1ZDWDrzhJtI7 YwOw== X-Gm-Message-State: ALoCoQnuyeCRv+km1c7ScR2Ck4wVj3AYXDlaNNXlc36qy2V1i/FiOe86egdATuYW85/hKO+CGX9f X-Received: by 10.42.79.5 with SMTP id p5mr4168696ick.26.1435758954136; Wed, 01 Jul 2015 06:55:54 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.80.179 with SMTP id c48ls733360qgd.93.gmail; Wed, 01 Jul 2015 06:55:52 -0700 (PDT) X-Received: by 10.140.91.19 with SMTP id y19mr208582qgd.6.1435758952840; Wed, 01 Jul 2015 06:55:52 -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:18901 Archived-At: ------=_Part_89_176607337.1435758952320 Content-Type: multipart/alternative; boundary="----=_Part_90_417112805.1435758952320" ------=_Part_90_417112805.1435758952320 Content-Type: text/plain; charset=UTF-8 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/. ------=_Part_90_417112805.1435758952320 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Wednesday, July 1, 2015 at 4:17:23 PM UTC+3, Pa= trice Roy wrote:
What is missing from explicit conversion operators in your mind? Fo= r example, what effect do you want to acheive that is not acheived by somet= hing like the following?

I cannot defi= ne 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.
 <= br>
#include <string>
struct Three
{
    explici= t operator int() const { return 3; }
    explicit operato= r std::string() const { return "three"; }
};

int main()
{
&= nbsp;   Three three;
    auto i =3D static_cast= <int>(three); // yields 3
    auto s =3D static_cas= t<std::string>(three); // yields std::string("three")
 &= nbsp;  // int j =3D three; // illegal
    // string = str =3D three; // illegal
}

<= blockquote class=3D"gmail_quote" style=3D"margin: 0;margin-left: 0.8ex;bord= er-left: 1px #ccc solid;padding-left: 1ex;">
Che= ers!

2015-07-01 7:17 GMT-04:00= Igor Baidiuk <targe...@gmail.com>:
What if we could define
operator static_cast<To>(From const& from)
{
    return { from.a, from.b};
}
// later in code
From from;
auto to =3D static_cast<To>(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 defa= ult?

--

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