220 33538 article Path: news.gmane.org!.POSTED!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Proposal: underlying_cast Date: Wed, 2 Aug 2017 19:54:08 +0200 Lines: 195 Approved: news@gmane.org Message-ID: References: <6a2c32ed-99b5-4cc5-86a5-ee3cc07567a3@isocpp.org> <2570492.NpxuI0RVu0@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------131504E697C54933521C39FB" X-Trace: blaine.gmane.org 1501696455 4866 195.159.176.226 (2 Aug 2017 17:54:15 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 2 Aug 2017 17:54:15 +0000 (UTC) User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 To: std-proposals@isocpp.org, John McFarlane , Thiago Macieira Original-X-From: std-proposals+bncBDH67CONY4PBBQ5DRDGAKGQEKWGC5CY@isocpp.org Wed Aug 02 19:54:10 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f71.google.com ([209.85.215.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dcxqQ-0000oS-AZ for gclcip-std-proposals@m.gmane.org; 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[80.12.242.132]) by mx.google.com with ESMTPS id 79si3635719wms.259.2017.08.02.10.54.10 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 02 Aug 2017 10:54:10 -0700 (PDT) Received-SPF: neutral (google.com: 80.12.242.132 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.132; Original-Received: from imac-de-vicente-botet-escriba.home ([86.229.176.71]) by mwinf5d20 with ME id sHu81v0091YoQGN03Hu9CB; Wed, 02 Aug 2017 19:54:10 +0200 X-ME-Helo: imac-de-vicente-botet-escriba.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Wed, 02 Aug 2017 19:54:10 +0200 X-ME-IP: 86.229.176.71 In-Reply-To: Content-Language: en-US X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.132 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mailfrom=vicente.botet@wanadoo.fr 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:33538 Archived-At: This is a multi-part message in MIME format. --------------131504E697C54933521C39FB Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable Le 02/08/2017 =C3=A0 17:21, John McFarlane a =C3=A9crit : > On Wed, Aug 2, 2017 at 4:33 AM Vicente J. Botet Escriba=20 > > wrote: > > Le 30/07/2017 =C3=A0 18:20, Thiago Macieira a =C3=A9crit : >> On Sunday, 30 July 2017 04:50:41 PDTjames.a.cooper@gmail.com wrote: >>> C++ allows enums to have an underlying type specified. When seriali= sing >>> enum values it's important to use the correct type. >>> This proposal is to add a utility function that casts an enum type = to its >>> underlying value. This would make it easier to handle >>> enum types in function overloads for serialisation. For example: >>> >>> template >>> std::ostream& write(std::ostream& os, const T& v) >>> { >>> os << std::underlying_cast(v); >>> return os; >>> } >> Yes on the convenience, but "underlying_cast" is the wrong name beca= use this >> does not look like a regular cast. >> >> Something like "std::underlying_value" might be better. >> > I've used underlying(v) to get the underlying value in some of my > libraries that wrap other types to build opaque types. > > I've as well used underlying_cast to static_cast the underlying > value to another type that works with static cast > > template > U underlying_cast(T const& v) > { > return static_cast(underlying(v)); > } > > > This would be part of a library proposal for strong/opaque types. > > Question: If wrapped types are being considered, would anyone consider=20 > `chrono::duration::rep` to be the underlying type of=20 > `chrono::duration` or it is something else? Because if the former,=20 > then `to_rep` from P0675 serves a similar purpose. For me chrono::duration::rep is the underlying type an underlying type=20 is something that works not only for numeric types. Your to_rep()(v)=20 function object is similar as underlying_cast(v). Just wondering why=20 do you need a function object. Vicente --=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/db80d22b-15d6-0995-fa22-3e99eb745269%40wanadoo.f= r. --------------131504E697C54933521C39FB Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Le 02/08/2017 =C3=A0 17:21, John McFarla= ne a =C3=A9crit=C2=A0:
On Wed, Aug 2, 2017 at 4:33 AM Vicente J. Botet Escriba <vicente.botet@wanadoo.fr> wrote:
Le 30/07/2017 =C3=A0 18:20, Thiago Macieira a =C3=A9crit=C2=A0= :
On Sunday, 30 July 2017 04:50:41 PDT james.a.cooper@gmail.com=
 wrote:

C++ allows enums to have an underlying type specifie=
d. When serialising
enum values it's important to use the correct type.
This proposal is to add a utility function that casts an enum type to its
underlying value. This would make it easier to handle
enum types in function overloads for serialisation. For example:

template <typename T>
std::ostream& write(std::ostream& os, const T& v)
{
    os << std::underlying_cast(v);
    return os;
}

Yes on the convenience, but "underlying_cast" is the w=
rong name because this=20
does not look like a regular cast.

Something like "std::underlying_value" might be better.

I've used underlying(v) to get the underlying value in some of my libraries that wrap other types to build opaque types.

I've as well used underlying_cast to static_cast the underlying value to another type that works with static cast

=C2=A0=C2=A0=C2=A0 template <class U,= class T>
=C2=A0=C2=A0=C2=A0 U underlying_cast(T const& v)
=C2=A0=C2=A0=C2=A0 {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return static_cast<U>= ;(underlying(v));
=C2=A0=C2=A0=C2=A0 }


This would be part of a library proposal for strong/opaque types.

Question: If wrapped types are being considered, would anyone consider `chrono::duration::rep` to be the underlying type of `chrono::duration` or it is something else?=C2=A0 Because if th= e former, then `to_rep` from P0675 serves a similar purpose.
For me chrono::duration::rep is the underlying type an underlying type is something that works not only for numeric types. Your to_rep<T>()(v) function object is similar as underlying_cast<T= >(v). Just wondering why do you need a function object.



Vicente

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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/db80d22b-15d6-0995-fa22-3e99eb745269= %40wanadoo.fr.
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