220 33535 article Path: news.gmane.org!.POSTED!not-for-mail From: John McFarlane Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Proposal: underlying_cast Date: Wed, 02 Aug 2017 15:21:42 +0000 Lines: 188 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="94eb2c0defc0dd65860555c6d24f" X-Trace: blaine.gmane.org 1501687314 8327 195.159.176.226 (2 Aug 2017 15:21:54 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 2 Aug 2017 15:21:54 +0000 (UTC) To: std-proposals@isocpp.org, Thiago Macieira Original-X-From: std-proposals+bncBDS7B7WQUYOBBEW4Q7GAKGQE4CEO64Y@isocpp.org Wed Aug 02 17:21:50 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wr0-f197.google.com ([209.85.128.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dcvT4-0001wN-0C for gclcip-std-proposals@m.gmane.org; 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[209.85.128.179]) by mx.google.com with ESMTPS id z13si10041705edj.291.2017.08.02.08.21.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 02 Aug 2017 08:21:53 -0700 (PDT) Received-SPF: pass (google.com: domain of mcfarlane.john@gmail.com designates 209.85.128.179 as permitted sender) client-ip=209.85.128.179; Original-Received: by mail-wr0-f179.google.com with SMTP id y43so20066429wrd.3 for ; Wed, 02 Aug 2017 08:21:53 -0700 (PDT) X-Received: by 10.223.146.35 with SMTP id 32mr17276886wrj.76.1501687313160; Wed, 02 Aug 2017 08:21:53 -0700 (PDT) In-Reply-To: X-Original-Sender: john@mcfarlane.name X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of mcfarlane.john@gmail.com designates 209.85.128.179 as permitted sender) smtp.mailfrom=mcfarlane.john@gmail.com 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:33535 Archived-At: --94eb2c0defc0dd65860555c6d24f Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 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 : > > On Sunday, 30 July 2017 04:50:41 PDT james.a.cooper@gmail.com wrote: > > C++ allows enums to have an underlying type specified. 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 > 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 because t= his > 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 `chrono::duration::rep` to be the underlying type of `chrono::duration` or it is something else? Because if the former, then `to_rep` from P0675 serves a similar purpose. > Vicente > > -- > 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. > To view this discussion on the web visit > https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/aa4104f9-5a2= 9-c1d9-22ac-1dfa9cad8d18%40wanadoo.fr > > . > --=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/CABPJVnSrvKQPXqRPDju8PnnXv_M6%2B3EuPCuqMkMb9QigC= -6fTQ%40mail.gmail.com. --94eb2c0defc0dd65860555c6d24f Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
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 specified. When se=
rialising
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&= #39;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_ca= st the underlying value to another type that works with static cast

=C2=A0=C2=A0=C2=A0 template <class U, class T&g= 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>(underlyi= ng(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 considere= d, would anyone consider `chrono::duration::rep` to be the underlying type = of `chrono::duration` or it is something else?=C2=A0 Because if the former,= then `to_rep` from P0675 serves a similar purpose.

Vicente
=20

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To view this discussion on the web visit = https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/aa4104f9-5a29-= c1d9-22ac-1dfa9cad8d18%40wanadoo.fr.

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