220 33530 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 13:33:25 +0200 Lines: 144 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="------------456D88599976B7BA492A1A36" X-Trace: blaine.gmane.org 1501673612 24513 195.159.176.226 (2 Aug 2017 11:33:32 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 2 Aug 2017 11:33:32 +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, Thiago Macieira Original-X-From: std-proposals+bncBDH67CONY4PBBCXRQ3GAKGQEOBPH56Y@isocpp.org Wed Aug 02 13:33:28 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f69.google.com ([209.85.215.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dcru2-0005yW-0W for gclcip-std-proposals@m.gmane.org; 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[80.12.242.131]) by mx.google.com with ESMTPS id b7si3116078wma.65.2017.08.02.04.33.29 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 02 Aug 2017 04:33:29 -0700 (PDT) Received-SPF: neutral (google.com: 80.12.242.131 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.131; Original-Received: from imac-de-vicente-botet-escriba.home ([86.229.176.71]) by mwinf5d84 with ME id sBZT1v00N1YoQGN03BZTM7; Wed, 02 Aug 2017 13:33:29 +0200 X-ME-Helo: imac-de-vicente-botet-escriba.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Wed, 02 Aug 2017 13:33:29 +0200 X-ME-IP: 86.229.176.71 In-Reply-To: <2570492.NpxuI0RVu0@tjmaciei-mobl1> Content-Language: en-US X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.131 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:33530 Archived-At: This is a multi-part message in MIME format. --------------456D88599976B7BA492A1A36 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable 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 it= s >> 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=20 libraries that wrap other types to build opaque types. I've as well used underlying_cast to static_cast the underlying value to=20 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. 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/aa4104f9-5a29-c1d9-22ac-1dfa9cad8d18%40wanadoo.f= r. --------------456D88599976B7BA492A1A36 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Le 30/07/2017 =C3=A0 18:20, Thiago Macie= ira a =C3=A9crit=C2=A0:
On Sunday, 30 July 2017 04:50:41 PDT james.a.coope=
r@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 wrong name because thi=
s=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&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.


Vicente

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