220 30180 article Path: news.gmane.org!.POSTED!not-for-mail From: m.cencora@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: enum_cast proposal Date: Tue, 3 Jan 2017 08:22:52 -0800 (PST) Lines: 188 Approved: news@gmane.org Message-ID: References: <1483532086.2yCkjVBYWJ@tjmaciei-mobl1> <2998762.etaySSRi7N@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1219_699239157.1483460572939" X-Trace: blaine.gmane.org 1483460580 29072 195.159.176.226 (3 Jan 2017 16:23:00 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 3 Jan 2017 16:23:00 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBD7YFUMJRYMBBXM7V7BQKGQESL6B6DA@isocpp.org Tue Jan 03 17:22:50 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f69.google.com ([209.85.213.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cORrO-0006Om-0T for gclcip-std-proposals@m.gmane.org; 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Tue, 03 Jan 2017 08:22:54 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.23.193 with SMTP id j59ls41817062otj.24.gmail; Tue, 03 Jan 2017 08:22:53 -0800 (PST) X-Received: by 10.157.17.3 with SMTP id g3mr2883516ote.8.1483460573373; Tue, 03 Jan 2017 08:22:53 -0800 (PST) In-Reply-To: <2998762.etaySSRi7N@tjmaciei-mobl1> X-Original-Sender: m.cencora@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:30180 Archived-At: ------=_Part_1219_699239157.1483460572939 Content-Type: multipart/alternative; boundary="----=_Part_1220_5047470.1483460572939" ------=_Part_1220_5047470.1483460572939 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable W dniu wtorek, 3 stycznia 2017 16:56:35 UTC+1 u=C5=BCytkownik Thiago Maciei= ra=20 napisa=C5=82: > > On ter=C3=A7a-feira, 3 de janeiro de 2017 07:06:10 BRST m.ce...@gmail.com= =20 > wrote:=20 > > Compiler should synthesize a function like below:=20 > >=20 > > optional enum_cast(int x)=20 > > {=20 > > switch(x)=20 > > {=20 > > case red:=20 > > case green:=20 > > case blue:=20 > > return static_cast(x);=20 > > default:=20 > > return nullopt;=20 > > }=20 > > }=20 > > How do you know whether a use of enum_cast is compile-time or whether it= =20 > is=20 > runtime?=20 > > I don't know and I don't care. The function should be constexpr to support= =20 both cases.=20 =20 > static_cast is always compile time and always succeeds or produces a=20 > compilation error. Therefore, checking at runtime is unnecessary.=20 > > dynamic_cast is almost always runtime and its result needs to be checked= =20 > at=20 > runtime.=20 > > Also, where did that optional come from? If it's going to use optional,= =20 > then=20 > it needs to be a library feature.=20 > Just a first idea on dealing with failure cases. Not really important at=20 this point. What I'd like to hear now is whether anyone else would find such a=20 functionality useful? Do you consider it a good idea to put it into C++ standard/library? =20 > > > Of course it could implement it more efficently (as range check instead= =20 > of=20 > > switch if all enumerators are consecutive integers).=20 > > One would expect the compilers to be smart enough to do that with a switc= h=20 > block that is contiguous. Still, QoI issue.=20 > > --=20 > Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org=20 > Software Architect - Intel Open Source Technology Center=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/d4b84145-05e8-452f-ba08-dae9bbe34e04%40isocpp.or= g. ------=_Part_1220_5047470.1483460572939 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
W dniu wtorek, 3 stycznia 2017 16:56:35 UTC+1 u=C5=BCytkow= nik Thiago Macieira napisa=C5=82:
On ter=C3=A7a-feira, 3 de janeiro de 2017 07:06:10 BRST m.ce...@gmail.com= wrote:
> Compiler should synthesize a function like below:
>=20
> optional<color> enum_cast(int x)
> {
> =C2=A0 =C2=A0 switch(x)
> =C2=A0 =C2=A0 {
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 case red:
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 case green:
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 case blue:
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return static_cast<co= lor>(x);
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 default:
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return nullopt;
> =C2=A0 =C2=A0 }
> }

How do you know whether a use of enum_cast is compile-time or whether i= t is=20
runtime?


I don't know and I don't care.= The function should be constexpr to support both cases.=C2=A0
= =C2=A0
static_cast is alw= ays compile time and always succeeds or produces a=20
compilation error. Therefore, checking at runtime is unnecessary.

dynamic_cast is almost always runtime and its result needs to be checke= d at=20
runtime.

Also, where did that optional come from? If it's going to use optio= nal, then=20
it needs to be a library feature.

Just a first idea on dealing with fail= ure cases. Not really important at this point.

Wha= t I'd like to hear now is whether anyone else would find such a functio= nality useful?
Do you consider it a good idea to put it into C++ = standard/library?
=C2=A0

> Of course it could implement it more efficently (as range check in= stead of
> switch if all enumerators are consecutive integers).

One would expect the compilers to be smart enough to do that with a swi= tch=20
block that is contiguous. Still, QoI issue.

--=20
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
=C2=A0 =C2=A0Software Architect - Intel Open Source Technology Center

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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/d4b84145-05e8-452f-ba08-dae9bbe34e04= %40isocpp.org.
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