220 33523 <68a9dd6e-7e33-4e3a-96da-24fe435eda5a@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: wei zhang Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: A more advanced switch Date: Tue, 1 Aug 2017 23:19:39 -0700 (PDT) Lines: 198 Approved: news@gmane.org Message-ID: <68a9dd6e-7e33-4e3a-96da-24fe435eda5a@isocpp.org> References: <34130636.8iyeqGTS6R@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_5202_965121556.1501654779451" X-Trace: blaine.gmane.org 1501654789 32307 195.159.176.226 (2 Aug 2017 06:19:49 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 2 Aug 2017 06:19:49 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDWIFSHO6EDBB7G5QXGAKGQEFOMQZSI@isocpp.org Wed Aug 02 08:19:42 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f70.google.com ([74.125.83.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dcn0J-0007bl-F5 for gclcip-std-proposals@m.gmane.org; Wed, 02 Aug 2017 08:19:35 +0200 Original-Received: by mail-pg0-f70.google.com with SMTP id u7sf40716714pgo.6 for ; Tue, 01 Aug 2017 23:19:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=fxOOrJ/v05g/Tapq4zhk7wfyMybKvMbO9tv7PhnzHXk=; b=OQJfmTF/uAF4BVT7uKHP6I+2RaRqDR/feWmIVphLsIQcEeJef9t1sBXoxCJlN3E11S dHVTf65J1tOv+DgDlNANcohxZhv2eejgUpYyGZoLkfqGdjVY2OUrto8ElQHpMfXIpb+t m4YzCkTIAbyy/5ZxV7SkYf0Z1H5VMNa+4B4F78MtdYYgcVBVRZ8+doh/njDKnEA4BAHG t2EJ+cfkNYxlUObWpW7IkPjWxJxhrzjpQsQoB8VegsRVJobIgWpdjoxUIo7E3z0l6LlZ PFxfEmPwUK9jyQOmkQSqWp8vlnD8zCPnxdPF6tjXiLtnsx5X/2mdOljkh5vCwaKgvckV 1kEA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=fxOOrJ/v05g/Tapq4zhk7wfyMybKvMbO9tv7PhnzHXk=; b=rCHwQkLsMt+kjOWPBSvI1gEavarMvhDF0kQDWSgOv0XljXoUvzPa0WwP/CTDwG8kvH +EvOkZnM8y++ogQIAj1EHFx8/qilwY4p0kmtqIlOYg3ttU2+DhXwMFzHoTEOjqi0BGQq ES713txnyQCU6jAtJ+P+9Vf6d9dJzmDNQOG3NoNuAOgvx9TKUUgm0d4rgoVTAhKD1w6N 1jQtPzagUaXELN1XZviCa49++e+RdoRHUuoPuF4KfnY8EXVsfl4cT6qYxhjj9u4n340X tmwqoSeZspC6GA2t5wnFDS9oOVV0bELUhX0TIdQEr5ApLDrFfX9XtK7W/aHtvTRJPJv7 A0Zw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version: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=fxOOrJ/v05g/Tapq4zhk7wfyMybKvMbO9tv7PhnzHXk=; b=LnjhY4eLTeEVaN4mFw1DlFfCo2rnwtdvBWjVASwFFK0BoGYUrjNcLtiR1ktk1mjG/W I0NifbDLfzqn0FoQ++/NlwiZFri8a5At6EoLx5XZ1t0Ta/vKyjZvWgkMluWyd4XEU+vU ogekg3qI9N4QTNcftyLgtyCuH0RR4dEcPyJgDhxM0vmiv/FoRZCTKCguOO3gmwJfao1d XYNEJWqrpRXbex8eMiJoqCjfebeq+zDUpbxE7cqHgvBaV3z+z+xMYDJ5uJnJdeVedX4W 60lh3Te2i5+2vv+YRMszYc7u3wl3bF0eFBxt3ZZ/1p3YBhUUms5qV3GW+m4IuSuqgFPc 35xQ== X-Gm-Message-State: AIVw113wUvmkpBKOKJ+MgDUxoVAfNpUo4k6iOtDDvj5c8Os5KvEVvhkh wGwkALFprk727Rsq X-Received: by 10.98.11.200 with SMTP id 69mr2762276pfl.21.1501654781176; Tue, 01 Aug 2017 23:19:41 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.43.81 with SMTP id r78ls11851664ior.51.gmail; Tue, 01 Aug 2017 23:19:39 -0700 (PDT) X-Received: by 10.31.153.84 with SMTP id b81mr113475vke.14.1501654779916; Tue, 01 Aug 2017 23:19:39 -0700 (PDT) In-Reply-To: <34130636.8iyeqGTS6R@tjmaciei-mobl1> X-Original-Sender: lala.willzhang@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:33523 Archived-At: ------=_Part_5202_965121556.1501654779451 Content-Type: multipart/alternative; boundary="----=_Part_5203_1138877533.1501654779451" ------=_Part_5203_1138877533.1501654779451 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable We can only add silently with case 5, 6: =E5=9C=A8 2017=E5=B9=B48=E6=9C=882=E6=97=A5=E6=98=9F=E6=9C=9F=E4=B8=89 UTC+= 8=E4=B8=8A=E5=8D=885:34:29=EF=BC=8CThiago Macieira=E5=86=99=E9=81=93=EF=BC= =9A > > On ter=C3=A7a-feira, 1 de agosto de 2017 14:24:04 PDT costeln...@gmail.co= m=20 > =20 > wrote:=20 > > We have to use "case" for every, well, case when specifying a sequence,= =20 > > because it uses fallthrough. We have to use "break" to avoid that. I=20 > find=20 > > this bad. Because of the necessity of using "break" we can't just=20 > "break"=20 > > out of a loop if the switch is inside a loop. Also, if there are=20 > > consecutive cases we have to specify each one of them. Additionally, we= =20 > > could also forget breaking. This "switch" isn't safe and is pretty old.= =20 > >=20 > > In Pawn we can do it a lot better:=20 > > switch( variable )=20 > > {=20 > > case 0 .. 4:=20 > > With GNU extensions to C and C++:=20 > > case 0 ... 4:=20 > > > 1. There's no need for break, there's no fallthrough. Advantage: we can= =20 > > easily "continue" and "break" loops from inside the "switch".=20 > > That can't change now. This HAS been discussed in this list and in std-= =20 > discussions and, just like the non-local breaks, it's very hard to adapt= =20 > the=20 > language grammar to.=20 > > We need a different keyword or some modification keyword to the switch,= =20 > since=20 > there is unmarked code that expects to fall through. We cannot silently= =20 > break=20 > them.=20 > > > I know that it's hard to have features accepted in such a popular=20 > standard,=20 > > but upgrading switch is something that should really be considered !=20 > > C++17's [[fallthrough]] attribute is just as complicated as the=20 > "switch".=20 > > It needs to be added everywhere or else we would get warnings (AFAIK).= =20 > > We've done that in Qt. Not very difficult once the compiler starts=20 > warning.=20 > > The difficult part is to guess whether a fallthrough was intended or a=20 > break was=20 > missing.=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/68a9dd6e-7e33-4e3a-96da-24fe435eda5a%40isocpp.or= g. ------=_Part_5203_1138877533.1501654779451 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
We can only add silently with case 5, 6:




=E5=9C=A8 2017=E5=B9=B48=E6=9C=882=E6=97=A5=E6=98=9F=E6= =9C=9F=E4=B8=89 UTC+8=E4=B8=8A=E5=8D=885:34:29=EF=BC=8CThiago Macieira=E5= =86=99=E9=81=93=EF=BC=9A
On ter= =C3=A7a-feira, 1 de agosto de 2017 14:24:04 PDT costeln...@gmail.com=20
wrote:
> We have to use "case" for every, well, case when specify= ing a sequence,
> because it uses fallthrough. We have to use "break" to a= void that. I find
> this bad. Because of the necessity of using "break" we c= an't just "break"
> out of a loop if the switch is inside a loop. Also, if there are
> consecutive cases we have to specify each one of them. Additionall= y, we
> could also forget breaking. This "switch" isn't safe= and is pretty old.
>=20
> In Pawn we can do it a lot better:
> switch( variable )
> {
> =C2=A0 =C2=A0 case 0 .. 4:

With GNU extensions to C and C++:

=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0case 0 ... 4:

> 1. There's no need for break, there's no fallthrough. Adva= ntage: we can
> easily "continue" and "break" loops from insid= e the "switch".

That can't change now. This HAS been discussed in this list and in = std-
discussions and, just like the non-local breaks, it's very hard to = adapt the=20
language grammar to.

We need a different keyword or some modification keyword to the switch,= since=20
there is unmarked code that expects to fall through. We cannot silently= break=20
them.

> I know that it's hard to have features accepted in such a popu= lar standard,
> but upgrading switch is something that should really be considered= !
> C++17's [[fallthrough]] attribute is just as complicated as th= e "switch".
> It needs to be added everywhere or else we would get warnings (AFA= IK).

We've done that in Qt. Not very difficult once the compiler starts = warning.

The difficult part is to guess whether a fallthrough was intended or a = break was=20
missing.

--=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/68a9dd6e-7e33-4e3a-96da-24fe435eda5a= %40isocpp.org.
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