220 33730 article Path: news.gmane.org!.POSTED!not-for-mail From: Tony V E Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: A more advanced switch Date: Wed, 9 Aug 2017 13:08:14 -0400 Lines: 391 Approved: news@gmane.org Message-ID: References: <574320af-c1ae-4676-883c-ae4e91fcd874@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="001a114a826c1ec62b0556552041" X-Trace: blaine.gmane.org 1502298499 18862 195.159.176.226 (9 Aug 2017 17:08:19 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 9 Aug 2017 17:08:19 +0000 (UTC) To: Standard Proposals Original-X-From: std-proposals+bncBCUZ5QWKNQIP7AVNZQCRUBHSIU7GW@isocpp.org Wed Aug 09 19:08:13 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f200.google.com ([209.85.192.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dfUSp-0004Wd-S6 for gclcip-std-proposals@m.gmane.org; Wed, 09 Aug 2017 19:08:12 +0200 Original-Received: by mail-pf0-f200.google.com with SMTP id r13sf67982044pfd.14 for ; Wed, 09 Aug 2017 10:08:18 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1502298497; cv=pass; d=google.com; s=arc-20160816; b=NXKpfO5+1a+qDIidH+0U526mSwhqck+6p/2T2fPnhxrqPY7FHTNBJyz/pJFKjC72B/ ED2uS/eGa3rFeujeSnXKfnUF4sNSa6ylxW923NROyfrGK3/IrAK1W4vZeUcp/hmxs8zF jPizzwTg4mxQv91fIn8IKwI46Uo25ZQzqJu02PxAOOJDLRzNxQnVOHOZAx+2IbLiwcHy /0rl/xnxkixZb80GdPIJ3JV/CE4keaLSzCHrFbeuGqMVQJuwTZ8QJbXVY1SZlfZ3JIKV pua+3dvc6MKTLPBrHrNVA5gTvURO8mk3o4HdFBSXhk3FjwBmlbfVEtQ3K4yZANPx2D4+ Rq7g== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:reply-to:to:subject:message-id:date :from:references:in-reply-to:mime-version:arc-authentication-results :arc-message-signature:dkim-signature:arc-authentication-results; bh=W5X//ncwEhMjWPRBwXXf6R3q0Z/TDAAH/Fd+W3mE5jg=; b=OkqxQShaKivti7Z4+ykWv9ZGzBLP4Su5ZQZmWX2V9sTMHYUqZ5OffDLeDKbW+t/fzf oCl5CJRAwKUGKiTD7rsNGBbvxZlAXKA4By7Ksg6Ld//3stVI2/Kohf+gYGPH5FK+pETS DrjAm3jO2DaiQdCl2grFOxaXsjqKzZwbEfLu2rQj9Xm0MNYsHjLVLflyEUf81BTEs9ig lB+liTnS8uVT0j02us84pQp4ZrjjIIVTGJ7onfCWdfar9LikEUvTdSpTVadMnuf7N/50 4lC6iYxsw6rzLseX4j+kS0JtKL8CKHfh4QsRUNS9wvo1Mk6SryeWdoHq26Ix1B/k5j++ l5vw== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=GX9EqREK; spf=pass (google.com: domain of tvaneerd@gmail.com designates 2607:f8b0:400d:c09::235 as permitted sender) smtp.mailfrom=tvaneerd@gmail.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=W5X//ncwEhMjWPRBwXXf6R3q0Z/TDAAH/Fd+W3mE5jg=; b=pi0mST4mZUNvDb5fgZwdWVMVMOX5rpr09zcu+UV+8go1xnD0k0iDd1yvBH/OmwJxCS EidEED2KSlliNTNwRsJ6RFaTQDPm+x8LlujpADLcdc+NjUE2KknpSXjpxLRykMKQTd86 VRPk4Ah1Dn7rYE+hSrM/NypVLEtGoJpYtbimQzylA4oDuHOFCLVE8WtGsGaRzNKQoRP1 6GuqOen7KJ7Krmf7qThcTWz6YCodifr7WwKShgeqtqERgrhk6hHGuIeq1aQ5C0PrSDnT xJoxQXAyFSk/+kxkElspgz/vkHXHGoudn+FWgPEc0CDTlXVKY4GZ+/u+OItXyRFe9lz6 03zw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=W5X//ncwEhMjWPRBwXXf6R3q0Z/TDAAH/Fd+W3mE5jg=; b=TlkG1AUBJXfs0T6QijakRif76obrTc9gqfgq7I05En3Wk99N/PYGnu5L1Dc+rRWWFJ u8U58yunpiP10l5svGWmYaI9n0R+hKDLGQNCqBiOrEwVYhlkv1ukib5r62ezSqNo8vwD thtiIOVWKC0eUfxIS3Q0UBREHGwzeaxGgFLjInQhVwa0v7qmc4Ehs2EH1IF8gEzBwKK/ BEdlQqAcX02Bardlv3FTVt4SfSoCZg0LN6T/ChenTCF8rtFl+LlbNvlzl0gIyFu6hEha scTFnoS1Yd5cvu0lpmQNPdBprJ9KN3lMlvqDeCRoLyIy8YnOAzf174yqg7wbjEi83HXT 0KFw== X-Gm-Message-State: AHYfb5jy3mCBdoVrXuY7tQnxlKLT0wc/EyFgGsv2peszsInxR5YrFxSW WiwOYEiQUkOzjkMH X-Received: by 10.99.0.19 with SMTP id 19mr5648364pga.48.1502298497534; Wed, 09 Aug 2017 10:08:17 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.192.65 with SMTP id u62ls5682482itf.2.gmail; Wed, 09 Aug 2017 10:08:15 -0700 (PDT) X-Received: by 10.237.36.155 with SMTP id t27mr11053158qtc.314.1502298495052; Wed, 09 Aug 2017 10:08:15 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1502298495; cv=none; d=google.com; s=arc-20160816; b=iMOFt7hwxOFIZeOceKNgucjj/tr9taZz63EG394AM6ZpQ1CvUmRDlecUEo1jepSdJn FtctRg5xDVGBwYN1RJfAJj4I7TJmGzESO/e1achuHRQs1HmytfIr3zGtUYxWnXvXHr4/ XaFgxfIOhUCqCKLFgeiI3j1f7FMDrywA4l2SQwljGc/x9CnGP69L63LLYa60lRYXWGxC n5mMqZhloTzVTMVdtnt7J6vkwowDE5g4MInutDpoKGjrh1d9PkaIWcdgITgjww9E59i5 LPVnaX7wSbtMh0/PmJz+uwex0Rb7ewBV7hxuYBuQYd1Wpj9kTo/5WTavCA98BegLX2YE tNKw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=to:subject:message-id:date:from:references:in-reply-to:mime-version :dkim-signature:arc-authentication-results; bh=ReBid/ESmIHms7BB8iefgAnK7WLDmLJ1TlKrJ2H2pR4=; b=E73P0SOxPxVWASfmM3rVf0qnmLcz5RoWNi+CZywqQnfLfnTWjgCkgTXiR8+W05ZZkC M7gEz/nnzE5MrHIzEBFXXyIyFx5Xcat8A9XPx2IA4Di238ur5EfsB4xKlRgTdNltN5aY FIgo87MebS3x8qy0WwvdrzL47WLfK8xLJW/dnclbrF0YjzSnLVlg4nfZ+9phmpCUDFHd XObfe3UHUCWYpknlFoDna3sR8dcyrHlHQqZvaK2cSMsEml4GEKIcjrO5disKj5yClD3C 9xUUPB6G4LHhRsABuTJ3OpTjg/e/aFYpqjBbcTJkn/neMxMXkJO7XDFCsVWEaIeDIOF5 xOXg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=GX9EqREK; spf=pass (google.com: domain of tvaneerd@gmail.com designates 2607:f8b0:400d:c09::235 as permitted sender) smtp.mailfrom=tvaneerd@gmail.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=gmail.com Original-Received: from mail-qk0-x235.google.com (mail-qk0-x235.google.com. [2607:f8b0:400d:c09::235]) by mx.google.com with ESMTPS id s57si3352569qtc.220.2017.08.09.10.08.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Aug 2017 10:08:15 -0700 (PDT) Received-SPF: pass (google.com: domain of tvaneerd@gmail.com designates 2607:f8b0:400d:c09::235 as permitted sender) client-ip=2607:f8b0:400d:c09::235; Original-Received: by mail-qk0-x235.google.com with SMTP id d145so39737734qkc.2 for ; Wed, 09 Aug 2017 10:08:15 -0700 (PDT) X-Received: by 10.55.74.142 with SMTP id x136mr10432836qka.254.1502298494648; Wed, 09 Aug 2017 10:08:14 -0700 (PDT) Original-Received: by 10.237.42.10 with HTTP; Wed, 9 Aug 2017 10:08:14 -0700 (PDT) In-Reply-To: <574320af-c1ae-4676-883c-ae4e91fcd874@isocpp.org> X-Original-Sender: tvaneerd@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=GX9EqREK; spf=pass (google.com: domain of tvaneerd@gmail.com designates 2607:f8b0:400d:c09::235 as permitted sender) smtp.mailfrom=tvaneerd@gmail.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=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:33730 Archived-At: --001a114a826c1ec62b0556552041 Content-Type: text/plain; charset="UTF-8" break by default is fine, how do I opt-out within switch break, or is it all or nothing? switch break(x) { case 1: case 2: foo(); case 3: bar(); case 4: etc(); } How do I get fallthru on case 1 to 2? P.S. I think the only way we get a new switch statement is by a big change - pattern matching. No one wants to do incremental changes to switch. But some of these questions need to be answered either way. P.P.S. to the other question of > > switch (s) > { > case "A": > case "B": > default: > } > I've seen C code do this, where s was a char *. (And s was typically pointing to static chars, like s = "B") So you have a pointer s, which is just an int, right? And all the cases are compile/link time constants... I'm not sure that was valid C, but it worked. Many years ago. Tony On Wed, Aug 9, 2017 at 9:08 AM, wrote: > > I would very much like to see some changes to switch. > > I'd like something like: > > switch break (x) // cases break by default; > { > case 1: whatever(); > case 2: whatever(); > } > > I'd also like, for at least this variation of switch, for a case to be a > scope by default, such that is ok: > So that variables can be declared without requiring more braces. > > switch break (x) // cases break by default; > { > case 1: int z = 1; whatever(z); // not an error > case 2: whatever(); > } > > I think this would make most switch statements a lot less verbose. > It seems a lot of the flexibility of the classic switch just isn't > required. > So this switch could be used when it's not and the existing switch can be > used when it is. > > switch break seems easy to teach to me. So why not? > > > > On Wednesday, August 2, 2017 at 9:24:04 AM UTC+12, costeln...@gmail.com > wrote: > >> Hello, I'm sorry if you talked about this here before, but I didn't watch >> this group and I couldn't find this thing when searching. >> >> I'm coming from another language named Pawn, it looks like C ~80%, but it >> has more advantages than C. Here's the official page: >> https://www.compuphase.com/pawn/pawn.htm . >> >> A problem in C++: "switch" is exactly like in C, I think it deserves an >> upgrade, as it can be used a lot, providing more speed and easier syntax >> than lots of "if" ... "else if" ... "else" lines. I know that simply >> updating it would break compatibility, so it may require another name >> instead of switch, or you can find any other backwards compatible >> alternative. I bet you can do this perfectly. >> >> For cases 0, 1, 2, 3, 4 and 5, 6 and "default" in C++ we have to do it >> like >> switch( variable ) >> { >> case 0: case 1: case 2: case 3: case 4: >> { >> // ... >> break; >> } >> >> case 5: case 6: >> { >> // ... >> break; >> } >> >> default: >> { >> // ... >> } >> } >> >> We have to use "case" for every, well, case when specifying a sequence, >> because it uses fallthrough. We have to use "break" to avoid that. I find >> this bad. Because of the necessity of using "break" we can'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. Additionally, we >> could also forget breaking. This "switch" isn't safe and is pretty old. >> >> In Pawn we can do it a lot better: >> switch( variable ) >> { >> case 0 .. 4: >> { >> // ... >> } >> >> case 5, 6: >> { >> // ... >> } >> >> default: >> { >> // ... >> } >> } >> >> 1. There's no need for break, there's no fallthrough. Advantage: we can >> easily "continue" and "break" loops from inside the "switch". >> 2. We can use ".." if using several cases that are consecutive in the >> same block of code, to specify an interval. >> >> I know that it's hard to have features accepted in such a popular >> standard, but upgrading switch is something that should really be >> considered ! C++17's [[fallthrough]] attribute is just as complicated as >> the "switch". It needs to be added everywhere or else we would get warnings >> (AFAIK). >> >> C++ needs a lot more syntactic sugar. Small and nice things are making >> the language more likeable. I think that you should watch other languages >> too for interesting small features. >> > -- > 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/574320af-c1ae-4676- > 883c-ae4e91fcd874%40isocpp.org > > . > -- Be seeing you, Tony -- 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/CAOHCbisLgTxLz75Em3Had35AecQrtpRZKFWRaMXUZsSVtN7Fng%40mail.gmail.com. --001a114a826c1ec62b0556552041 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
break by default is fine, how do I opt-out within switch b= reak, or is it all or nothing?

switch break(x)
{
c= ase 1:
case 2:
=C2=A0=C2=A0=C2=A0 foo();
case 3:=
=C2=A0=C2=A0=C2=A0 bar();
case 4:
=C2=A0=C2=A0= =C2=A0 etc();
=C2=A0}


How do I get fallthru on case 1 t= o 2?


P.S. I think the only way we get a new switch stateme= nt is by a big change - pattern matching.
No one wants to do incre= mental changes to switch.
But some of these questions need to be a= nswered either way.

P.P.S. to the other question of

>
> switch (s)
> {
> case "A":
> case "B":
> default:
> }
>

I've seen C code do t= his, where s was a char *. (And s was typically pointing to static chars, l= ike s =3D "B")
So you ha= ve a pointer s, which is just an int, right?
And all the cases are compi= le/link time constants...
I'm not sure that was valid C, but it work= ed.=C2=A0 Many years ago.

Tony
=


On Wed, Aug 9, 2017 at 9:08= AM, <gmisocpp@gmail.com> wrote:

I would ve= ry much like to see some changes to switch.

I'= d like something like:

switch break (x) // cases b= reak by default;
{
=C2=A0=C2=A0=C2=A0 case 1: whatever(= );
=C2=A0=C2=A0=C2=A0=C2=A0case 2: whatever();
}
I'd also like, for at least this variation of switch,=C2=A0= for=C2=A0a case=C2=A0to be a scope by default, such that is ok:
S= o that variables can be declared without requiring more braces.
<= br>
switch break (x) // cases break by default;
{<= /div>
=C2=A0=C2=A0=C2=A0 case 1: int z =3D 1; whatever(z); // not an er= ror
=C2=A0=C2=A0=C2=A0=C2=A0case 2: whatever();
}
I think this would make most switch statements a lot less verb= ose.
It seems a lot of the flexibility of the classic switch just= isn't required.
So this switch could be used when it's n= ot and the existing switch can be used when it is.

switch break seems easy to teach to me. So why not?



On Wednesday, August 2, 2017 at 9:24:04 AM UTC+12, costeln...@gmail.com wrote:
Hello, I'm sorry i= f you talked about this here before, but I didn't watch this group and = I couldn't find this thing when searching.


A p= roblem in C++: "switch" is exactly like in C, I think it deserves= an upgrade, as it can be used a lot, providing more speed and easier synta= x than lots of "if" ... "else if" ... "else" = lines. I know that simply updating it would break compatibility, so it may = require another name instead of switch, or you can find any other backwards= compatible alternative. I bet you can do this perfectly.

For cases 0, 1, 2, 3, 4 and 5, 6 and "default" in C++ we have t= o do it like
switch( variable )
{
=C2=A0 =C2=A0 case 0: case 1<= /span>: case 2= : case 3: case 4:
=C2=A0 = =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 // ...
=C2=A0 = =C2=A0 =C2=A0 =C2=A0 break= ;
=C2=A0 =C2=A0 }

=C2=A0 =C2=A0 case 5: case 6:
=C2=A0 =C2=A0 {
=C2= =A0 =C2=A0 =C2=A0 =C2=A0 // ...
=C2=A0 =C2=A0 =C2=A0 =C2=A0 break;
=C2=A0 =C2=A0 }

=C2=A0 =C2=A0 defaul= t:
=C2=A0 =C2=A0 {<= /span>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 // ...
=C2=A0 =C2=A0 }
}

We have to use &qu= ot;case" for every, well, case when specifying a sequence, because it = uses fallthrough. We have to use "break" to avoid that. I find th= is bad. Because of the necessity of using "break" we can't ju= st "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. Additiona= lly, we could also forget breaking. This "switch" isn't safe = and is pretty old.

In Pawn we can do it a lot bett= er:
switch= ( variable )
{=
=C2=A0 =C2=A0 case 0= .. 4:
=C2=A0 = =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 // ...
=C2=A0 = =C2=A0 }

=C2=A0 =C2=A0 case 5, 6:
=C2=A0 =C2=A0 {
= =C2=A0 =C2=A0 =C2=A0 =C2=A0 // ..= ..
=C2=A0 =C2=A0 }
=C2=A0 =C2=A0 default:=
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 // ...=C2=A0 =C2=A0 }
}=

1. There's no ne= ed for break, there's no fallthrough. Advantage: we can easily "co= ntinue" and "break" loops from inside the "switch"= ..
2. We can use ".." if using several cases that are co= nsecutive in the same block of code, to specify an interval.

=
I know that it's hard to have features accepted in such a po= pular standard, but upgrading switch is something that should really be con= sidered ! C++17's [[fallthrough]] attribute is just as complicated as t= he "switch". It needs to be added everywhere or else we would get= warnings (AFAIK).

C++ needs a lot more syntactic = sugar. Small and nice things are making the language more likeable. I think= that you should watch other languages too for interesting small features.<= /div>

--
You received this message because you are subscribed to the Google Groups &= quot;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/5743= 20af-c1ae-4676-883c-ae4e91fcd874%40isocpp.org.



--
Be seeing you,
Tony

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
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 htt= ps://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAOHCbisLgTxLz75E= m3Had35AecQrtpRZKFWRaMXUZsSVtN7Fng%40mail.gmail.com.
--001a114a826c1ec62b0556552041-- .