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Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Variable declarations inside test before block Date: Thu, 04 Dec 2014 18:58:48 +0100 Lines: 510 Approved: news@gmane.org Message-ID: <5480A0D8.2020609@wanadoo.fr> References: <1b00c799-b47e-48b7-8717-9953b1845cca@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------000904090105090508000106" X-Trace: ger.gmane.org 1417715940 26103 80.91.229.3 (4 Dec 2014 17:59:00 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 4 Dec 2014 17:59:00 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBBWWBQKSAKGQED6KXYAI@isocpp.org Thu Dec 04 18:58:51 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ee0-f71.google.com ([74.125.83.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Xwafz-0005dW-7R for gclcip-std-proposals@m.gmane.org; Thu, 04 Dec 2014 18:58:51 +0100 Original-Received: by mail-ee0-f71.google.com with SMTP id c13sf11438022eek.2 for ; Thu, 04 Dec 2014 09:58:50 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :subject:references:in-reply-to:content-type: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=SxeKoKmZ2Yw5m25fJbRpv9G3fa/LSZ+654aKi4mU7vY=; b=BJxds5WiDqDSITfgR+BvwXqmhI8/qoHAxN/WnOWD43g9r5pPt8NENXO47fQS5bZ+PW a/47Woo32AIOgZUyBOV4UEy+XyVofJj5DSAOSwIBrtD/Oh7G73gXLbbBol8NCrE/Ky7c S8wLH0rrKEaRAPkar4l3mHUAC/2tjR9pWC5XTFsMvZGPFpHDT6k5wkwIl2mudVtTXK7H QFLb7y0lB9mzdIFKGIRm1uolgFC0+WWOLpgW03yEmLVUqFmyGOH1hi7+JWGf0KAlO7OH T9+1E8uWcri+U5JABYB85rG/F2iC8c7ugiGv+zFftfSrgRKic07x6udXlFR35Jty60Wn YWog== X-Gm-Message-State: ALoCoQmEEhZfoHWOBkZCrqQ6RTyawEcWEn3lC+40/p8gbkF+4kiI4ExUu/WJRU5ZqjbgYf7c5QDN X-Received: by 10.112.159.199 with SMTP id xe7mr3296lbb.21.1417715930873; Thu, 04 Dec 2014 09:58:50 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.89.100 with SMTP id bn4ls103772wib.47.gmail; Thu, 04 Dec 2014 09:58:49 -0800 (PST) X-Received: by 10.194.170.232 with SMTP id ap8mr18027979wjc.2.1417715929735; Thu, 04 Dec 2014 09:58:49 -0800 (PST) Original-Received: from smtp.smtpout.orange.fr (smtp08.smtpout.orange.fr. [80.12.242.130]) by mx.google.com with ESMTP id ex8si45944672wjb.33.2014.12.04.09.58.49 for ; Thu, 04 Dec 2014 09:58:49 -0800 (PST) Received-SPF: none (google.com: vicente.botet@wanadoo.fr does not designate permitted sender hosts) client-ip=80.12.242.130; Original-Received: from new-host.home ([92.139.157.31]) by mwinf5d43 with ME id PVyo1p00E0gveUk03Vyoya; Thu, 04 Dec 2014 18:58:49 +0100 X-ME-Helo: new-host.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Thu, 04 Dec 2014 18:58:49 +0100 X-ME-IP: 92.139.157.31 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 In-Reply-To: <1b00c799-b47e-48b7-8717-9953b1845cca@isocpp.org> X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=none (google.com: vicente.botet@wanadoo.fr does not designate permitted sender hosts) smtp.mail=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:14857 Archived-At: This is a multi-part message in MIME format. --------------000904090105090508000106 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Le 04/12/14 08:09, squelart@gmail.com a =C3=A9crit : > On Wednesday, December 3, 2014 7:37:24 PM UTC+11, Andrzej Krzemie=C5=84sk= i=20 > wrote: > > W dniu =C5=9Broda, 3 grudnia 2014 05:21:27 UTC+1 u=C5=BCytkownik > sque...@gmail.com napisa=C5=82: > > (First time here, please let me know if I'm doing anything wrong!= ) > > Just a quick idea I couldn't find elsewhere with a quick > search, I was wondering if it had already been proposed and/or > rejected: > > Would it be possible and useful to allow variable declarations > inside a test preceding a block, and make these variables > visible inside the remainder of the test and the block? > (The "remainder of the test" part might be going too far?) > The goal is to avoid polluting a block with variables that are > really only needed inside an inner block. > > E.g.: > | > if((autototal <(automax =3DgetMax())-(autobuffer =3Dmax /3))>1){ > // 'total', 'max' and 'buffer' are visible in this block and > destructed at the end. > } > > while(nullptr!=3D(void*buffer =3Dmalloc(8))){foo(buffer);} > > for(inti =3D0;i <(intend=3D10);++i){cout < > switch(charc =3Dgetchar()){case'\0':break;default:cout < > autof =3D(P*p =3DmaybeP())?p->foo():0;// Too far again? > | > > Any pointers/suggestions/criticisms welcome. > I'd be happy to work on it further if there's any interest. > > Note that some of the above constructs are already valid in C++. > | > | > while(void*buffer =3Dmalloc(8))// > foo(buffer);// valid C++ > > for(inti =3D0,end=3D10;i {cout < > switch(charc =3Dgetchar())// valid C++ > { > case'\0':break; > default:cout < } > > for(iter.init();int*i =3Diter.next();)// valid C++ > use(*i); > | > > |Your proposal offers only a bit more. The question is, whether > the added value counterweights the costs of standardization > effort, complicating the language, more rules for programmers to > learn, compiler updates, etc. My personal answer (based on > feelings and intuition only) is that it is not worth it. > > Regards, > &rzej > > > Thanks for your help, I didn't know about some of these. Always learning! > > I knew about "while (void* p =3D ...)", but it means the variable can=20 > only be tested for "falsiness", you can't have a test that declares a=20 > variable and compares it to an arbitrary non-false value. > while ((void* p =3D ...) =3D=3D 0) ... > But as you say, it's "only a bit more", so it's probably not worth the=20 > huge effort to change the language just for that... > Agreed, Vicente --=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. --------------000904090105090508000106 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Le 04/12/14 08:09, squelart@gmail.com = a =C3=A9crit=C2=A0:
On Wednesday, December 3, 2014 7:37:24 PM UTC+11, Andrzej Krzemie=C5=84ski wrote:
W dniu =C5=9Broda, 3 grudnia 2014 05:21:27 UTC+1 u=C5=BCytkownik sque...@gmail.com napisa=C5=82:
(First time here, please let me know if I'm doing anything wrong!)

Just a quick idea I couldn't find elsewhere with a quick search, I was wondering if it had already been proposed and/or rejected:

Would it be possible and useful to allow variable declarations inside a test preceding a block, and make these variables visible inside the remainder of the test and the block?
(The "remainder of the test" part might be going too far?)
The goal is to avoid polluting a block with variables that are really only needed inside an inner block.

E.g.:
if ((auto total < (auto max =3D getMax()) - (auto buffer =3D max / 3)) > 1) {
=C2=A0 =C2=A0 // = 'total', 'max' and 'buffer' are visible in this block and destructed at the end.
}

while (nullptr !=3D (void* buffer =3D malloc(8))) { foo(buffer); }

for (int i =3D 0; i < (int end =3D 10); ++i) { cout << end - i; }

switch (char c =3D getchar()) { case '\0': break; default: cout << c; }

auto f =3D (P* p =3D maybeP()) ? p->foo() : 0; // Too far again?

Any pointers/suggestions/criticisms welcome.
I'd be happy to work on it further if there's any interest.
=C2=A0
Note that some of the above constructs are already valid in C++.
while (void* buffer =3D malloc(8)) //
=C2=A0 foo(buffer); =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 // valid C++

for (int i =3D 0, end =3D 10; i < end; ++i) // different than your example
{ cout << end - i; } =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0// but similar functionality

switch (char c =3D getchar()) =C2=A0// valid C++
{
case '\0': break;
default: cout << c;
}

for (iter.init(); int* i =3D iter.next();) // valid C++
=C2=A0 use= (*i);

Your proposal offers only a bit more. The question is, whether the added value counterweights the costs of standardization effort, complicating the language, more rules for programmers to learn, compiler updates, etc. My personal answer (based on feelings and intuition only) is that it is not worth it.

Regards,
&rzej

Thanks for your help, I didn't know about some of these. Always learning!

I knew about "while (void* p =3D ...)", but it means the variable can only be tested for "falsiness", you can't have a test that declares a variable and compares it to an arbitrary non-false value.

while ((void* p =3D ...) =3D=3D 0) ...
But as you say, it's "only a bit more", so it's probably not worth the huge effort to change the language just for that...

Agreed,
Vicente

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