220 37123 <4b81b3b8-5def-4003-b073-89af676e837a@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: jsaintmartin356@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: pseudo constness Date: Wed, 28 Feb 2018 12:30:40 -0800 (PST) Lines: 149 Approved: news@gmane.org Message-ID: <4b81b3b8-5def-4003-b073-89af676e837a@isocpp.org> References: <1519283315.58210.23.camel@gmail.com> <0a7e7e42-aa28-4632-8e66-56b0633755ba@isocpp.org> <27b5c95c-5b44-4089-bb14-b2d1b806093b@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_6126_1363222138.1519849840991" X-Trace: blaine.gmane.org 1519849721 24496 195.159.176.226 (28 Feb 2018 20:28:41 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 28 Feb 2018 20:28:41 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBD2KVY7D7YJBB4NC3TKAKGQERZLWMOI@isocpp.org Wed Feb 28 21:28:37 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f198.google.com ([209.85.217.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1er8L7-0005s6-3q for gclcip-std-proposals@m.gmane.org; Wed, 28 Feb 2018 21:28:37 +0100 Original-Received: by mail-ua0-f198.google.com with SMTP id g9sf2243315ual.8 for ; Wed, 28 Feb 2018 12:30:43 -0800 (PST) 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=YqT75ANFQvSIPj8coXah5iUTHBLb6NAWsIJEg2h660g=; b=sz1uHPXjKjVMizQ2J1Z/tEbi5JPhiDUcWuY6eB9AiccSX3TDgMKsAkewBl7Ik689RF MbOkRhEuwG/bFKd4FWaRhor6quoZJvExQlIS7sXVLAVfodRxMXcuMNf/qdloofe7iz67 t04SbzJ86tUPEftCVdinB6ARxLgU97GglAi7uUr7hb9zjG667x3+K2QURq2D/owhPcp2 HE96tdLse4u7WcwNyvdqn9SyfTNLTyvPz9L8v/uay/Nn0NoBWOnS9gh63nY8VW9reak0 Ka22/sAz9fTisDFSgZ6fNXRaVMQs5KznnwiS9mzD+llAnZa8Shzoy46fFp3A2q03Db/p N3pg== 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=YqT75ANFQvSIPj8coXah5iUTHBLb6NAWsIJEg2h660g=; b=cpyI5AKqkSqslaVx6blyIuSNFLfj2BUS3K88hJsUnwF/K8ZdbrGymhg0hUbSH0uEin rrMPqTJhENeaSP/LQD5npgCamwmLBKY3fJUE6+JtOUjUvX+dlNc6qtOk4ORu/EcWF+du XGrqEKkzQ42EIbgvt7jfIeGTZRwbgAVoIGNY8E4DUpvVa1gK0J5E7MLFEiABWJQU/AbO ibL2SYsp2nM0DFh+BUZIHgpN4VcKbZOdhnNmvlUXYcW8TirsdRbhpgC3NBqM7LyWHh4R ENQs52Nd5pe0CcCowNy5mAs6y2Lased+LEgLTJPRK0l1XK8aaTOb46n+1O8KWsUZLYtt mldA== 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=YqT75ANFQvSIPj8coXah5iUTHBLb6NAWsIJEg2h660g=; b=G/cJU9W2YA6fwjCrXKOvfcCfz7VJVK/1gE0KO7/F/YQ5+qPo8lNYl7xNHstnL0SNfF elsEjydDORAhMfJA2zt8FVYG8bsI65NnJSzvM7EqB5qvbk0aOqKs5j9/WVze4jTmTeP6 PBs9TWNAZ8Ffdx/f2xFWMMsC6GI8GmIuJSxBh8uD319iLA0zjQ7HYsGGgqxQVe3Ixmy/ MmMSfbfwMmFWrfD1pWsxl2WjCH73NbU0dFqUREmmiKHclxwhLcwV+X/s0Pv9G0AXgp27 FmALF2TDCFE4P/+CaV7zOrWDqnYfhjk5qGn7yFowWoHeOpY9yoLgAA8a67p1tz7Pg9kB dqQA== X-Gm-Message-State: APf1xPDJvKZc0uKY4k85OJ3gIbosIp5pfzUlPvb1ybeGZiSiH2oKFcDn oMmjfkJ/Am8XGoQtU/9T3Qqiug== X-Google-Smtp-Source: AG47ELsgHOpE/L+THb7/7co6nRtVsVqXgQHMOh9Q8hSPnl50S4Qz/DRAauP1094eqvVNshqFNh69lQ== X-Received: by 10.176.9.208 with SMTP id e16mr7776697uah.27.1519849843256; Wed, 28 Feb 2018 12:30:43 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.196.71 with SMTP id u68ls2409951vkf.5.gmail; Wed, 28 Feb 2018 12:30:41 -0800 (PST) X-Received: by 10.31.180.79 with SMTP id d76mr1934494vkf.7.1519849841575; Wed, 28 Feb 2018 12:30:41 -0800 (PST) In-Reply-To: X-Original-Sender: jsaintmartin356@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:37123 Archived-At: ------=_Part_6126_1363222138.1519849840991 Content-Type: multipart/alternative; boundary="----=_Part_6127_928035103.1519849840992" ------=_Part_6127_928035103.1519849840992 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Another use of pseudoconst / reversible would allow to use hint to find an= =20 element in map within a pseudo const method. As far as I know, m.insert (ihint, p) exists,=20 but not map.find (ihint, p) With peudo const, you could write your pseudoconst find, like this, if you= =20 are certain -1 is not a second existing in the map, and map.erase (i) was= =20 defined as the reverse of insert (i) : std::map::iterator find (std::map& m,=20 std::pair& p) reversible { std::pair p2 .(p.first, (size_t) -1); m.insert (ihint, p); if (ihint->second =3D=3D (size_t) -1) { m.erase (ihint); ihint =3D m.end (); } return ihint; } =20 " On Friday, February 23, 2018 at 1:27:03 PM UTC+1, Jake Arkinstall wrote: > > On 23 Feb 2018 08:58, "J=C3=A9r=C3=B4me Saint-Martin" > wrote: > > pseudo const Is an indication to users : "the method should not change th= e=20 > object".=20 > > > *Const* is an *guarantee* to users: the method *does* not change the=20 > object. A pseudoconst method would also have to guarantee this or the=20 > proposal wouldn't be useful at all. So, once again, come up with a way of= =20 > guranteeing that a modification is reversed. A "reversible" or similar=20 > keyword would be more interesting. All it needs to do is only permit a=20 > series of commands and functions that are themselves reversible (ones tha= t=20 > lose no information, so type limitations must be considered - see, for=20 > example, http://cpp.sh/9fet5 and http://cpp.sh/9redh ), in the same way= =20 > that const only permits use of operations that are also const. Then you= =20 > need something built into the language that does the reversing. > > This could be useful in a variety of situations. One of which would be an= =20 > enforceable pseudoconst. > "=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/4b81b3b8-5def-4003-b073-89af676e837a%40isocpp.or= g. ------=_Part_6127_928035103.1519849840992 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Another use of pseudoconst / reversible would allow to use= hint to find an element in map within a pseudo const method. As far as I k= now,
m.insert (ihint, p) exists,
but not map.find (ihint, p)

= With peudo const, you could write your pseudoconst find,=C2=A0 like this, i= f you are certain -1 is not a second existing in the map, and map.erase (i)= was defined as the reverse of insert (i) :

std::map<size_t, size= _t>::iterator find (std::map<size_t, size_t>& m, std::pair<= size_t, size_t>& p)=C2=A0 reversible {
=C2=A0 std::pair<size_t= , size_t> p2 .(p.first, (size_t) -1);
=C2=A0 m.insert (ihint, p);
= =C2=A0 if (ihint->second =3D=3D (size_t) -1) {
=C2=A0=C2=A0=C2=A0 m.e= rase (ihint);
=C2=A0=C2=A0=C2=A0 ihint =3D m.end ();
=C2=A0 }
=C2= =A0 return ihint;
}
=C2=A0


"
On Friday, February = 23, 2018 at 1:27:03 PM UTC+1, Jake Arkinstall wrote:
On 23 Feb 2018 08:58, "J=C3=A9r=C3=B4me Saint-Martin" <jsaintm...= @gmail.com> wrote:
pseudo const Is an indication to users : "the method should not chang= e the object".=C2=A0

Const is an guarantee to use= rs: the method does=C2=A0not change the object. A pseudoconst method= would also have to guarantee this or the proposal wouldn't be useful a= t all. So, once again, come up with a way of guranteeing that a modificatio= n is reversed. A "reversible" or similar keyword would be more in= teresting. All it needs to do is only permit a series of commands and funct= ions that are themselves reversible (ones that lose no information, so type= limitations must be considered - see, for example, http://cpp.sh/9fet5 and http://cpp.sh/9redh ), in the same way that const= only permits use of operations that are also const. Then you need somethin= g built into the language that does the reversing.
<= br>
This could be useful in a variety of situations.= One of which would be an enforceable pseudoconst.
=
"

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