220 18820 article Path: news.gmane.org!not-for-mail From: Christopher Jefferson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Compressing std::optional Date: Fri, 26 Jun 2015 21:49:24 +0100 Lines: 56 Approved: news@gmane.org Message-ID: References: <4359ebfb-5e20-42c1-84a0-16ef6201db33@isocpp.org> <33303ec4-d4c3-4080-a7bb-346496e38114@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1435351770 19753 80.91.229.3 (26 Jun 2015 20:49:30 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 26 Jun 2015 20:49:30 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCF5NPH6QMFRBVPVW2WAKGQEHJIG3GA@isocpp.org Fri Jun 26 22:49:30 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wi0-f197.google.com ([209.85.212.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Z8aYw-0004pi-MT for gclcip-std-proposals@m.gmane.org; Fri, 26 Jun 2015 22:49:26 +0200 Original-Received: by wiws10 with SMTP id s10sf8093886wiw.2 for ; Fri, 26 Jun 2015 13:49:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type:content-transfer-encoding :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=7CAJ9ibolANtHoFK0rY5MvhpII1sFdJWY1lECSlUqMw=; b=T4AMaDARafzoaBdu+S9TWMPbrgE4QCmwRECM858Zfcmye4umhLO56s61AoKNVKUbWP CzdAJQN64iz48KBbPIHFFzHhDzz1c8b5RUukUpSMzH87AXxrOJK5eDKBDaN/vQ04+M06 dsyAvgwkjlJRKF3Gm/309rALsaMfWAU8a2nOasYzGsNbkbEXCwjDNCrPFMVr1f8kDu8s Zk9Gx+oCaq4feL9vnv8txktMYt57F4NNCw0SlDawadhsy/H1WluVtGmw9b2PK1tD6t/r Q/767Zich61t7DkWuFo7Yy1ocSxa8DUswUUikXBs6gYQ+rcKcr9djdBS2cCwibPPyd1H X-Gm-Message-State: ALoCoQlbtoMlvqaeKHjLTI1vuG9aVcmuPstEKuYApIRHeEbWxcGf+a9YKkcomtkX9stswpMy8rG7 X-Received: by 10.112.40.45 with SMTP id u13mr2364704lbk.0.1435351766238; Fri, 26 Jun 2015 13:49:26 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.29.36 with SMTP id g4ls615994lah.33.gmail; Fri, 26 Jun 2015 13:49:24 -0700 (PDT) X-Received: by 10.112.125.65 with SMTP id mo1mr3377003lbb.0.1435351764688; Fri, 26 Jun 2015 13:49:24 -0700 (PDT) Original-Received: from mail-lb0-f182.google.com (mail-lb0-f182.google.com. [209.85.217.182]) by mx.google.com with ESMTPS id pt2si28354474lbb.46.2015.06.26.13.49.24 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Jun 2015 13:49:24 -0700 (PDT) Received-SPF: neutral (google.com: 209.85.217.182 is neither permitted nor denied by best guess record for domain of chris@bubblescope.net) client-ip=209.85.217.182; Original-Received: by lbbwc1 with SMTP id wc1so71301760lbb.2 for ; Fri, 26 Jun 2015 13:49:24 -0700 (PDT) X-Received: by 10.152.246.37 with SMTP id xt5mr3232033lac.83.1435351764193; Fri, 26 Jun 2015 13:49:24 -0700 (PDT) Original-Received: by 10.112.13.198 with HTTP; Fri, 26 Jun 2015 13:49:24 -0700 (PDT) In-Reply-To: X-Original-Sender: chris@bubblescope.net X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 209.85.217.182 is neither permitted nor denied by best guess record for domain of chris@bubblescope.net) smtp.mail=chris@bubblescope.net 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:18820 Archived-At: On 26 June 2015 at 21:22, Tony V E wrote: > > > On Fri, Jun 26, 2015 at 4:20 PM, Christopher Jefferson > wrote: >> >> On 26 June 2015 at 21:14, Andrzej Krzemie=C5=84ski = wrote: >> >> > The main criticism of this proposal was that it affects the optional's >> > semantics: >> > >> > optional od {2.3}; >> > double d =3D compute_val(); >> > >> > assert (od); // contains value >> > *od =3D d; >> > assert (od); // contains value? >> > >> > The second assertion always holds in normal optional. In the "optimize= d" >> > version, it depends on the value of d. >> >> I have used an 'optimised optional' of the type suggested in this >> paper for years. At some point I decided to forbid this case -- a user >> should be completely unable to tell any space optimisation is being >> performed (except the object is smaller obviously). That does mean you >> can't compress types such as int or double. >> >> Chris > > > In what cases *can* you compress then? Any type where at least one bit pattern isn't used in a valid object. Personally, I mainly compress containers (std::vector, std::list, std::map, etc.). I know on any system I care about malloc is never going to return (void*)1, so any object which contains a pointer can assign that value to a pointer to represent disengaged. Chris --=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/. .