From -5786681545251443064 X-Google-Thread: 7894ca11fe,dcc43f3425b0e139 X-Google-Attributes: gid7894ca11fe,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news2.google.com!npeer02.iad.highwinds-media.com!news.highwinds-media.com!feed-me.highwinds-media.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Sun, 20 Sep 2009 10:20:02 -0500 Return-Path: To: (Usenet) From: "Bo Persson" Newsgroups: comp.std.c++ Subject: Re: Immutability of set elements Organization: unknown Sender: cppmods@cs.rpi.edu Approved: stephen.clamage@sun.com Message-ID: <7hmbfoF2uc89oU1@mid.individual.net> References: <7.0.0.16.2.20090919120102.05e1e878@aristeia.com> X-Original-Date: Sun, 20 Sep 2009 11:38:10 +0200 X-Submission-Address: std-c++@netlab.cs.rpi.edu Date: Sun, 20 Sep 2009 10:14:24 CST Lines: 40 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-wmRxWnlVbsTo0VAbMCoqN/Ds+2pBgqhzinPzJy55MfugI5qarelnqEvcQCEvGW68ejZwULM4THpncyZ!1KwmCyetDYshlrRk4T6i7wY8LzK8+kw5Y63x2zuvTdEKcBjkaa5wJT52X2AkyA== X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Xref: g2news2.google.com comp.std.c++:1378 Scott Meyers wrote: > >> If users need to modify elements, it is possible to use mutable >> members or const_cast. > > So here's my question: what does it mean for a set key to be > immutable? The commentary on issue 103 suggests that modifying such > keys via mutable members or a const_cast is okay, but presumably > doing > so in such a way that would affect the sortedness of the container > is > not okay. Does modifying a set key lead to undefined behavior? If > so, in all cases, or only under some conditions, e.g., when the > sortedness of the container is affected? > From what I understand, some people would like to have the possibility of updating parts of the stored data, that is not actually part of the key. With a user supplied comparison-functor, parts of a stored structure might have no effect on the ordering. For example, you might have an existing data structure that already contains the key value. Ordinarily you would store this in a map, but to avoid storing the key twice, you use a set with a special comparator. Anyone actually doing this, is supposedly skilled enough to use a proper const_cast when updating the non-key data. :-) Bo Persson -- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@netlab.cs.rpi.edu] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ]