From -3944581726493864738 X-Google-Thread: f78e5,4176870a6d7b2d6 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news1.google.com!news.glorb.com!news.zanker.org!news.clara.net!wagner.news.clara.net!peer-uk.news.demon.net!kibo.news.demon.net!news.demon.co.uk!demon!stump.algebra.com!devnull From: ben-public-nospam@decadentplace.org.uk (Ben Hutchings) Newsgroups: comp.std.c++ Subject: Re: Union fun Date: Tue, 19 Oct 2004 14:47:10 GMT Lines: 43 Sender: mail2news@demon.net Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: References: NNTP-Posting-Host: news.news.demon.net X-Trace: news.demon.co.uk 1098197237 2282 158.152.254.254 (19 Oct 2004 14:47:17 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Tue, 19 Oct 2004 14:47:17 +0000 (UTC) X-Received-SPF: Received-SPF: none (mailbox10.ucsd.edu: domain of mod-submit@uni-berlin.de does not designate permitted sender hosts) X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-User-Agent: slrn/0.9.7.4 (Linux) X-Spam-Checker-Version: SpamAssassin 2.64-mulga_r1 (2004-01-11) on mulga.cs.mu.OZ.AU X-Orig-X-Trace: news.uni-berlin.de HQ2huDmtet2RYdtal6IOYwHio4DcUvKRTk6gtqoZqV6MxRjqc= X-Spam-Status: No, hits=-4.9 required=5.0 tests=AWL,BAYES_00 autolearn=ham version=2.64-mulga_r1 X-Reply-To: Ben Hutchings X-Received: (from fjh@localhost) by mulga.cs.mu.OZ.AU (8.12.10+Sun/8.12.9/Submit) id i9JElAPg015739; Wed, 20 Oct 2004 00:47:10 +1000 (EST) X-Path: comp-std-cpp-robomod!not-for-mail X-Spam-Level: X-Delivered-To: std-c++@ucar.edu X-Spamscanner: mailbox10.ucsd.edu (v1.5 Aug 25 2004 09:28:35, -2.8/5.0 3.0.0) X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f X-Orig-Path: decadentplace.org.uk!nobody X-Newsgroups: comp.std.c++ X-MailScanner: PASSED (v1.2.8 78304 i9J90Hop078516 mailbox10.ucsd.edu) Xref: g2news1.google.com comp.std.c++:3112 "John Max Skaller" wrote: > On Mon, 18 Oct 2004 11:35:01 -0600, Ben Hutchings wrote: > >> "John Max Skaller" wrote: > >>> union U2 { int b; float a; U1() : a(1.0), b(1); } y; >>> y.a; // 1.0f, well defined > >> The standard says in 12.6.2/3: >> >> "If a ctor-initializer specifies more than one mem-initializer for >> the same member, for the same base class or for multiple members >> of the same union (including members of anonymous unions), the >> ctor-initializer is ill-formed." > > Ah, thanks. Pity you can put non-POD types in unions then, > I need to do that.. is there a proposal for a template like > > store_of > > which has the alignment and size of T and which can be > used in a union, for all value types T? No, but the Type Traits part of TR1 includes information about the required alignments (std::tr1::alignment_of). > If I had one of those, it might do as a poor man's > replacement for unions of arbitrary types, the lack of which is > a fairly serious defect. Boost.Variant can do that for you. -- Ben Hutchings The world is coming to an end. Please log off. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ]