From 3025749931901575917 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,f5d433881cc29cff X-Google-Attributes: gidf78e5,public From: Jason Merrill Subject: Re: Named return value optimisation- reprise. Date: 1997/06/20 Message-ID: #1/1 X-Deja-AN: 251293625 References: <33a345bf.7425526@news.ipswich.gil.com.au> <33A478C1.329@acm.org> <33a5f9a1.5157214@news.ipswich.gil.com.au> X-Original-Date: 19 Jun 1997 16:06:11 -0700 Organization: Cygnus Solutions, Sunnyvale, CA X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUBM6pBjOEDnX0m9pzZAQG99QF/Y+LH1vMklmQskRpkVigC4jW9AMD/XZiN fZnrrjk9wmsni/dO7GGa1JD/QceN+Md0 =NrjU Newsgroups: comp.std.c++ Originator: fjh@mundook.cs.mu.OZ.AU >>>>> James Kanze writes: > Jason Merrill writes: >> 15Whenever an automatic (_basic.stc.auto_) class object is copied and >> the original object and the copy have the same type, and the block >> containing the original object exits (_stmt.jump_) immediately after >> the copy is created, an implementation is permitted to treat the >> original and the copy as two different ways of referring to the same >> object and not perform a copy at all. In that case, the object is >> destroyed when the copy would have been destroyed without the >> optimization. >> >> I think this only allows the RVO. > It may not even allow that, if the function has local variables. There > may be calls to other destructors between the moment the return value is > copied and the destructor of the object being copied. That's why I said "block exits" rather than "object is destroyed". Jason --- [ 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 ] [ FAQ: http://reality.sgi.com/employees/austern_mti/std-c++/faq.html ] [ Policy: http://reality.sgi.com/employees/austern_mti/std-c++/policy.html ] [ Comments? mailto:std-c++-request@ncar.ucar.edu ]