From -8855385049187183643 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,905ceaebf6c72db5 X-Google-Attributes: gidf78e5,public From: jbuck@Synopsys.COM (Joe Buck) Subject: Re: subscripting: lvalue versus value Date: 1996/06/19 Message-ID: <4q9f09$943@hermes.synopsys.com>#1/1 X-Deja-AN: 161057811 references: <4q3unj$7jj@newsbf02.news.aol.com> x-original-date: 19 Jun 1996 17:56:25 GMT organization: Synopsys Inc., Mountain View, CA 94043-4033 x-auth: PGPMoose V1.1 PGP comp.std.c++ newsgroups: comp.std.c++ originator: austern@isolde.mti.sgi.com mtorhan@aol.com (MTorhan) writes: >If the compiler is aware of the following two versions of the [] >operator... > >Type &operator []( unsigned int ); >Type operator[]( unsigned int ) const; > >...will it choose the 2nd "const" version only when you're working with a >thing that's declared const? Yes, that is what the rules say. >Or, is it smart enuf to use the 2nd "const" >version anywhere the subscripted thing is mentioned, except when the >subscripted thing is at the left of an assignment operator and we need the >1st version for the lvalue. No, it does not do this. operator[] is not treated as special in any way, and also C++ doesn't consider how a result is used when it parses an expression and resolves overloaded operators (other languages, e.g. Ada and VHDL, can do overloading on how a result is used, but not C++). The usual way of proceeding when you require different actions for use as lvalues (e.g. your "array" is a hash table but you only want to create a new entry if it's being used as an lvalue) is to return a "smart reference" object rather than a reference. This is an object of a class that defines a conversion to Type (for accessing as an "rvalue") as well as an assignment operator (for accessing as an lvalue). Discussions on these techniques should be in comp.lang.c++.moderated, I suppose, not here. -- -- Joe Buck (not speaking for Synopsys, Inc) Work for something because it is good, not just because it stands a chance to succeed. -- Vaclav Havel --- [ comp.std.c++ is moderated. To submit articles: Try just posting with your newsreader. If that fails, use mailto:std-c++@ncar.ucar.edu comp.std.c++ FAQ: http://reality.sgi.com/austern/std-c++/faq.html Moderation policy: http://reality.sgi.com/austern/std-c++/policy.html Comments? mailto:std-c++-request@ncar.ucar.edu ]