From 8750776033764020214 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,ede379f5dbbc1549 X-Google-Attributes: gidf78e5,public From: Christopher Eltschka Subject: Re: Suggestion: "typeof" keyword Date: 1999/08/25 Message-ID: <37C3DA57.25C88799@physik.tu-muenchen.de>#1/1 X-Deja-AN: 517138796 Content-Transfer-Encoding: 7bit Approved: Fergus Henderson References: <7nt3vl$1oe$1@nnrp1.deja.com> <7oh7o8$t3f$1@nnrp1.deja.com> <7ol6hi$ej9$2@news.BelWue.DE> <120819991357412479%lisa_lippincott@advisories.com> <37BBDDCA.90D590D4@physik.tu-muenchen.de> X-Original-Date: Wed, 25 Aug 1999 13:58:15 +0200 X-Accept-Language: German/Germany, de-DE, German, de, en Content-Type: text/plain; charset=us-ascii X-Complaints-To: news@news.unimelb.edu.au X-Trace: izvestia.its.unimelb.edu.au 935608601 1390 128.250.29.17 (25 Aug 1999 19:16:41 GMT) Organization: [posted via] Leibniz-Rechenzentrum, Muenchen (Germany) X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUAN8RA8+EDnX0m9pzZAQF5bwF+LU0rgDJ5RcXzbh0T4zVnDDnCmLiRqknz 0NXnPiDXibGcIsEMhQ83uKSU3ooj4Mpt =gImD Mime-Version: 1.0 NNTP-Posting-Date: 25 Aug 1999 19:16:41 GMT Newsgroups: comp.std.c++ "Siemel B. Naran" wrote: > > On 19 Aug 1999 16:39:34 GMT, Christopher Eltschka > >"Siemel B. Naran" wrote: > > >> In one of my posts I used this > >> typeof(A*B+C) MultiplyAdd(...) { ... } > > >That's problematic: > > > >class X {}; > >class Y { Y operator*(); }; > >X operator*(X, Y); > >Y operator*(X*, Y); > > > >typeof(X**Y) a > > The notation "X*" to mean pointer to an 'X' is wrong. According to the current rules of writing types, writing "X*" to mean "pointer to X" is right. > One should say > "&X" to get a pointer to an 'X'. This may not work if X has overloaded operator& to return something different than X* (sic!) > To summarize, "&X" means operator& > applied to an X object -- in short, X::operator&. An "*Y" means > operator* applied to a Y object -- in short, Y::operator*. So the > meaning is unamgiguous: typeof(X**Y) is simply X. You added a new rule on the fly to make it unambiguous. The new rule is "you may not use any type that is not given by a single name". Now if you should need such a type, you must either name if (with an earlier typedef), or find an expression which resolves to that type (your &X). It's a rule that doesn't fit nicely into C++, where you can use the full type notation everywhere you need a type. A better way would be to make a special syntax for "arbitrary object of type X", like [X]. Then the example above would either read typeof([X]**[Y]) where both * are operators, or typeof([X*]*[Y]) where the first * is part of the type X*. However, if you replace the syntax [X] by obj(), you can do it even without an additional extension, by just declaring template T obj(); --- [ 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://reality.sgi.com/austern_mti/std-c++/faq.html ]