From -1063365396674196045 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fc772,b03957313f1e9325 X-Google-Attributes: gidfc772,public X-Google-Thread: f78e5,b03957313f1e9325 X-Google-Attributes: gidf78e5,public From: Hyman Rosen Subject: Re: my own 'pointer type' Date: 1997/03/07 Message-ID: <5fokhq$j74@netlab.cs.rpi.edu>#1/1 X-Deja-AN: 223734269 Sender: cppmods@netlab.cs.rpi.edu References: <5fjlv7$jjl@netlab.cs.rpi.edu> X-Submission-Address: c++-submit@netlab.cs.rpi.edu X-Original-Date: Thu, 6 Mar 1997 15:38:00 GMT Organization: JYACC, Inc. Newsgroups: comp.lang.c++.moderated,comp.std.c++ "Enno Rehling" writes: > Here's what I want to do: I want a kind of 'pointer type' that would allow > me to have something like a pointer to an object, plus additional info (an > id, for example). I figured that templates would be neat, I'd write ptr > a; and be able to access a.id, and overload the -> operator to access the > contents of A. Worked fine, up to a point: typecasts. > At one point, I had a class B derived from A, and it dawned on me that > ptr does not conform to ptr, because it's not derived from it. There's a better way than the one you used, but it requires support for member templates: template struct ptr { int id; T *p; ptr(int ID, T *P) : id(ID), p(P) { } template operator ptr() { return ptr(id, p); } }; Note the templated typecast member function - it will succeed only for those cases where a U* can be initialized from a T*, which will give you exactly the behavior you want. Now all you need to do is find a compiler which supports this. [ Send an empty e-mail to c++-help@netlab.cs.rpi.edu for info ] [ about comp.lang.c++.moderated. First time posters: do this! ]