Path: utzoo!attcan!uunet!decwrl!petunia!news
From: jdunn@polyslo.CalPoly.EDU (Drunk Dude #3)
Newsgroups: comp.lang.c++
Subject: Re: Multiple inheritance and type casting
Message-ID: <2709eabf.5abd@petunia.CalPoly.EDU>
Date: 3 Oct 90 13:42:23 GMT
References: <5087@uqcspe.cs.uq.oz.au>
Organization: The Consistently Drunk Dudes of Spike's
Lines: 45



In article <5087@uqcspe.cs.uq.oz.au> iain@batserver.cs.uq.oz.au writes:
>
>Assume the following class definitions:
> [...]
>
>If D1::f() cast the formal parameter to type D1 (ie. (D1 &) b), for
>example to interrogate private data members, no problems. However, if
>X::f() casts to an X& my compiler complains (TC++ V1.0) saying
>"Cannot cast from B& to X&".

This works for me:

void X::f(X &x) {}     // standard method def

X x;
Y y;  // Y is derived from X

X.f(*(X *)&y);         // get a pointer and convert the pointer

This actually makes sense, because converting from one object to another
requires a new (anonymous) object to be created, and that requires that
a constructor exist on the casted-to type to do the conversion.

I have found one bug in TC++ 1.0 involving multiple inheritance, and I 
believe I am in the process of tracking another down now.  If you want
me to send you a copy of the compiler-breaking code when I send it off
to Borland, let me know.  Probably be a week before I get around to it,
though...

>+----------------------------------------------------------------------+
>+ Dr Iain Fogg                                                         +
>+----------------------------------------------------------------------+

-jd




-- 
Major@Jungle1        Plans to go with the flow have the one flaw of being plans 


jdunn@polyslo.CalPoly.EDU