Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!husc6!ukma!tut.cis.ohio-state.edu!ucbvax!agate!saturn!daniel
From: daniel@saturn.ucsc.edu (Daniel Edelson)
Newsgroups: comp.lang.c++
Subject: multiple inheritance
Keywords: nits, multiple inheritance
Message-ID: <7105@saturn.ucsc.edu>
Date: 12 May 89 21:44:32 GMT
References: <203@riunite.ACA.MCC.COM> <1527@cod.NOSC.MIL> <14133@paris.ics.uci.edu>
Reply-To: daniel@saturn.ucsc.edu (Daniel Edelson)
Organization: Univ of Calif, Santa Cruz; Computer & Info Sci
Lines: 59

++ my comments -- daniel

Within <14133@paris.ics.uci.edu> Doug Schmidt <schmidt@siam.ics.uci.edu> asks:

>Here's a quick nit.  Is the following a legal use of multiple inheritance?  

++ I believe not.

>              As you can see, from one direction class a's member
>function `int foo ()' is private for all classes derived from class b.
>However, on another path it is public.  In class d's constructor,
>where `foo ()' is called, foo appears to be derived from classes where
>it is both private and public.

++ Private is private, is it not? If the field is private in a base class
++ then it is not available outside of member functions of that class.
++ Your question applys if you use protected instead of private.

>Which visibility status prevails?  Is this ambiguous, legal, or illegal?
>thanks, Doug

>  class a {
>  public:
>    int foo () { printf ("foo\n"); }
>  };

++ I changed ``private'' to ``protected'' in classes b and d

>  class b : public a {
>  protected:
>    a::foo; // made protected for all classes derived from class b.
>  };
  
>  class c : public a {
>  public:
>    c () {printf ("c\n");}
>  };
  
>  class d : public c, public b {
>  public:
>                    // both public *and* private!! which prevails?
>    d () { printf ("d\n"); foo (); } 
>  };

++ My understanding is that if the call is ambiguous it's a
++ syntax error. That might not apply in this case since this is 
++ the same function being inherited along two different paths of 
++ the DAG. Is this ambiguous, or since it's a single function
++ being referred to twice, is it allowed? If the latter, what
++ happens when it is made virtual? If the former, it can be
++ disambiguated with the :: operator.
  
>| schmidt@ics.uci.edu |

++ Well, I wanted to answer the question but all I've done is
++ ask new ones.

daniel edelson
daniel@saturn.ucsc.edu