🚀 go-pugleaf

john (j.d.) hickin (hickin@bnr.ca) wrote:

|> Now that the standard has carefully specified what virtual functions run when
|> called from constructors/destructors in objects with multiple inheritance it
|> becomes possible to allow the following:

|> 	class X { public: X(); virtual ~X() = 0; };

|> Has this been considered?

In what way?  This has always been legal, and I see nothing in the
present draft to change it.  I occasionally use the idiom to force a
class to be abstract even when I want to provide default behavior for
all of the member functions.

Of course, you do still have to provide an implementation of the
destructor somewhere.
-- 
James Kanze           (+33) 88 14 49 00          email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
Conseils, études et réalisations en logiciel orienté objet --
              -- A la recherche d'une activité dans une region francophone

---
[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
  is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]

In message <47voa1$969@gabi.gabi-soft.fr> - kanze@gabi-soft.fr (J. Kanze) 
writes:
:>
:>
:>john (j.d.) hickin (hickin@bnr.ca) wrote:
:>
:>|> 	class X { public: X(); virtual ~X() = 0; };
:>
:>|> Has this been considered?
:>
:>In what way?  This has always been legal, and I see nothing in the
:>present draft to change it.  I occasionally use the idiom to force a
:>class to be abstract even when I want to provide default behavior for
:>all of the member functions.
Yes, but there is a difference between a normal member function and a dtor. 
The normal memberfunction has to be called explicitly before it is invoked. 
If the function is overridden, it is not called unless you explicitly call it 
from the overridden version. Doing this will generate an error since their 
actually is no implementation for the function called. With dtors, this is 
different as all inherited dtors are automatically called when an object is 
destructed. What you are saying here is that there is somewhere in the draft 
a rule which states that if a dtor is declared pure virtual, a default 
implementation (or none at all) is automatically created. Is this the case ?

Wim Veldhuis,
veldhuis@xs4all.nl
---
[ 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 
]