Re: Inheritance Problem (MSVC 6)
Hans-Dieter Dreier wrote:
----- Original Message -----
From: "Victor Bazarov" <v.Abazarov@comAcast.net>
Newsgroups: comp.lang.c++
Sent: Friday, June 08, 2007 7:35 PM
Subject: Re: Inheritance Problem (MSVC 6)
class b_derived: public a_interface, public a_version_1
I think you meant
class b_derived: public b_interface, public a_version_1
Sure. Sorry for the typo.
What can I do about it, if I need to access a_interface from within
b_interface, other than re-implementing a_version_x in every derived
class?
First of all, your 'a_interface' should probably be derived from
*virtually*. Have you tried that?
Yes. No difference. AFAIK the purpose of virtual inheritance is just
to avoid duplication of data members, so that's no surprise to me.
Do you know how the C++ standard would handle such a situation?
In order to make a class non-abstract all pure virtual functions it
inherits have to have final non-pure overriders. Overriding only
works *directly* in the hierarchy. You cannot expect your class'
uncle to override your class' father's pure functions.
struct ABC {
virtual void foo() = 0;
};
struct CC : ABC {
void foo() {}
};
struct YAABC : ABC {
// here you have one inherited virtual function
// virtual void foo() = 0;
// and it's pure
};
struct MYCC : YAABC, CC {
// here you have two inherited functions, one
// comes from YAABC and its pure and the other
// comes from CC, and it's OK.
};
The language cannot decide for you what MYCC::foo should do. You
actually have two virtual functions inherited, and one of them is
pure that does not have the final overrider. See subclause 10.3
for the actual rules involved. Paragraph 10 shows the situation
similar to yours (no unambiguous final overrider).
To disambiguate the behaviour you have to introduce the final
overrider into 'MYCC'. What it does is up to you, but the most
acceptable way is
struct MYCC : YAABC, CC {
void foo() { return CC::foo(); }
};
That cannot be done automatically, it would generate more problems
than it would solve.
V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask