Re: derived class and virtual function
On 18 aug, 03:21, "Alf P. Steinbach /Usenet" <alf.p.steinbach
+use...@gmail.com> wrote:
* =D6=F6 Tiib, on 18.08.2010 02:13:
On 18 aug, 02:54, red floyd<no.spam.h...@its.invalid> wrote:
On 8/17/2010 1:54 AM, James Kanze wrote:
On Aug 13, 10:09 am, "Francesco S. Carta"<entul...@gmail.com> =
wrote:
#include<iostream>
using namespace std;
class Base {
public:
Base(int data = 0) : data(data) {};
Base(const Base& base) : data(base.data) {};
virtual Base* Clone() const {
cout<< "cloning Base"<< endl;
return new Base(*this);
}
int Data() const {
return data;
}
private:
int data;
};
class Derived : private Base {
public:
Derived(int data = 0) : Base(data) {};
Derived(const Derived& derived) : Base(derived=
) {};
Base* Clone() const {
Here, you're still returning a Base. Any conversion takes place
in Derived (where the derivation is visible).
Try changing the return type to Derived*; the compiler should
complain then.
See =A710.3/5 in the standard for details.
James, I thought that the compiler should *not* complain if the
return type of Derived::Clone was Derived*. Isn't that a
covariant return type?
Did you eyeball =A710.3/5? Base is not accessible base class of Derived
so it is not a covariant there by standard.
Base is accessible /in/ D.
That makes the function covariant per =A710.3/5.
Not sure what the discussion otherwise is about, so I can't comment on wh=
at
James meant -- possibly referring to some other invoking code.
Oh yes ... Base is accessible in Derived, since it is its own base
class. My bad, time to go sleep perhaps. <g>
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