Re: Derived class hiding a name
On May 22, 7:57 am, "jord...@gmail.com" <jord...@gmail.com> wrote:
The following code will not compile:
class foo{};
class A{
public:
void f(int a ){a++;};
private:
virtual void f(foo a) = 0;
};
class B : public A{
private:
virtual void f(foo a){};
};
int main(){
B b;
int a=0;
b.f(a);
}
The problem seems to be that all of my functions being named f are
somehow colliding with each other. It seems to me that the
call b.f(a) is unambiguosly pointing to A::f(int), but gcc disagrees.
I can fix this if I namespace the b.f(a) call, but that's a little
ugly. I can also fix it if I put a forwarding function inside B that
calls the proper function inside A, also a little ugly. I could also
mangle my functions' names, but I really feel that's the compiler's
job, not mine, especially since I think I already provided enough
context with a function signature. Also, I'd like to keep the
functions' names as they are, since they reflect an underlying
mathematical structure that really could use the same names.
If a using declaration should be enough to fix this, where should I
place? Or a better fix?
Jordi,
In your main the call to f is unambiguous and resolves to
void B::f(foo), which effectively hides the non-virtual void
A::f(int).
As soon as the compiler sees B::f it stops going up the scope
with the lookup. This could've been fixed by including "using A::f;"
in the public section of B, but that's itself is ambiguous due
to two overloaded members of A.
Solution 0: work against the interface, i.e. through reference
or pointer to A - it works if you replace "b.f(a);" line
with
A& ra(b);
ra.f(a);
Solution 1: name private virtuals differently from public members,
something like Sutter's NVI:
class A
{
public:
void f( int ); // possibly calls virtual do_f
private:
virtual void do_f( const foo& );
};
class B: public A
{
private:
virtual void do_f( const foo& );
};
Hope this helps.
--
Nikolai
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