Re: c++/7780: -Woverloaded-virtual generating false-positives

[Wolfgang Bangerth <bangerth at ticam dot utexas dot edu>]

> >     I think the example you give should indeed give a warning:
> >     ----------------------
> >     class A
> >     {
> >       public:
> >         virtual int ThisFunctionShouldNotCauseAHidingWarning(char*);
> >         virtual int ThisFunctionShouldNotCauseAHidingWarning(char*,int);
> >     };
> >     
> >     class B : public A
> >     {
> >       public:
> >         virtual int ThisFunctionShouldNotCauseAHidingWarning(char*,int);
> >     };
> >     
> >     int main()
> >     {
> >       return 0;
> >     }
> >     -----------------------------------------
> 
> As I understood it, this warning was to alert the programmer when they
> overload a (hopefully virutal) function that they intended to override.
> 
> I am thinking of examples like:
> class A
> {
>   public:
>     virtual int ThisFunctionShouldCauseAHidingWarning(int);
> };
> 
> class B : public A
> {
>   public:
>   virtual int ThisFunctionShouldCauseAHidingWarning(long);
> };
> 
> If this was not the intent of this warning, perhaps another warning
> should catch this case.

No, this is particularly the case the warning was for. In this case you 
are right.

However, the fact that in _my_ example the warning is triggered is that 
overloading the function in B also hides the other function with the 
different numbers of parameters. You'll see this if in my example you 
replace main with this:
  int main() 
  {
    B b;
    b.ThisFunctionShouldNotCauseAHidingWarning('c');
  }
One would think that this calls the single parameter function of the base 
class, but in fact the two-parameter function in the derived class also 
hides the single-parameter function! So, even without 
-Woverloaded-virtual, you'll get an _error_, not a _warning_. The warning
is there to warn you about this fact even if you do not attempt to 
actually call the function.

Does this clarify the usefulness of the warning somehow?

Regards
  Wolfgang


-------------------------------------------------------------------------
Wolfgang Bangerth              email:           bangerth@ticam.utexas.edu
                               www: http://www.ticam.utexas.edu/~bangerth