[C++-sig] How do I wrap virtual methods

[David Abrahams]

Eric Jardim <ericjardim at gmail.com> writes:

> I saw on the tutorial that you should use a construct like:
>
> struct BaseWrap : Base, wrapper<Base>
> {
>     int f()
>     {
>         if (override f = this->get_override("f"))
>             return f(); // note*
>         return Base::f();
>     }
>
>     int default_f() { return this->Base::f(); }

Does the tutorial really recommend that default_f?  I can't imagine
why.  That's just wrong; you don't need it and it's a bad idea to use
it.  [Joel, can you please fix this ASAP, and the use of default_f
further down?]

> };
>
> // *note: on MSVC use
> //  return call<char const*>(f.ptr());
>
> I think that this will solve the problem, because it tests if there is a 
> overriden method. I am still confused if wrapper<...> will create the 
> apropriate contructors. 

wrappeer<...> doesn't create any constructors by itself.

> So what do "wrapper<..>" really do?

Exactly what's described in
http://www.boost.org/libs/python/doc/v2/wrapper.html#wrapper-spec

> Another thing that I noticed is that I have to reimplement virtual methods 
> on every derived class. This is an accumulative task. Am I right?

I don't know what you mean.

> So, what is the right and safe way to wrap virtual methods?

Everything the tutorial says, aside from the definition and use of
default_f, seems to be right.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com