[C++-sig] Iterators + shared_ptr + Abstract base classes + Pass by reference = help :)

[David Abrahams]

David Sankel <camio at yahoo.com> writes:

> Hello,
>   I have several questions and I think they are all
> most easily answered by example:
>
> class Abstract
> {
> public:
>   shared_ptr<Abstract> clone()=0;
> };
>
> class Filter
> {
> public:
>   vector<shared_ptr<Abstract> >  Abstract data;
>   void doFilter( vector<shared_ptr<Abstract> > &result )=0;
> };
>
> How would I use boost.python to allow python code to
> use Filter as a base class?
>
> I figure there is going to be:
>
> class PythonFilter : public Filter
> {
> public:
>     void doFilter( vector<shared_ptr<Abstract> >& result)
>     {
>         //What goes here?

Here you need to invoke call_method<void>(...) with some argument(s). 
You could write:

    call_method<void>( ref(result) );

But that will only work if you've exposed 

    vector<shared_ptr<Abstract> >

to Python.  My guess is that you haven't.

What type would you like your Python derived class to see when you
override doFilter in Python?

>     }
> }
>
> and:
>
> BOOST_PYTHON_MODULE(embedded_Filter)
> {
>     class_< Abstract > ("Abstract", no_init );
>     class_< Filter,
>             PythonFilter >("Filter")
>     //What goes here?

So far, nothing.  You don't need to (and shouldn't) expose a pure
virtual function to Python.

>     ;
>
> }
>
> The python code to look something like this:
>
> import ...
> class SpecificFilter( Filter ):
>   def doFilter( self, result )
>      #make result some modification of self.data

I don't understand the comment above.


HTH, though.
-- 
                       David Abrahams
   dave at boost-consulting.com * http://www.boost-consulting.com
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