Re: [Swig-user] Downcasting in Python wrappers?

[Nitro <ni...@dr...>]

Am 12.07.2008, 13:44 Uhr, schrieb Kai Sterker <kai...@gm...>:

> I'm using SWIG to generate Python wrappers and have run into the
> following issue.
>
> I have a C++ base class and derived from that several other classes,
> each with its own distinct set of methods. Another class stores
> instances of the derived classes and has a method get_base() that
> returns a specific instance.
>
> Now, on Python side, I am getting a base instance by calling
> get_base(), but would like to use it to invoke methods of derived_a.
> However, I see now way to cast the base instance into a derived_a
> instance.
>
> What I did as a workaround is adding the following to my interface file:
>
> %extend xyz {
>     derived_a* get_derived_a (const std::string & name)
>     {
>         return dynamic_cast<derived_a*> (self->get_base (name));
>     }
> };
>
> However, I would have to do that for every derived_<x> which is not
> very elegant.
>
> Does SWIG provide a better way to handle something like this?

There's the swig/lib/typemaps/factory.swg file which does more or less  
what you suggest. To use it write %include factory.i .

-Matthias