Re: [Swig-user] C++ Inheritance

[Charlie S. <cf...@in...>]

Thanks Marcelo,

Very helpful. 

Makes me wonder if there could be a more elegant way?  Maybe a template 
method on the Geometry class, so at least the downcast method only has 
to be written once?

Are there any plans to have SWIG generate this sort of code - at least 
the downcast method/s ?

Thanks,

Charlie



Marcelo Matus wrote:
> you need to add the dynamic cast operations for all the Geometry object
>
> %extend Circle {
>   static Circle *dcast(Geometry *g) { return dynamic_cast<Circle *>(g); }
> }
>
> %extend Point {
>    static Point *dcast(Geometry *g) { return dynamic_cast<Point *>(g); }
> }
>
> ....
>
> then use the infamous 'switch' operation, but implemented in Ruby 
> (here in pseudo C/Python):
>
> def  unpackGeometry(geom_string):
>        geom = GeomFactory.new.parseGeometry(geom_string)
>        circle = GeomFactory.Circle.dcast(geom)
>        if (circle != Qnil) return circle
>        point = GeomFactory.Point.dcast(geom)
>        if (point != Qnil) return point
>        ....
>        return Qnil
>
>
> and use it as
>
>  obj = unpackGeometry(geom_string)
>
> then 'obj' will be what you expect, ie, a circle, or a point, etc.
>
> And of course, that is assuming Geometry has a virtual member/descructor.
>
> class Geometry {
> public:
>   virtual ~Geometry() {}
> }
>
>
> Marcelo
>
>
> Charlie Savage wrote:
>
>> Hi everyone,
>>
>> Was wondering what the best way to handle this issue with C++ 
>> inheritance (seem like an obvious question, but didn't dig anything 
>> up with Google or the mailing list):
>>
>> class GeomFactory {
>>    Geometry* parseGeometry(char* geom_serialized_to_string) {}
>> }
>>
>> class Geometry {
>>    Geometry() {}
>> }
>>
>> class Point: public Geometry {
>>    Point() {}
>> }
>>
>> class Line: public Geometry {
>>    Line() {}
>> }
>>
>> Etc...including polygon, multipoint, multipolygon, geometry 
>> collection, etc.
>>
>> So from Ruby:
>>
>> geom_string = '<serialized form of geometry>'
>> geom = GeomFactory.new.parseGeometry(geom_string)
>>
>> The class of geom will always be geom, not point, not line, not 
>> polygon.  Of course, the underlying C++ object is really a point, 
>> line, etc. so the wrapper Ruby object is incorrect.
>> How do I get the correct Ruby wrapper object - i.e., a Ruby point for 
>> a C++ point, a Ruby line for a C++ line, etc.
>>
>> Charlie
>>
>>
>>
>>
>>
>>
>>
>>
>> Question about C++ inheritance (I'm running into an issue with C++ 
>> inheritance and haven't managed to find anWas wondering if 
>> any...@li...
>
>
>
>