CGAL users discussion list

[Ben Supnik <>]

Hi,

When you sub-class a CGAL type you may have to "copy out" to the 
sub-class two possible sets of stuff:

1. type-defs...because the template typedefs work off a specific 
typename and do not know about inheritance.  So whatever types are 
declared inside Polgon_2, you need to "map".

Example I did with GPS2:

class   Polygon_set_2   : public CGAL::General_polygon_set_2<Traits_2, Dcel > 
{
public:

typedef CGAL::General_polygon_set_2<Traits_2, Dcel >      base;
typedef base::Traits_2                          Traits_2;
typedef base::Dcel                              Dcel;
typedef base::Polygon_2                         Polygon_2;
typedef base::Polygon_with_holes_2              Polygon_with_holes_2;
typedef base::Arrangement_2                     Arrangement_2;
typedef std::size_t                             Size;

You may also have to wrap the constructors...C++ won't write a ctor 
taking type X automatically just because your base class has one.

cheers
Ben


 wrote:
> Hello,
>
> Beware : I might be a silly question !
>
> To be able to add some functionalities (like void draw()  or void setName) to
> Polygon_2 class, I'm looking for the way to inherit from the class.
>
> To aim that I did the following declaration for my new class :
>
> ...
>
> #include <CGAL/Polygon_2.h>
> #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
>
> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
> typedef K::Point_2 Point;
> typedef CGAL::Polygon_2<K> Polygon_2;
>
> class AC_Polygon : public CGAL::Polygon_2<Polygon_2>
> {
> public:
>        AC_Polygon();
>     ~AC_Polygon();
>
>     void draw() const;
> };
>
> ...
>
> It compiles well, but when I instantiate my new class AC_Polygon,
> I do not have the methods like :
>
> is_simple()
>
> is_convex()
>
> the compiler says :
>
> /usr/include/CGAL/Polygon_2/Polygon_2_simplicity.h:135: erreur: no type named
> «Orientation_2» in «class
> CGAL::Polygon_2<CGAL::Filtered_kernel<CGAL::Simple_cartesian<double> >,
> std::vector<CGAL::Point_2<CGAL::Filtered_kernel<CGAL::Simple_cartesian<double>
> > > ,
> std::allocator<CGAL::Point_2<CGAL::Filtered_kernel<CGAL::Simple_cartesian<double>
> > > > > > »
>
>
> Any ideas
>
> Gilles-- 
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