CGAL users discussion list

["S. Gerace" <>]

Greetings, 

Sorry if this is a double post, I tried to send this earlier before
subscribing to the mailing this and although I could see it in Nabble, the
mailing this seemed to reject my post.

I'm having a problem with the newest version of CGAL and trying to utilize
some of the template functions within the geometric kernels. Basically, I
have a few classes that inherit from CGAL objects (Segment_2, Vector_2,
etc.) that add convenience functions to these classes for my particular
application. Previously (CGAL 3.5.1) this was not an issue and everything
compiled fine; yesterday I compiled CGAL 3.7 and I got a bunch of compiler
errors yelling about a "conversion from CGAL::Null_tag to non-scalar type
CGAL::Object". I've been able to isolate the issue in the following simple
example: 
// This class just inherits from CGAL Segment_2
class Segment_2D : public CGAL::Segment_2
{
public:

    // Constructs a new Segment2D with a given start and end coordinates
    inline Segment_2D(const CGAL::Point_2 &p,
                      const CGAL::Point_2 &q)
        : CGAL::Segment_2(p, q) { }
};

void CgalInheritanceTest()
{
    typedef CGAL::Exact_predicates_inexact_constructions_kernel K;

    // Using CGAL classes with CGAL::intersection works fine
    CGAL::Segment_2 s1(CGAL::Point_2(0,0), CGAL::Point_2(1,1));
    CGAL::Segment_2 s2(CGAL::Point_2(0,0.5), CGAL::Point_2(1,0.5));
    bool doesIntersect = CGAL::do_intersect(s1, s2);
    CGAL::Object result = CGAL::intersection(s1, s2);

    std::cout << "Did intersect: " << doesIntersect << std::endl;
    std::cout <<   "Found intersection: " << !(result.is_empty()) <<
std::endl << std::endl;


    // Using child classes of CGAL classes with CGAL::intersection does not
work
    Segment_2D sg1(CGAL::Point_2(0,0), CGAL::Point_2(1,1));
    Segment_2D sg2(CGAL::Point_2(0,0.5), CGAL::Point_2(1,0.5));

    bool doesIntersect2 = CGAL::do_intersect(sg1, sg2); // This call works
fine
    CGAL::Object result2 = CGAL::intersection(sg1, sg2); // Compile error:
conversion from CGAL::Null_tag to non-scalar type CGAL::Object with CGAL 3.7

    std::cout << "Did intersect: " << doesIntersect2 << std::endl;
    std::cout <<   "Found intersection: " << !(result2.is_empty()) <<
std::endl;
}

This code compiles and runs without issues with CGAL 3.5.1, but has an issue
with CGAL 3.7...both were compiled on Windows 7 using MinGW/GCC 4.4.0. Any
help would be greatly appreciated. 

Thanks, 

Sal

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