CGAL Bug or GCC6 Compiler Bug ?

[afabri]

Issue Details

Error message in a master branch testsuite

Environment

• Operating system (Windows/Mac/Linux, 32/64 bits):
• Compiler:
• Release or debug mode:
• Specific flags used (if any):
• CGAL version: CGAL-6.1-I-95, that is github master branch
• Boost version:
• Other libraries versions if used (Eigen, TBB, etc.):

[afabri]

What happens is that this overload of convex_hull_3() should be picked, but it isn't,
Instead this overload is picked.

[lrineau]

That is a CGAL bug. The call is:

  typedef  std::vector<Point_3> Vertices;
  typedef std::vector<std::array<int,3> > Faces;

  Vertices vertices;
  Faces faces;

  std::vector<Point_3> points;
  // [...]
  CGAL::convex_hull_3(points.begin(), points.end(), vertices, faces);

There are two possible matches:

• cgal/Convex_hull_3/include/CGAL/convex_hull_3.h

  Lines 993 to 996 in 299a89f

  	template <class InputIterator, class PolygonMesh, class Traits>
  	void convex_hull_3(InputIterator first, InputIterator beyond,
  	PolygonMesh& polyhedron,
  	const Traits& traits)

• cgal/Convex_hull_3/include/CGAL/convex_hull_3.h

  Lines 1082 to 1088 in 299a89f

  	template <class InputIterator, class PointRange, class TriangleRange>
  	void convex_hull_3(InputIterator first, InputIterator beyond,
  	PointRange& vertices,
  	TriangleRange& faces,
  	std::enable_if_t<CGAL::is_iterator<InputIterator>::value>* = 0,
  	std::enable_if_t<boost::has_range_iterator<PointRange>::value>* = 0,
  	std::enable_if_t<boost::has_range_iterator<TriangleRange>::value>* = 0)

And none of them is rejected by the std::enable_if_t.

[afabri]

Well, all other compilers succeed. Do you have an idea for a fix @lrineau ?

[sloriot]

I tried to reproduce it with gcc master but it could not. I would suggest to remove the traits and introduce a named parameter (the PolygonMesh parameter is anyway missing the VPM parameter).

[afabri]

How can it make a difference when you replace \tparam Traits with \tpram NamedParameters?

[MaelRL]

How can it make a difference when you replace \tparam Traits with \tpram NamedParameters?

You can use the macros CGAL_NP_TEMPLATE_PARAMETERS and CGAL_NP_CLASS (https://github.com/CGAL/cgal/blob/master/STL_Extension/include/CGAL/Named_function_parameters.h) instead of a generic template parameter called NamedParameters to avoid ambiguity.