CGAL users discussion list

[Marc Glisse <>]

On Fri, 7 Aug 2015, Martin Seemann wrote:

> I recently came across a regression, which is demonstrated by the example 
> below:
>
> #include <CGAL/Simple_cartesian.h>
> int main() {
>         typedef CGAL::Simple_cartesian<double> K;
> 	CGAL::Line_3<K> line(CGAL::Point_3<K>(0, 0, 0), CGAL::Point_3<K>(1, 
> 1, 1));
>         std::cout << line.point(0) << std::endl;
> 	return 0; 
> }
>
> Using GCC 5.2.0 (Archlinux), the above example compiles fine with -std=c++11 
> but when switching to -std=c++14, the compiler starts complaining about 
> ambiguous 'get(...)' overloads in CGAL/Cartesian/Line_3.h:78.
> I figured that it was caused by some c++14 additions to the standard library 
> (http://en.cppreference.com/w/cpp/utility/pair/get, overloads 4-7).
> A quick fix is to make the desired namespace explicit in 
> CGAL/Cartesian/Line_3.h, i. e. to replace lines 78 and 83 by
>    return CGAL::get(base).first;
> and
>    return CGAL::get(base).second;
> respectively.
> After these modifications, the above example (and also my real project) 
> compiles fine.

https://github.com/CGAL/cgal/commit/b7f98495991ee49b2b01e64a36bb3b5c1e89a615

> However, prefixing with CGAL:: in this place seems strange to me, since we 
> are already in namespace CGAL. Furthermore, I do not understand why the 
> std::get variants even participate in overload resolution, given that they 
> are defined in std (I couldn't find any dangerous
> 'using namespace std' anywhere in the CGAL code base either).
>
> Maybe someone with a deeper understanding of the language can give his 
> opinion if this situation should be corrected in CGAL or in the standard 
> library.
> BTW: The error also happens with clang (v3.6.2)
> (My CGAL version is 4.6.2)

ADL means that if the arguments involve a type defined in namespace std 
(even indirectly), std::get gets to participate.

--
Marc Glisse