CGAL users discussion list

[Cody Rose <>]

On 1/30/2013 2:48 AM, Philipp Moeller wrote:
> "Sebastien Loriot (GeometryFactory)" 
> <>
>  writes:
>
> > On 01/30/2013 11:39 AM, Philipp Moeller wrote:
> > > Cody 
> > > Rose<>
> > >   writes:
> > >
> > > > Hello,
> > > >
> > > > With CGAL 4.1 I am unable to use the Nef_polyhedron_3 package with
> > > > BOOST_RESULT_OF_USE_DECLTYPE defined. I am using:
> > > You have to define BOOST_RESULT_OF_USE_DECLTYPE because your compiler
> > > does not implement a fully conforming decltype. (AFAIK, the only
> > > compiler that currently does is clang 3.2).
> > I guess you meant you can't define BOOST_RESULT_OF_USE_DECLTYPE ?
> You can define it yourself, it is just not guaranteed to work for every
> library (as you can see here). This was even one of the fixes for using
> Boost.Range with lambdas.

Yes, this is exactly what I was trying to do, as I demonstrated: get 
parts of Boost.Range to work with lambdas in MSVC 2010. That kind of 
thing is what the macro is for.

> > > > CGAL 4.1
> > > > the CORE numeric library, along with its dependencies (GMP etc)
> > > > Boost 1.47
> > > > Visual Studio 2010
> > > >
> > > > The problem does *not* appear in CGAL 3.9.
> > > CGAL 3.9 didn't use result_of. That's why you don't see the problem.
> > >
> > > > The following code reproduces the problem for me:
> > > >
> > > > // This is the problematic define.
> > > > #define BOOST_RESULT_OF_USE_DECLTYPE
> > > >
> > > > #include<vector>
> > > >
> > > > #include<boost/range/algorithm.hpp>
> > > > #include<boost/range/adaptors.hpp>
> > > >
> > > > #include<CGAL/Cartesian.h>
> > > > #include<CGAL/CORE_Expr.h>
> > > > #include<CGAL/Nef_polyhedron_3.h>
> > > >
> > > > typedef CORE::Expr                        NT;
> > > > typedef CGAL::Cartesian<NT>                 K;
> > > > typedef CGAL::Nef_polyhedron_3<K>         nef_polyhedron_3;
> > > >
> > > > int main() {
> > > >       std::vector<int>  a(0, 3);
> > > >       a[0] = 1;
> > > >       a[1] = 2;
> > > >       a[3] = 3;
> > > >       std::vector<int>  b;
> > > >
> > > >       // With BOOST_RESULT_OF_USE_DECLTYPE defined, the following line
> > > > causes an error.
> > > >       nef_polyhedron_3 foo;
> > > This is because MSVC decltype triggers instantiation prematurely.
> > >
> > > >       // Without BOOST_RESULT_OF_USE_DECLTYPE defined, the following
> > > > line causes an error.
> > > This is because built-in lambdas require a decltype based result_of.
> > >
> > > >       boost::copy(a | boost::adaptors::transformed([](int x) { return x
> > > > * 2; }), std::back_inserter(b)); return 0; }
> > > It would be nice if both worked together, even with a broken
> > > decltype. If I remember correctly there was a work-around involving two
> > > Type_equality_wrappers when instantiating kernels.
Yeah, I was hoping there would be a workaround either for my code or 
maybe even put into CGAL at some point. I can totally understand not 
wanting to work around a weird corner-case bug in a compiler that isn't 
even the latest version, though. Oh well! All it seems to really be 
affecting is boost::adaptors::transformed.

Thanks,
Cody