CGAL users discussion list

[Philipp Moeller <>]

"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.

>
>>
>>>
>>>
>>> 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.