Re: [Boost-users] [boost-users][Container] Compilation error using new "static_vector".

Subject: Re: [Boost-users] [boost-users][Container] Compilation error using new "static_vector".
From: Krzysztof Czainski (1czajnik_at_[hidden])
Date: 2013-07-19 15:52:06

2013/7/19 Jupp Tscheak <jupp.tscheak_at_[hidden]>

> Hello boost users,
>
Please consider the following example:
>
> [code]
> #include "CGAL/Cartesian.h"
> #include "CGAL/Polygon_2.h"
>
> #include "boost/container/static_vector.hpp"
>
> typedef CGAL::Cartesian<double> Kernel;
> typedef Kernel::Point_2 Point2d;
> typedef CGAL::Polygon_2<Kernel, boost::container::static_vector<Point2d,
> 100> > Polygon2d;
>
> Polygon2d p;
> p = Polygon2d();
> [/code]
>
> Compiling this code snippet with GCC results in following error message:
>
> [error]
> error: no match for 'operator=' in 'p =
> CGAL::Polygon_2<CGAL::Cartesian<double>,
> boost::container::static_vector<CGAL::Point_2<CGAL::Cartesian<double> >,
> 100u> >((*(const Traits*)(& CGAL::Polygon_2<CGAL::Cartesian<double>,
> boost::container::static_vector<CGAL::Point_2<CGAL::Cartesian<double> >,
> 100u> >::Traits())))'
> note: candidate is:
> CGAL-4.2/include/CGAL/Polygon_2.h:68:7: note:
> CGAL::Polygon_2<CGAL::Cartesian<double>,
> boost::container::static_vector<CGAL::Point_2<CGAL::Cartesian<double> >,
> 100u> >& CGAL::Polygon_2<CGAL::Cartesian<double>,
> boost::container::static_vector<CGAL::Point_2<CGAL::Cartesian<double> >,
> 100u> >::operator=(CGAL::Polygon_2<CGAL::Cartesian<double>,
> boost::container::static_vector<CGAL::Point_2<CGAL::Cartesian<double> >,
> 100u> >&)
> CGAL-4.2/include/CGAL/Polygon_2.h:68:7: note: no known conversion for
> argument 1 from 'sensor::Polygon2d {aka
> CGAL::Polygon_2<CGAL::Cartesian<double>,
> boost::container::static_vector<CGAL::Point_2<CGAL::Cartesian<double> >,
> 100u> >}' to 'CGAL::Polygon_2<CGAL::Cartesian<double>,
> boost::container::static_vector<CGAL::Point_2<CGAL::Cartesian<double> >,
> 100u> >&'
> [/error]
>
> I apologize for this concrete example using CGAL, but maybe someone has
> advice for me?
>

Hello Jupp,

I don't know anything about CGAL, but I have a guess for you, where I
assume you're *not* in C++11 mode. I think I saw a similar error with my
structures and mingw-4.7. Please see this example (warning: it's out of my
head, not tested):

struct X
{
  static_vector<int,3> v;
};

int main()
{
  X x, y;
  x = y; // similar compile error
}

 If you get a similar error compiling the example above, I believe I can
explain it. I looks to me like the fault of move emulation in
static_vector. I'm not sure if it's a bug in static_vector, or if that's
the cost of using Boost.Move, but I remember writing my own operator= in
struct X helped:

struct X
{
  static_vector<int,3> v;
  X& operator=( X const& x ) { v = x.v; return *this; }
};

I think this is needed, because due to using Boost.Move in emulation mode
static_vector defines
static_vector& operator=(static_vector&); // note: non-const arg
so the auto-generated operaotr= in X also takes a non-const

HTH,
Kris