[Boost-users] mpl::switch question

From: Istvan Buki (istvan.buki_at_[hidden])
Date: 2004-08-18 09:53:49

Hello,

I've just tried to compile a small piece of code using mpl::switch_ 
starting from an example Aleksey Gurtovoy sent to this list a while ago.

I slightly modified the code to use the boost::is_same<T,U> template but 
I can't make it compile. On the other hand, if I comment out the line in 
the switch_body containing the is_same template, it compile without any 
problem.

I spent the whole day on this and I'm lost. Any help would be welcome.

Thanks,
Istvan

PS: I'm using boost 1.30.2 and g++ 3.3.3.

#include "boost/mpl/vector.hpp"
#include "boost/mpl/switch.hpp"
#include "boost/mpl/project1st.hpp"
#include "boost/mpl/pair.hpp"
#include "boost/mpl/always.hpp"
#include "boost/mpl/bool.hpp"
#include "boost/mpl/assert_is_same.hpp"

#include "boost/type_traits/remove_reference.hpp"
#include "boost/type_traits/add_const.hpp"
#include "boost/type_traits/is_pointer.hpp"
#include "boost/type_traits/is_reference.hpp"
#include "boost/type_traits/is_same.hpp"

using namespace boost::mpl ;
using boost::mpl::_ ;

struct MyType
{
   typedef int type ;
} ;

int main()
{
   typedef vector<
   pair< boost::is_pointer<_1>, _1 >
     // If the following line is commented out it compile.
     , pair< boost::is_same<_1, _1 >, boost::add_const<_1> >
     , pair< boost::is_reference<_1>, boost::remove_reference<_1> >
     , pair< always<bool_<true > >, boost::add_const<_1> >
     > switch_body;

   typedef switch_< switch_body, char& >::type t1;
   typedef switch_< switch_body, int* >::type t2;
   typedef switch_< switch_body, int >::type t3;

   BOOST_MPL_ASSERT_IS_SAME(t1, char);
   BOOST_MPL_ASSERT_IS_SAME(t2, int*);
   BOOST_MPL_ASSERT_IS_SAME(t3, int const);
}