Re: [Boost-users] Register variadic template as tags in a boost::mpl::map

7 Jan 2012


      Ahh.... found it.

Just a typo
...
template<int OFFSET>
struct B {
   typedef AA T;   // !   Must be BB...
   enum O { offset = OFFSET };
   enum S { size = 4 };
};
Sorry for wasting your time


On Sat, Jan 7, 2012 at 12:55 PM, Allan Nielsen  wrote:
...
In the following code, why can't I look up BB and CC in the mpl::map type_map?
I would expect the map to look like this:
map <
      pair >,
      pair >,
      pair > >
But it does not seem like this is the case...
#include <iostream>
#include 
#include 
#include 
#include 
struct AA {};
struct BB {};
struct CC {};
template<int OFFSET>
struct A {
   typedef AA T;
   enum O { offset = OFFSET };
   enum S { size = 2 };
};
template<int OFFSET>
struct B {
   typedef AA T;
   enum O { offset = OFFSET };
   enum S { size = 4 };
};
template<int OFFSET>
struct C {
   typedef AA T;
   enum O { offset = OFFSET };
   enum S { size = 4 };
};
template < template <int> class Head,
          template <int> class... Tail>
struct X : public Head< X::size * X::offset >,
          public X
{
   typedef Head< X::size * X::offset > _Head;
   enum O { offset = X::size * X::offset };
   enum S { size   = _Head::size * X::size };
   typedef typename boost::mpl::insert < typename X::type_map,
                                         boost::mpl::pair
...
::type type_map;
   template <typename T> int get_offset() {
       return boost::mpl::at::type:: offset;
   }
};
// base case
template < template <int> class Head>
struct X<Head> : public Head<1> {
   enum O { offset = Head<1>::offset };
   enum S { size   = Head<1>::size };
   typedef boost::mpl::map< boost::mpl::pair< typename Head<1>::T,
                                              Head<1> > > type_map;
};
int main()
{
   X< A, B, C > x1;
   std::cout << x1.get_offset<CC>() << std::endl;
   // generates compile errors
   //std::cout << x1.get_offset<BB>() << std::endl;
   //std::cout << x1.get_offset<CC>() << std::endl;
   return 0;
}