[Boost-users] [mpl] find_all type vectors in a type matrix that match a predicate.

From: Christian Henning (chhenning_at_[hidden])
Date: 2007-04-01 13:48:19

Hi there,

is it possible to find all type vectors in a type matrix ( 2D type
vector ) that match a predicate? In the end I would like to have them
in another type matrix.

Can somebody point out how I would put together such a metafunction?
I'm not sure if the mpl lib supports my feature request.

Consider the following code:

#include "boost/mpl/vector.hpp"
#include <boost/mpl/find_if.hpp>
#include <boost/mpl/at.hpp>

using namespace std;
using namespace boost;

namespace fields
{
  struct id {};
  struct name {};
  struct address {};
  struct birthday {};
}

namespace tags
{
  struct primary {};
  struct foreign {};
  struct no_key {};
}

typedef mpl::vector<fields::id      , tags::primary> id_field_t;
typedef mpl::vector<fields::name    , tags::foreign> name_field_t;
typedef mpl::vector<fields::address , tags::foreign> address_field_t;
typedef mpl::vector<fields::birthday, tags::no_key> birthday_field_t;

typedef mpl::vector< id_field_t
                   , name_field_t
                   , address_field_t
                   , birthday_field_t
                   > table;

// aggregate all foreign keys in the following vector
typedef mpl::vector0<> foreign_keys;

/// ??? metafunction for aggregating all foreign keys ???

int main()
{
   return 0;
}

BTW, I'm not particular interested in a certain order of the
aggregated type vectors.

Reagrds,
Christian