[mpl] nested typedef of set has two different meanings

[sven.vanechelpoel@…]

This problem was diagnosed by Steve Watanabe after my posting on the developer list (see ​http://thread.gmane.org/gmane.comp.lib.boost.devel/168339/focus=168366)

Basically the following doesn't compile:

#include <boost/mpl/set.hpp>
#include <boost/mpl/vector.hpp>
#include <boost/mpl/copy.hpp>
#include <boost/mpl/insert.hpp>
#include <boost/mpl/inserter.hpp>

using namespace boost::mpl;

template<
  typename T
> >
struct as_set :
  copy<
    T
  , inserter<
      set<>
    , insert< _1, _2 >
    >
  >
{};

typedef set<int,char>             a_set;
typedef vector<int,int,char>      a_vector;
typedef as_set< a_set >::type     set_as_set;
typedef as_set< a_vector >::type  vector_as_set;

typedef next< begin< a_set >::type >::type
THIS_IS_OK;
typedef next< next< begin< a_set >::type >::type >::type
THIS_IS_OK_AS_WELL;
typedef next< begin< a_vector >::type >::type
THIS_IS_OK_TOO;
typedef next< begin< set_as_set >::type >::type
THIS_WORKS_TOO;
typedef next< next< begin< set_as_set >::type >::type >::type
THIS_FAILS;
typedef next< next< begin< vector_as_set >::type >::type >::type
THIS_FAILS_TOO;

Steve Watanabe diagnosed this to be a problem of mpl::set using the nested typedef 'type' for two different purposes: one as an alias of the set<>, the other refering to the item type. The result is that upon iteration the termination condition isn't recognized and the iterator blows up