[Boost-bugs] [Boost C++ Libraries] #1469: [mpl] nested typedef of set has two different meanings

Subject: [Boost-bugs] [Boost C++ Libraries] #1469: [mpl] nested typedef of set has two different meanings
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2007-11-22 13:25:20

#1469: [mpl] nested typedef of set has two different meanings
------------------------------------------+---------------------------------
 Reporter:  sven.vanechelpoel_at_[hidden]  |       Owner:  agurtovoy
     Type:  Bugs                          |      Status:  new      
Milestone:  To Be Determined              |   Component:  mpl      
  Version:  Boost 1.34.1                  |    Severity:  Problem  
 Keywords:                                |  
------------------------------------------+---------------------------------
 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

-- 
Ticket URL: <http://svn.boost.org/trac/boost/ticket/1469>
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