hash_multimap and concept checking

I've come across a problem with gcc 4.1.1, hash_multimap and concept
checking. The following code fails to compile when g++ is invoked as

g++ -D_GLIBCXX_CONCEPT_CHECKS concepts.cpp

and concepts.cpp is

#include <ext/hash_map>
namespace Sgi=::__gnu_cxx;

struct foo
{
    const int i;
};

typedef Sgi::hash_multimap<int, foo> map_t;

int main()
{
    map_t my_map;
}

The immediate reason is that <ext/hash_map> contains the lines:

template <class _Key, class _Tp, class _HashFcn, class _EqualKey,
          class _Alloc>
class hash_multimap
    {
      // concept requirements
      __glibcxx_class_requires(_Key, _SGIAssignableConcept)
      __glibcxx_class_requires(_Tp, _SGIAssignableConcept)
      __glibcxx_class_requires3(_HashFcn, size_t, _Key,
_UnaryFunctionConcept)
      __glibcxx_class_requires3(_EqualKey, _Key, _Key,
_BinaryPredicateConcept)

But I can see nothing in the SGI documentation, or in Matthew
Austern's 2001 WG21 hashtable proposal, implying that the data element
in a hash_multimap should be assignable. Using hash_map in lieu of
hash_multimap compiles fine: there are no equivalent concept checking
statements.

Is this Assignable requirement on Data, imposed by g++ 4.1.1, a
feature of the proposed standard hash_multimap?

--
Giles Chamberlin

      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated. First time posters: Do this! ]