#include <boost/bind.hpp>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/hashed_index.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/type_traits/remove_cv.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <iostream>
#include <string>

struct foo
{
  std::string s;
  foo(std::string s):s(s){}
};

#define DEFINE_BIND_TYPE(name,expr)                             \
typedef boost::remove_reference<                                \
  boost::remove_cv<typeof(expr)>::type>::type name##_expr_type; \
                                                                \
struct name:name##_expr_type                                    \
{                                                               \
  name():name##_expr_type(expr){}                               \
};

using namespace boost::multi_index;

DEFINE_BIND_TYPE(
  extractor,
  boost::bind(&std::string::size,boost::bind(&foo::s,_1)))

typedef multi_index_container<
  foo,
  indexed_by<
    hashed_unique<extractor>
  >
> mi_t;

int main()
{
  mi_t m;
  m.insert(foo("hello"));
  m.insert(foo("goodbye"));
  m.insert(foo("C++"));

  std::cout<<m.find(3)->s<<std::endl;
}