#include <iostream>
#include <unordered_set>
#include <boost/static_assert.hpp>
#include <boost/type_traits.hpp>
#include <cstddef>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/type_erasure/is_placeholder.hpp>
#include <boost/type_erasure/any.hpp>
#include <boost/type_erasure/member.hpp>
#include <boost/type_erasure/free.hpp>
#include <boost/type_erasure/operators.hpp>
#include <boost/type_erasure/any_cast.hpp>
#include <boost/type_erasure/iterator.hpp>
#include <boost/functional/hash.hpp>

namespace te = boost::type_erasure;
namespace mpl = boost::mpl;

BOOST_TYPE_ERASURE_MEMBER((has_insert), insert, 1)
BOOST_TYPE_ERASURE_MEMBER((has_count), count, 1)
BOOST_TYPE_ERASURE_MEMBER((has_find), find, 1)

template<class T>
struct get_value_type_impl {
  typedef typename T::value_type type;
};

template<class T>
struct get_value_type {
  typedef typename mpl::eval_if<te::is_placeholder<T>,
    mpl::identity<void>,
    get_value_type_impl<T>
  >::type type;
};

typedef te::deduced<get_value_type<te::_self> > _value;

struct requirements :
  boost::mpl::vector<
    te::copy_constructible<>, //we can copy sets
    te::relaxed, //various other common features
    te::typeid_<>, //they can be dynamic cast
    has_count<std::size_t(const _value&)> //count copies of key in the set
    // has_insert<std::pair<te::iterator<boost::forward_traversal_tag>,bool>(const _value&)>, //insert a key
    >
{};

typedef te::any<requirements> any_set;
typedef te::any<requirements, _value> erased_value;


int main(int argc, const char *argv[]) {
  
  std::unordered_set<int> h;
  any_set history(h);

  BOOST_STATIC_ASSERT((boost::is_same<get_value_type<std::unordered_set<int> >::type, int>::value));

  history.count(1);
}