//Purpose:
//  Prototype the can_be_called method here:
/*
http://www.boost.org/doc/libs/1_41_0/doc/html/proto/appendices.html#boost_proto.appendices.implementation.function_arity
 */
#include <boost/mpl/bool.hpp>
#include <boost/mpl/package_range_c.hpp>
 
struct dont_care
{
    dont_care(...);
};

struct private_type
{
    private_type const &operator,(int) const;
};

typedef char yes_type;      // sizeof(yes_type) == 1
typedef char (&no_type)[2]; // sizeof(no_type)  == 2

template<typename T>
no_type is_private_type(T const &);

yes_type is_private_type(private_type const &);


template<typename Fun, unsigned N, typename... Args>
struct funwrap_dont_care
;
template<typename Fun, unsigned N, typename... Args>
struct funwrap_dont_care
: funwrap_dont_care<Fun, N-1, dont_care, Args...>
{
};
template<typename Fun, typename... Args>
struct funwrap_dont_care<Fun, 0, Args...>
: Fun
{
    funwrap_dont_care();
    typedef private_type const &(*pointer_to_function)(Args...);
    operator pointer_to_function() const;
};

template<unsigned Index, typename Sequence>
struct at_type_value
;
template<typename Head, typename... Tail>
struct at_type_value<0, boost::mpl::package<Head, Tail...> >
{
    typedef Head type;
    static type value(void);
};
template<unsigned Index, typename Head, typename... Tail>
struct at_type_value<Index, boost::mpl::package<Head, Tail...> >
: at_type_value<Index-1, boost::mpl::package<Tail...> >
{
};


template<typename Fun, typename Indices, typename Args>
struct can_be_called_impl
;
template<typename Fun, unsigned... Indices, typename Args>
struct can_be_called_impl<Fun, boost::mpl::package_c<unsigned, Indices...>, Args>
{
    static unsigned const arity=sizeof...(Indices);
    static funwrap_dont_care<Fun,arity> &fun;
    static bool const value = (
        sizeof(no_type) == sizeof(is_private_type( (fun(at_type_value<Indices,Args>::value()...), 0) ))
    );

    typedef boost::mpl::bool_<value> type;
};
template<typename Fun, typename... Args>
struct can_be_called
: can_be_called_impl
  < Fun
  , typename boost::mpl::package_range_c
    < unsigned
    , 0
    , sizeof...(Args)
    >::type
  , boost::mpl::package<Args...>
  >
{
};