#include <boost/function_arity.hpp>
#include <boost/bind.hpp>
#include <boost/function.hpp>
#include <iostream>

void fn_1(int){}
void fn_2(int,int){}
void fn_0(){}

namespace _bi=boost::_bi;

template<class ListType>
struct list_size;

template<>struct list_size<_bi::list0>{enum {value=0};};
template<typename A1>struct list_size<_bi::list1<A1> >{enum {value=1};};
template<typename A1,typename A2>struct list_size<_bi::list2<A1,A2> >{enum {value=2};};

template<class R, class F, class L>
size_t get_bind_nargs(_bi::bind_t<R,F,L> const &)
{
    return list_size<L>::value;
}

int main()
{
    std::cout << get_bind_nargs(boost::bind(&fn_0)) << std::endl;
    std::cout << get_bind_nargs(boost::bind(&fn_1,_1)) << std::endl;
    std::cout << get_bind_nargs(boost::bind(&fn_2,_1,_2)) << std::endl;
}