#include <algorithm>
#include <iostream>
#include <functional>
#include <vector>
 
template <class T>
struct twicer : std::unary_function<T,T>
{
	T operator()( const T& t ) const { return t * 2; }
};
 
template <class _Tp, class FT>
struct myplus : public std::binary_function<_Tp, _Tp, _Tp>
{
  _Tp operator()(const _Tp& __x, const _Tp& __y) const
  { return __x + funktor(__y); }
 
  FT funktor;
};
 
int main() {
 
	std::vector<int> v = {1,2};
 
	std::cout << std::accumulate( v.begin(), v.end(), 0, myplus<int,twicer<int> >() ) << std::endl;
	//std::cout << std::accumulate( v.begin(), v.end(), 0, std::plus<int>() ) << std::endl;
 
	return 0;
}

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