#include<iostream>
#include<vector>



template<bool flag,typename T1,typename T2> struct If_then_else {
typedef T1 Result; 
};

template<typename T1,typename T2> 
struct If_then_else<false,T1,T2> {
typedef T2 Result; 
};


template<typename T1,typename T2> struct Promote {
typedef typename 
        If_then_else<(sizeof(T1) > sizeof(T2)),
                     T1,
                     typename If_then_else< (sizeof(T1)< sizeof(T2)),
                                           T2,
                                           void>::Result >::Result Result;
};

template<typename T> struct Promote<T,T> {
  typedef T Result;
};




#define MK_PROMOTION(T1,T2,Tr)             \
    template<> class Promote<T1, T2> {   \
      public:                              \
        typedef Tr ResultT;                \
    };                                     \
                                           \
    template<> class Promote<T2, T1> {   \
      public:                              \
        typedef Tr ResultT;                \
    };

MK_PROMOTION(bool, char, int)
MK_PROMOTION(bool, unsigned char, int)
MK_PROMOTION(bool, signed char, int)



template<typename T> std::vector<T> 
operator+(const std::vector<T>  &a,
	   const std::vector<T>  &b) {


  assert(a.size()==b.size());

  std::vector<T> res(a);
  for(size_t i=0;i<a.size();++i)
    res[i]+=b[i];

  return res;
}



template<typename T,typename U> 
std::vector<typename Promote<T,U>::Result>
operator+(const std::vector<T>  &a,
	  const std::vector<U>  &b) {

  assert(a.size()==b.size());

  std::vector<typename Promote<T,U>::Result> res(a.size());
  for(size_t i=0;i<a.size();++i)
    res[i]=a[i]+b[i];

  return res;
}


main() {
  std::vector<double> x(10);
  std::vector<double> y(10);
  std::vector<int>    l(10);

  x+y;
  l+x;


}