Restrict Template Function

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This is possible by using SFINAE, and made easier by using helpers from either Boost or C++11

Boost:

#include <vector>
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_arithmetic.hpp>

template<typename T> 
    typename boost::enable_if<typename boost::is_arithmetic<T>::type, T>::type 
        sum(const std::vector<T>& vec)
{
  typedef typename std::vector<T>::size_type size_type;
  T result;
  size_type size = vec.size();
  for(size_type i = 0; i < size; i++)
  {
    result += vec[i];
  }

  return result;
}

C++11:

#include <vector>
#include <type_traits>

template<typename T> 
    typename std::enable_if<std::is_arithmetic<T>::value, T>::type 
        sum(const std::vector<T>& vec)
{
  T result;
  for (auto item : vec)
    result += item;
  return result;
}

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