Bespreek dit programma. Wat is de functie van base_type? 

#include <string>
#include <sstream>
#include <iostream>

template <typename T>
struct base_type {
  typedef T mutable_type;
};

template <typename T>
struct base_type<const T> {
  typedef T mutable_type;
};

template<class T> 
T
parse(const std::string& s) {
typename base_type<T>::mutable_type t;
std::istringstream iss(s);
iss >> t;
return t;
}

int
main(int,char**) {
const int x(parse<const int>("3"));
std::cout << x << std::endl;
}