#include <iostream>
#include <vector>
#include <type_traits>
 
template<typename T>
struct Typer { typedef T type; };
 
template<typename T>
struct Typer<const T> { typedef T type; };
 
template<typename Iter>
void sumout(Iter first, Iter last) {
    typedef typename Typer<typename Iter::value_type>::type Value;
 
    Value v = 0;
    for (; first != last; (void) ++first) { v += *first; }
 
    bool cv = std::is_const<Value>::value;
    std::cout << (cv ? "const " : "") << typeid(v).name() << ": " << v;
}
 
int main() {
    std::vector<int> v = { 1, 2, 3 };
    sumout(v.cbegin(), v.cend());
}

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