Вывод типа элемента контейнера из итератора на контейнер

#include <vector>
#include <string>
 
using namespace std;
 
template <typename IteratorType>
void some_foo(IteratorType begin, IteratorType end)
{
    //value_type = string
    //key_type = char
    using value_type = typename iterator_traits<IteratorType>::value_type;
    pair<key_type, value_type> p;
}
 
int main()
{
    vector<string> vec = {"abc","cba"};
    some_foo(vec.begin(), vec.end());
 
    return 0;
}

template <typename IteratorType>
void some_foo(IteratorType begin, IteratorType end)
{
    using value_type = typename iterator_traits<IteratorType>::value_type;
 
    using key_type1 = typename iterator_traits<typename value_type::iterator>::value_type;
    using key_type2 = std::remove_reference_t<decltype(*std::declval<value_type>().begin())>;
 
    static_assert (is_same_v<key_type1, key_type2>);
    static_assert (is_same_v<unsigned long long, key_type1> || is_same_v<char, key_type1>);
}
 
int main()
{
    vector<string> vec = {"abc","cba"};
    vector<list<unsigned long long>> vl;
    some_foo(vec.begin(), vec.end());
    some_foo(vl.begin(), vl.end());
    return 0;
}