std::vector<decltype(iter)> - valid usage of decltype?

Question

This is the first time I am using decltype, and I am not quite sure whether I am using it right. The code does compile and seems to work for POD like char and int.

I am, however, wondering whether I might run into any problems with more complex data types - I have been warned by others that things like auto and decltype can quickly get unintended results.

My assumption is that this template would work for any type T that has the operator!= defined. Are there any fringe cases I should be concerned about?

#include <forward_list>
#include <iostream>
#include <cstdlib>
#include <vector>

template<typename T>
bool isPalindrome(const std::forward_list<T>& lf)
{
  auto iter = lf.begin();
  std::vector<decltype(iter)> bv; // <-- Correct usage?

  while(iter!= lf.end())
    { bv.push_back(iter++); }

  int istop = bv.size()/2 + bv.size()%2;
  iter = lf.begin();

  for(int i = bv.size()-1; i>=istop; i--, iter++)
  { if( *iter != *(bv[i])) return false; }
  return true;
}

int main(int argc, char* argv[])
{
  std::forward_list<int> list = {0,1,2,1,0};
  std::cout << "Is palindrome: " << isPalindrome(list) << std::endl;
  return 1;
}

Answer 1

Yes, there is no problem with that usage. You will be using a std::vector of std::forward_list::iterator, and since those iterators meet container requirements, you are good to go.