Playing with C++11 type traits and templates

cpp11-type-traits.cpp

#include <iostream>
#include <iterator>
#include <vector>
#include <set>

// overload for all STL containers
template <
  typename T,
  typename = typename std::enable_if <
    std::is_convertible<
      typename std::iterator_traits<
        typename T::iterator
      >::iterator_category,
      std::input_iterator_tag
    >::value, bool
  >::type
>
std::ostream& operator<< (std::ostream &s, const T& ref) {
  s << "(generic) [";
  for (auto it = ref.begin(); it != ref.end(); it++) {
    s << (it != ref.begin() ? ", " : "") << *it;
  }
  return s << "]";
}

// vector-only, with type traits
// template <
//   typename Y,
//   typename std::enable_if<
//     std::is_convertible<
//       Y,
//       std::vector<
//         typename std::iterator_traits<
//           typename Y::iterator
//         >::value_type
//       >
//     >::value, bool
//   >::type
// >
// std::ostream& operator<< (std::ostream &s, const Y& ref) {
//   s << "(vector) [";
//   for (auto it = ref.begin(); it != ref.end(); it++) {
//     s << (it != ref.begin() ? ", " : "") << *it;
//   }
//   return s << "]";
// }

// vector-only
template <typename T>
std::ostream& operator<< (std::ostream &s, const std::vector<T>& v) {
  s << "(vector) [";
  for (auto it = v.begin(); it != v.end(); it++) {
    s << (it != v.begin() ? ", " : "") << *it;
  }
  return s << "]";
}

int main (void) {
  std::vector<double> v{1.1, 2.2, 3.3};
  std::set<int> s{1, 2, 3};
  std::vector<std::set<int>> vs{s, {5, 6, 7}, s};

  std::cout <<  v << std::endl;
  std::cout <<  s << std::endl;
  std::cout << vs << std::endl;

  // (vector) [1.1, 2.2, 3.3]
  // (generic) [1, 2, 3]
  // (vector) [(generic) [1, 2, 3], (generic) [5, 6, 7], (generic) [1, 2, 3]]
  return 0;
}