// is_container
// ============
template <typename T>
struct is_container {
  static constexpr TYPE value = is_type<T>::value;
};

// check_type
// ============
template<class C1, class C2>
typename std::enable_if
  <is_container<C1>::value == SET
  && is_container<C2>::value == SET, bool>::type
check_type() {
  return true;
}

template<class C1, class C2>
typename std::enable_if
  <is_container<C1>::value == MAP
  && is_container<C2>::value == MAP, bool>::type
check_type() {
  return true;
}

template<class C1, class C2>
typename std::enable_if
  <is_container<C1>::value == MMAP
  && is_container<C2>::value == MMAP, bool>::type
check_type() {
  return true;
}

template<class C1, class C2>
typename std::enable_if
  <is_container<C1>::value == MMAP
  && is_container<C2>::value == MAP, bool>::type
check_type() {
  return true;
}

template<class C1, class C2>
typename std::enable_if
  <is_container<C1>::value == MSET
  && is_container<C2>::value == MSET, bool>::type
check_type() {
  return true;
}

template<class C1, class C2>
typename std::enable_if
  <is_container<C1>::value == MSET
  && is_container<C2>::value == SET, bool>::type
check_type() {
  return true;
}

template<class C1, class C2>
bool check_type() {
  return false;
}