std::unordered_map::推論補助(C++17)

namespace std {
  // 説明用の型
  template <class InputIterator>
  using iter_key_t = remove_const_t<typename iterator_traits<InputIterator>::value_type::first_type>;
  template <class InputIterator>
  using iter_val_t = typename iterator_traits<InputIterator>::value_type::second_type;
  template <class InputIterator>
  using iter_to_alloc_t = pair<add_const_t<typename iterator_traits<InputIterator>::value_type::first_type>,
                               typename iterator_traits<InputIterator>::value_type::second_type>;

  template <class InputIterator,
            class Hash = hash<iter_key_t<InputIterator>>,
            class Pred = equal_to<iter_key_t<InputIterator>>,
            class Allocator = allocator<iter_to_alloc_t<InputIterator>>>
  unordered_map(InputIterator, InputIterator, typename see below::size_type = see below,
                Hash = Hash(), Pred = Pred(), Allocator = Allocator())
    -> unordered_map<iter_key_t<InputIterator>,
                     iter_value_t<InputIterator>,
                     Hash, Pred, Allocator>;         // (1)

  template <class Key, class T,
            class Hash = hash<Key>,
            class Pred = equal_to<Key>,
            class Allocator = allocator<pair<const Key, T>>>
  unordered_map(initializer_list<pair<Key, T>>,
                typename see below::size_type = see below,
                Hash = Hash(), Pred = Pred(), Allocator = Allocator())
    -> unordered_map<Key, T, Hash, Pred, Allocator>; // (2)

  template <class InputIterator, class Allocator>
  unordered_map(InputIterator, InputIterator, typename see below::size_type, Allocator)
    -> unordered_map<
           iter_key_t<InputIterator>,
           iter_val_t<InputIterator>,
           hash<iter_key_t<InputIterator>>,
           equal_to<iter_key_t<InputIterator>>,
           Allocator>;                               // (3)

  template <class InputIterator, class Allocator>
  unordered_map(InputIterator, InputIterator, Allocator)
    -> unordered_map<
           iter_key_t<InputIterator>,
           iter_val_t<InputIterator>,
           hash<iter_key_t<InputIterator>>,
           equal_to<iter_key_t<InputIterator>>,
           Allocator>;                               // (4)

  template <class InputIterator, class Hash, class Allocator>
  unordered_map(InputIterator, InputIterator, typename see below::size_type, Hash, Allocator)
    -> unordered_map<
           iter_key_t<InputIterator>,
           iter_val_t<InputIterator>,
           Hash,
           equal_to<iter_key_t<InputIterator>>,
           Allocator>;                               // (5)

  template <class Key, class T, typename Allocator>
  unordered_map(initializer_list<pair<Key, T>>, typename see below::size_type, Allocator)
    -> unordered_map<Key, T, hash<Key>,
                     equal_to<Key>, Allocator>;      // (6)

  template <class Key, class T, typename Allocator>
  unordered_map(initializer_list<pair<Key, T>>, Allocator)
    -> unordered_map<Key, T, hash<Key>,
                     equal_to<Key>, Allocator>;      // (7)

  template <class Key, class T, class Hash, class Allocator>
  unordered_map(initializer_list<pair<Key, T>>, typename see below::size_type, Hash, Allocator)
    -> unordered_map<Key, T, Hash,
                     equal_to<Key>, Allocator>;      // (8)
}