2. リファレンス
3. iterator
4. basic_const_iterator
5. common_type

最終更新日時: 2026年08月18日 11時14分29秒 (JST)
Akira Takahashi が更新

履歴 編集

std::common_type(C++23)

namespace std {
  // (1)
  template<class T, common_with<T> U>
    requires input_iterator<common_type_t<T, U>>
  struct common_type<basic_const_iterator<T>, U> {
    using type = basic_const_iterator<common_type_t<T, U>>;
  };

  // (2)
  template<class T, common_with<T> U>
    requires input_iterator<common_type_t<T, U>>
  struct common_type<U, basic_const_iterator<T>> {
    using type = basic_const_iterator<common_type_t<T, U>>;
  };

  // (3)
  template<class T, common_with<T> U>
    requires input_iterator<common_type_t<T, U>>
  struct common_type<basic_const_iterator<T>, basic_const_iterator<U>> {
    using type = basic_const_iterator<common_type_t<T, U>>;
  };
}

#include <iterator>

int main() {
  using ct1 = std::common_type_t<int*, std::const_iterator<int*>>;

  static_assert(std::same_as<ct1, std::basic_const_iterator<int*>>);

  using ct2 = std::common_type_t<std::const_iterator<int*>, int*>;

  static_assert(std::same_as<ct1, ct2>);

  using ct3 = std::common_type_t<const int*, std::const_iterator<int*>>;

  static_assert(std::same_as<ct3, std::basic_const_iterator<const int*>>);

  using ct4 = std::common_type_t<std::basic_const_iterator<int*>, std::basic_const_iterator<const int*>>;

  static_assert(std::same_as<ct4, std::basic_const_iterator<const int*>>);
}