标准库标头 <ranges> (C++20)

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标准库头
通用工具
<any> (C++17)
<bitset>
<bit> (C++20)
<charconv> (C++17)
<expected> (C++23)
<format> (C++20)
<functional>
<optional> (C++17)
<stdbit.h> (C++26)
<tuple> (C++11)
<typeindex> (C++11)
<utility>
<variant> (C++17)
容器
<array> (C++11)
<deque>
<flat_map> (C++23)
<flat_set> (C++23)
<forward_list> (C++11)
<hive> (C++26)
<inplace_vector> (C++26)   
<list>
<map>
<mdspan> (C++23)
<queue>
<set>
<span> (C++20)
<stack>
<unordered_map> (C++11)
<unordered_set> (C++11)
<vector>
迭代器
<iterator>
范围
<generator> (C++23)
<ranges> (C++20)
 

此头文件是范围库的一部分。

命名空间别名

<tbody> </tbody>
namespace std { namespace views = ranges::views; }

提供命名空间别名 std::views，作为 std::ranges::views 的简称。

包含

(C++20)
 三路比较运算符支持[编辑]
(C++11)
 std::initializer_list 类模板[编辑]
范围迭代器[编辑]

概念

范围概念
在命名空间 std::ranges 定义
(C++20)
 指定类型为范围，即它同时提供 begin 迭代器和 end 哨位
(概念) [编辑]
(C++20)
 指定类型为 range 而且能安全返回从该类型表达式获得的迭代器而无需担心悬垂
(概念) [编辑]
(C++26)
 指定范围可以常数时间估算大小
(概念) [编辑]
(C++20)
 指定范围可以常数时间计算大小
(概念) [编辑]
(C++20)
 指定范围为视图，即它拥有常数时间的复制/移动/赋值
(概念) [编辑]
(C++20)
 指定范围的迭代器类型满足 input_iterator
(概念) [编辑]
(C++20)
 指定范围的迭代器类型满足 output_iterator
(概念) [编辑]
(C++20)
 指定范围的迭代器类型满足 forward_iterator
(概念) [编辑]
(C++20)
 指定范围的迭代器类型满足 bidirectional_iterator
(概念) [编辑]
(C++20)
 指定范围的迭代器类型满足 random_access_iterator
(概念) [编辑]
(C++20)
 指定范围的迭代器类型满足 contiguous_iterator
(概念) [编辑]
(C++20)
 指定范围拥有相同的迭代器和哨位类型
(概念) [编辑]
(C++20)
 指定针对 range 的要求，令其可安全转换为 view
(概念) [编辑]
(C++23)
 指定范围的所有元素只读
(概念) [编辑]

函数

范围转换器
在命名空间 std::ranges 定义
(C++23)
 从输入范围构造一个新的非视图对象
(函数模板) [编辑]

类

范围原语
在命名空间 std::ranges 定义
(C++20)(C++23)(C++20)(C++23)
 获取范围的迭代器和哨位类型
(别名模板) [编辑]
(C++20)(C++20)(C++20)
 取得范围的大小类型、差类型和值类型
(别名模板) [编辑]
(C++20)(C++23)(C++20)(C++20)
 取得范围的引用类型
(别名模板) [编辑]
视图
在命名空间 std::ranges 定义
(C++20)
 用于定义 view 的辅助类模板，使用奇特重现模板模式
(类模板) [编辑]
(C++20)
 将迭代器/哨位对结合为一个 view
(类模板) [编辑]
悬垂迭代器处理
在命名空间 std::ranges 定义
(C++20)
 占位类型，指示不应返回迭代器或子范围，因为它可能悬垂
(类) [编辑]
(C++20)
 获得塑造 borrowed_range 的迭代器类型或子范围类型
(别名模板) [编辑]
其他工具
在命名空间 std::ranges 定义
(C++23)
 标记范围为当作序列而非单个值对待
(类模板) [编辑]
工厂
在命名空间 std::ranges 定义
(C++20)
 无元素的空 view
(类模板) (变量模板) [编辑]
(C++20)
 含有具有指定值的单个元素的 view
(类模板) (定制点对象) [编辑]
(C++20)
 由通过重复对某个初值自增所生成的序列组成的 view
(类模板) (定制点对象) [编辑]
(C++23)
 由重复产出同一值生成的序列组成的 view
(类模板) (定制点对象) [编辑]
(C++20)
 由在关联的输入流上相继应用 operator>> 获得的元素组成的 view
(类模板) (定制点对象) [编辑]
适配器
在命名空间 std::ranges 定义
(C++23)
 用于定义范围适配器闭包对象的辅助基类模板
(类模板) [编辑]
(C++20)
 包含 range 的所有元素的 view
(别名模板) (范围适配器对象) [编辑]
(C++20)
 某个其他 range 的元素的 view
(类模板) [编辑]
(C++20)
 拥有某 range 的独占所有权的 view
(类模板) [编辑]
(C++23)
 由将序列所有元素转换为右值组成的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 由 range 中满足某个谓词的元素构成的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 对序列的每个元素应用某个变换函数的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 由另一 view 的前 N 个元素组成的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 由另一 view 的到首个谓词返回 false 为止的起始元素组成的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 由另一 view 跳过前 N 个元素组成的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 由另一 view 跳过元素的起始序列，直至首个使谓词返回 false 的元素组成的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 由拉平 range 组成的 view 所获得的序列构成的 view
(类模板) (范围适配器对象) [编辑]
(C++23)
 由拉平范围组成的视图并以分隔符间隔所获得的序列构成的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 用某个分隔符切割另一 view 所获得的子范围的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 用某个分隔符切割另一 view 所获得的子范围的 view
(类模板) (范围适配器对象) [编辑]
(C++26)
 连接所适配各视图而组成的 view
(类模板) (定制点对象) [编辑]
(C++20)
 从迭代器和计数创建子范围
(定制点对象) [编辑]
(C++20)
 转换 view 为 common_range
(类模板) (范围适配器对象) [编辑]
(C++20)
 以逆序迭代另一双向视图上的元素的 view
(类模板) (范围适配器对象) [编辑]
(C++23)
 转换 view 为 constant_range
(类模板) (范围适配器对象) [编辑]
(C++20)
 选取 tuple-like 值组成的 view 和数值 N，产生每个元组的第 N 个元素组成的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 选取对偶式值组成的 view 并产生每个对偶的第一元素的 view
(类模板) (范围适配器对象) [编辑]
(C++20)
 接受一个由对偶式值组成的 view 并产生每个对偶的第二元素组成的 view
(类模板) (范围适配器对象) [编辑]
(C++23)
 将被适配视图的各元素映射为元素位置和其值组成的元组的 view
(类模板) (范围适配器对象) [编辑]
(C++23)
 到被适配视图的对应元素的引用元组组成的 view
(类模板) (定制点对象) [编辑]
(C++23)
 由应用变换函数到被适配视图的对应元素的结果组成的 view
(类模板) (定制点对象) [编辑]
(C++23)
 由到被适配视图的相邻元素的引用的元组组成的 view
(类模板) (范围适配器对象) [编辑]
(C++23)
 由应用变换函数到被适配视图的相邻元素的结果组成的 view
(类模板) (范围适配器对象) [编辑]
(C++23)
 另一个视图元素的 N 大小不重叠的连续块组成的 view 的范围
(类模板) (范围适配器对象) [编辑]
(C++23)
 第 M 个元素是另一 view 从第 M 到第 (M + N - 1) 个元素的 view 构成的 view
(类模板) (范围适配器对象) [编辑]
(C++23)
 在给定谓词返回 false 的每一对相邻元素处，将 view 切分为子范围
(类模板) (范围适配器对象) [编辑]
(C++23)
 由另一 view 的元素每次前进 N 步所获得的 view
(类模板) (范围适配器对象) [编辑]
(C++23)
 计算各适配视图的 n 元笛卡尔积所得的元组组成的 view
(类模板) (定制点对象) [编辑]
(C++26)
 缓存其底层序列最后一次访问的元素的 view
(类模板) (范围适配器对象) [编辑]
(C++26)
 转换 view 到仅实现 input_range 和不是 common_range 的范围
(类模板) (范围适配器对象) [编辑]

定制点对象

范围访问
在命名空间 std::ranges 定义
(C++20)
 返回指向范围起始的迭代器
(定制点对象) [编辑]
(C++20)
 返回指示范围结尾的哨位
(定制点对象) [编辑]
(C++20)
 返回指向只读范围起始的迭代器
(定制点对象) [编辑]
(C++20)
 返回指示只读范围结尾的哨位
(定制点对象) [编辑]
(C++20)
 返回指向范围的逆向迭代器
(定制点对象) [编辑]
(C++20)
 返回指向范围的逆向尾迭代器
(定制点对象) [编辑]
(C++20)
 返回指向只读范围的逆向迭代器
(定制点对象) [编辑]
(C++20)
 返回指向只读范围的逆向尾迭代器
(定制点对象) [编辑]
(C++26)
 返回等于给定范围的预备储存提示的整数
(定制点对象) [编辑]
(C++20)
 返回等于范围大小的整数
(定制点对象) [编辑]
(C++20)
 返回等于范围大小的有符号整数
(定制点对象) [编辑]
(C++20)
 检查范围是否为空
(定制点对象) [编辑]
(C++20)
 获得指向连续范围的起始的指针
(定制点对象) [编辑]
(C++20)
 获得指向只读连续范围的起始的指针
(定制点对象) [编辑]

枚举

在命名空间 std::ranges 定义
(C++20)
 指定 std::ranges::subrange 是否实现 std::ranges::sized_range
(枚举) [编辑]

辅助工具

(C++20)
 获得 std::ranges::subrange 的大小
(类模板特化) [编辑]
(C++20)
 获得 std::ranges::subrange 的迭代器或哨位的类型
(类模板特化) [编辑]
(C++20)
 从 std::ranges::subrange 获得迭代器或哨位
(函数模板) [编辑]
(C++23)
 指定来自范围的消歧义标签
(类) (常量) [编辑]

概要

// 几乎全为独立实现
#include <compare>
#include <initializer_list>
#include <iterator>

namespace std::ranges {
  inline namespace /* 未指定 */ {
    // 范围访问
    inline constexpr /* 未指定 */ begin        = /* 未指定 */;
    inline constexpr /* 未指定 */ end          = /* 未指定 */;
    inline constexpr /* 未指定 */ cbegin       = /* 未指定 */;
    inline constexpr /* 未指定 */ cend         = /* 未指定 */;
    inline constexpr /* 未指定 */ rbegin       = /* 未指定 */;
    inline constexpr /* 未指定 */ rend         = /* 未指定 */;
    inline constexpr /* 未指定 */ crbegin      = /* 未指定 */;
    inline constexpr /* 未指定 */ crend        = /* 未指定 */;

    inline constexpr /* 未指定 */ size         = /* 未指定 */;
    inline constexpr /* 未指定 */ reserve_hint = /* 未指定 */;
    inline constexpr /* 未指定 */ ssize        = /* 未指定 */;
    inline constexpr /* 未指定 */ empty        = /* 未指定 */;
    inline constexpr /* 未指定 */ data         = /* 未指定 */;
    inline constexpr /* 未指定 */ cdata        = /* 未指定 */;
  }

  // 范围
  template<class T>
  concept range = /* 见描述 */;

  template<class T>
  constexpr bool enable_borrowed_range = false;

  template<class T>
  concept borrowed_range = /* 见描述 */;

  template<class T>
  using iterator_t = decltype(ranges::begin(declval<T&>()));
  template<range R>
  using sentinel_t = decltype(ranges::end(declval<R&>()));
  template<range R>
  using const_iterator_t = decltype(ranges::cbegin(declval<R&>()));
  template<range R>
  using const_sentinel_t = decltype(ranges::cend(declval<R&>()));
  template<range R>
  using range_difference_t = iter_difference_t<iterator_t<R>>;
  template<sized_range R>
  using range_size_t = decltype(ranges::size(declval<R&>()));
  template<range R>
  using range_value_t = iter_value_t<iterator_t<R>>;
  template<range R>
  using range_reference_t = iter_reference_t<iterator_t<R>>;
  template<range R>
  using range_const_reference_t = iter_const_reference_t<iterator_t<R>>;
  template<range R>
  using range_rvalue_reference_t = iter_rvalue_reference_t<iterator_t<R>>;
  template<range R>
  using range_common_reference_t = iter_common_reference_t<iterator_t<R>>;

  // 有大小范围
  template<class>
  constexpr bool disable_sized_range = false;

  template<class T>
  concept approximately_sized_range = /* 见描述 */;

  template<class T>
  concept sized_range = /* 见描述 */;

  // 视图
  template<class T>
  constexpr bool enable_view = /* 见描述 */;

  struct view_base
  {};

  template<class T>
  concept view = /* 见描述 */;

  // 其他的范围提炼
  template<class R, class T>
  concept output_range = /* 见描述 */;

  template<class T>
  concept input_range = /* 见描述 */;

  template<class T>
  concept forward_range = /* 见描述 */;

  template<class T>
  concept bidirectional_range = /* 见描述 */;

  template<class T>
  concept random_access_range = /* 见描述 */;

  template<class T>
  concept contiguous_range = /* 见描述 */;

  template<class T>
  concept common_range = /* 见描述 */;

  template<class T>
  concept viewable_range = /* 见描述 */;

  template<class T>
  concept constant_range = /* 见描述 */;

  // 类模板 view_interface
  template<class D>
    requires is_class_v<D> && same_as<D, remove_cv_t<D>>
  class view_interface;

  // 子范围
  enum class subrange_kind : bool
  {
    unsized,
    sized
  };

  template<input_or_output_iterator I, sentinel_for<I> S = I, subrange_kind K =
             /* 见描述 */>
    requires(K == subrange_kind::sized || !sized_sentinel_for<S, I>)
  class subrange;

  template<class I, class S, subrange_kind K>
  constexpr bool enable_borrowed_range<subrange<I, S, K>> = true;

  template<size_t N, class I, class S, subrange_kind K>
    requires((N == 0 && copyable<I>) || N == 1)
  constexpr auto get(const subrange<I, S, K>& r);

  template<size_t N, class I, class S, subrange_kind K>
    requires(N < 2)
  constexpr auto get(subrange<I, S, K>&& r);
}

namespace std {
  using ranges::get;
}

namespace std::ranges {
  // 悬垂迭代器处理
  struct dangling;

  // 类模板 elements_of
  template<range R, class Allocator = allocator<byte>>
  struct elements_of; // 宿主实现

  template<range R>
  using borrowed_iterator_t = /* 见描述 */;

  template<range R>
  using borrowed_subrange_t = /* 见描述 */;

  // 范围转换
  template<class C, input_range R, class... Args>
    requires(!view<C>)
  constexpr C to(R&& r, Args&&... args);
  template<template<class...> class C, input_range R, class... Args>
  constexpr auto to(R&& r, Args&&... args);
  template<class C, class... Args>
    requires(!view<C>)
  constexpr auto to(Args&&... args);
  template<template<class...> class C, class... Args>
  constexpr auto to(Args&&... args);

  // empty 视图
  template<class T>
    requires is_object_v<T>
  class empty_view;

  template<class T>
  constexpr bool enable_borrowed_range<empty_view<T>> = true;

  namespace views {
    template<class T>
    constexpr empty_view<T> empty{};
  }

  // single 视图
  template<move_constructible T>
    requires is_object_v<T>
  class single_view;

  namespace views {
    inline constexpr /* 未指定 */ single = /* 未指定 */;
  }

  template<bool Const, class T>
  using /*maybe-const*/ = conditional_t<Const, const T, T>; // 仅用于阐述

  // iota 视图
  template<weakly_incrementable W, semiregular Bound = unreachable_sentinel_t>
    requires /*weakly-equality-comparable-with*/<W, Bound> && copyable<W>
  class iota_view;

  template<class W, class Bound>
  constexpr bool enable_borrowed_range<iota_view<W, Bound>> = true;

  namespace views {
    inline constexpr /* 未指定 */ iota = /* 未指定 */;
  }

  // repeat 视图
  template<move_constructible T, semiregular Bound = unreachable_sentinel_t>
    requires         /* 见描述 */
  class repeat_view;

  namespace views {
    inline constexpr /* 未指定 */ repeat = /* 未指定 */;
  }

  // istream 视图
  template<movable Val, class CharT, class Traits = char_traits<CharT>>
    requires                /* 见描述 */
  class basic_istream_view; // 宿主实现
  template<class Val>
  using istream_view = basic_istream_view<Val, char>; // 宿主实现
  template<class Val>
  using wistream_view = basic_istream_view<Val, wchar_t>; // 宿主实现

  namespace views {
    template<class T>
    constexpr /* 未指定 */ istream = /* 未指定 */; // 宿主实现
  }

  // 范围适配器对象
  template<class D>
    requires is_class_v<D> && same_as<D, remove_cv_t<D>>
  class range_adaptor_closure
  {};

  // all 视图
  namespace views {
    inline constexpr /* 未指定 */ all = /* 未指定 */;

    template<viewable_range R>
    using all_t = decltype(all(declval<R>()));
  }

  // ref 视图
  template<range R>
    requires is_object_v<R>
  class ref_view;

  template<class T>
  constexpr bool enable_borrowed_range<ref_view<T>> = true;

  // owning 视图
  template<range R>
    requires /* 见描述 */
  class owning_view;

  template<class T>
  constexpr bool enable_borrowed_range<owning_view<T>> = enable_borrowed_range<T>;

  // as rvalue 视图
  template<view V>
    requires input_range<V>
  class as_rvalue_view;

  template<class T>
  constexpr bool enable_borrowed_range<as_rvalue_view<T>> = enable_borrowed_range<T>;

  namespace views {
    inline constexpr /* 未指定 */ as_rvalue = /* 未指定 */;
  }

  // filter 视图
  template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred>
    requires view<V> && is_object_v<Pred>
  class filter_view;

  namespace views {
    inline constexpr /* 未指定 */ filter = /* 未指定 */;
  }

  // transform 视图
  template<input_range V, move_constructible F>
    requires view<V> && is_object_v<F> && regular_invocable<F&, range_reference_t<V>> &&
             /*can-reference*/<invoke_result_t<F&, range_reference_t<V>>>
  class transform_view;

  namespace views {
    inline constexpr /* 未指定 */ transform = /* 未指定 */;
  }

  // take 视图
  template<view>
  class take_view;

  template<class T>
  constexpr bool enable_borrowed_range<take_view<T>> = enable_borrowed_range<T>;

  namespace views {
    inline constexpr /* 未指定 */ take = /* 未指定 */;
  }

  // take while 视图
  template<view V, class Pred>
    requires input_range<V> && is_object_v<Pred> &&
             indirect_unary_predicate<const Pred, iterator_t<V>>
  class take_while_view;

  namespace views {
    inline constexpr /* 未指定 */ take_while = /* 未指定 */;
  }

  // drop 视图
  template<view V>
  class drop_view;

  template<class T>
  constexpr bool enable_borrowed_range<drop_view<T>> = enable_borrowed_range<T>;

  namespace views {
    inline constexpr /* 未指定 */ drop = /* 未指定 */;
  }

  // drop while 视图
  template<view V, class Pred>
    requires input_range<V> && is_object_v<Pred> &&
             indirect_unary_predicate<const Pred, iterator_t<V>>
  class drop_while_view;

  template<class T, class Pred>
  constexpr bool enable_borrowed_range<drop_while_view<T, Pred>> =
    enable_borrowed_range<T>;

  namespace views {
    inline constexpr /* 未指定 */ drop_while = /* 未指定 */;
  }

  // join 视图
  template<input_range V>
    requires view<V> && input_range<range_reference_t<V>>
  class join_view;

  namespace views {
    inline constexpr /* 未指定 */ join = /* 未指定 */;
  }

  // join with 视图
  template<input_range V, forward_range Pattern>
    requires /* 见描述 */
  class join_with_view;

  namespace views {
    inline constexpr /* 未指定 */ join_with = /* 未指定 */;
  }

  // lazy split 视图
  template<class R>
  concept /*tiny-range*/ = /* 见描述 */; // 仅用于阐述

  template<input_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>,
                                   iterator_t<Pattern>,
                                   ranges::equal_to> &&
             (forward_range<V> || /*tiny-range*/<Pattern>)
  class lazy_split_view;

  // split 视图
  template<forward_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to>
  class split_view;

  namespace views {
    inline constexpr /* 未指定 */ lazy_split = /* 未指定 */;
    inline constexpr /* 未指定 */ split      = /* 未指定 */;
  }

  // concat 视图
  template<input_range... Views>
    requires /* 见描述 */
  class concat_view;

  namespace views {
    inline constexpr /* 未指定 */ concat = /* 未指定 */;
  }

  // counted 视图
  namespace views {
    inline constexpr /* 未指定 */ counted = /* 未指定 */;
  }

  // common 视图
  template<view V>
    requires(!common_range<V> && copyable<iterator_t<V>>)
  class common_view;

  template<class T>
  constexpr bool enable_borrowed_range<common_view<T>> = enable_borrowed_range<T>;

  namespace views {
    inline constexpr /* 未指定 */ common = /* 未指定 */;
  }

  // reverse 视图
  template<view V>
    requires bidirectional_range<V>
  class reverse_view;

  template<class T>
  constexpr bool enable_borrowed_range<reverse_view<T>> = enable_borrowed_range<T>;

  namespace views {
    inline constexpr /* 未指定 */ reverse = /* 未指定 */;
  }

  // as const 视图
  template<input_range R>
  constexpr auto& /*possibly-const-range*/(R& r) noexcept
  { // 仅用于阐述
    if constexpr (constant_range<const R> && !constant_range<R>) {
      return const_cast<const R&>(r);
    } else {
      return r;
    }
  }

  template<view V>
    requires input_range<V>
  class as_const_view;

  template<class T>
  constexpr bool enable_borrowed_range<as_const_view<T>> = enable_borrowed_range<T>;

  namespace views {
    inline constexpr /* 未指定 */ as_const = /* 未指定 */;
  }

  // elements 视图
  template<input_range V, size_t N>
    requires /* 见描述 */
  class elements_view;

  template<class T, size_t N>
  constexpr bool enable_borrowed_range<elements_view<T, N>> = enable_borrowed_range<T>;

  template<class R>
  using keys_view = elements_view<R, 0>;
  template<class R>
  using values_view = elements_view<R, 1>;

  namespace views {
    template<size_t N>
    constexpr /* 未指定 */ elements = /* 未指定 */;
    inline constexpr auto keys           = elements<0>;
    inline constexpr auto values         = elements<1>;
  }

  // enumerate 视图
  template<view V>
    requires /* 见描述 */
  class enumerate_view;

  template<class View>
  constexpr bool enable_borrowed_range<enumerate_view<View>> =
    enable_borrowed_range<View>;

  namespace views {
    inline constexpr /* 未指定 */ enumerate = /* 未指定 */;
  }

  // zip 视图
  template<input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0)
  class zip_view;

  template<class... Views>
  constexpr bool enable_borrowed_range<zip_view<Views...>> =
    (enable_borrowed_range<Views> && ...);

  namespace views {
    inline constexpr /* 未指定 */ zip = /* 未指定 */;
  }

  // zip transform 视图
  template<move_constructible F, input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0) && is_object_v<F> &&
            regular_invocable<F&, range_reference_t<Views>...> &&
            /*can-reference*/<invoke_result_t<F&, range_reference_t<Views>...>>
  class zip_transform_view;

  namespace views {
    inline constexpr /* 未指定 */ zip_transform = /* 未指定 */;
  }

  // adjacent 视图
  template<forward_range V, size_t N>
    requires view<V> && (N > 0)
  class adjacent_view;

  template<class V, size_t N>
  constexpr bool enable_borrowed_range<adjacent_view<V, N>> = enable_borrowed_range<V>;

  namespace views {
    template<size_t N>
    constexpr /* 未指定 */ adjacent = /* 未指定 */;
    inline constexpr auto pairwise       = adjacent<2>;
  }

  // adjacent transform 视图
  template<forward_range V, move_constructible F, size_t N>
    requires /* 见描述 */
  class adjacent_transform_view;

  namespace views {
    template<size_t N>
    constexpr /* 未指定 */ adjacent_transform = /* 未指定 */;
    inline constexpr auto pairwise_transform = adjacent_transform<2>;
  }

  // chunk 视图
  template<view V>
    requires input_range<V>
  class chunk_view;

  template<view V>
    requires forward_range<V>
  class chunk_view<V>;

  template<class V>
  constexpr bool enable_borrowed_range<chunk_view<V>> =
    forward_range<V> && enable_borrowed_range<V>;

  namespace views {
    inline constexpr /* 未指定 */ chunk = /* 未指定 */;
  }

  // slide 视图
  template<forward_range V>
    requires view<V>
  class slide_view;

  template<class V>
  constexpr bool enable_borrowed_range<slide_view<V>> = enable_borrowed_range<V>;

  namespace views {
    inline constexpr /* 未指定 */ slide = /* 未指定 */;
  }

  // chunk by 视图
  template<forward_range V, indirect_binary_predicate<iterator_t<V>, iterator_t<V>> Pred>
    requires view<V> && is_object_v<Pred>
  class chunk_by_view;

  namespace views {
    inline constexpr /* 未指定 */ chunk_by = /* 未指定 */;
  }

  // stride 视图
  template<input_range V>
    requires view<V>
  class stride_view;

  template<class V>
  constexpr bool enable_borrowed_range<stride_view<V>> = enable_borrowed_range<V>;

  namespace views {
    inline constexpr /* 未指定 */ stride = /* 未指定 */;
  }

  // cartesian product 视图
  template<input_range First, forward_range... Vs>
    requires(view<First> && ... && view<Vs>)
  class cartesian_product_view;

  namespace views {
    inline constexpr /* 未指定 */ cartesian_product = /* 未指定 */;
  }

  // cache latest 视图
  template<input_range V>
    requires view<V>
  class cache_latest_view;

  namespace views {
    inline constexpr /* 未指定 */ cache_latest = /* 未指定 */;
  }

  // to input 视图
  template<input_range V>
    requires view<V>
  class to_input_view;

  template<class V>
  constexpr bool enable_borrowed_range<to_input_view<V>> = enable_borrowed_range<V>;

  namespace views {
    inline constexpr /* 未指定 */ to_input = /* 未指定 */;
  }
}

namespace std {
  namespace views = ranges::views;

  template<class T>
  struct tuple_size;
  template<size_t I, class T>
  struct tuple_element;

  template<class I, class S, ranges::subrange_kind K>
  struct tuple_size<ranges::subrange<I, S, K>> : integral_constant<size_t, 2>
  {};
  template<class I, class S, ranges::subrange_kind K>
  struct tuple_element<0, ranges::subrange<I, S, K>>
  {
    using type = I;
  };
  template<class I, class S, ranges::subrange_kind K>
  struct tuple_element<1, ranges::subrange<I, S, K>>
  {
    using type = S;
  };
  template<class I, class S, ranges::subrange_kind K>
  struct tuple_element<0, const ranges::subrange<I, S, K>>
  {
    using type = I;
  };
  template<class I, class S, ranges::subrange_kind K>
  struct tuple_element<1, const ranges::subrange<I, S, K>>
  {
    using type = S;
  };

  struct from_range_t
  {
    explicit from_range_t() = default;
  };
  inline constexpr from_range_t from_range{};
}

概念 range

namespace std::ranges {
  template<class T>
  concept range = requires(T& t) {
    ranges::begin(t); // 有时保持相等性（见描述）
    ranges::end(t);
  };
}

概念 borrowed_range

namespace std::ranges {
  template<class T>
  concept borrowed_range =
    range<T> && (is_lvalue_reference_v<T> || enable_borrowed_range<remove_cvref_t<T>>);
}

概念 approximately_sized_range

namespace std::ranges {
  template<class T>
  concept approximately_sized_range = range<T> && requires(T& t) {
    ranges::reserve_hint(t);
  };
}

概念 sized_range

namespace std::ranges {
  template<class T>
  concept sized_range = approximately_sized_range<T> && requires(T& t) {
    ranges::size(t);
  };
}

概念 view

namespace std::ranges {
  template<class T>
  constexpr bool /*is-derived-from-view-interface*/ =
    /* 见描述 */; // 仅用于阐述
  template<class T>
  constexpr bool enable_view =
    derived_from<T, view_base> || /*is-derived-from-view-interface*/<T>;

  template<class T>
  concept view = range<T> && movable<T> && enable_view<T>;
}

概念 output_range

namespace std::ranges {
  template<class R, class T>
  concept output_range = range<R> && output_iterator<iterator_t<R>, T>;
}

概念 input_range

namespace std::ranges {
  template<class T>
  concept input_range = range<T> && input_iterator<iterator_t<T>>;
}

概念 forward_range

namespace std::ranges {
  template<class T>
  concept forward_range = input_range<T> && forward_iterator<iterator_t<T>>;
}

概念 bidirectional_range

namespace std::ranges {
  template<class T>
  concept bidirectional_range = forward_range<T> && bidirectional_iterator<iterator_t<T>>;
}

概念 random_access_range

namespace std::ranges {
  template<class T>
  concept random_access_range =
    bidirectional_range<T> && random_access_iterator<iterator_t<T>>;
}

概念 contiguous_range

namespace std::ranges {
  template<class T>
  concept contiguous_range =
    random_access_range<T> && contiguous_iterator<iterator_t<T>> && requires(T& t) {
      {
        ranges::data(t)
      } -> same_as<add_pointer_t<range_reference_t<T>>>;
    };
}

概念 common_range

namespace std::ranges {
  template<class T>
  concept common_range = range<T> && same_as<iterator_t<T>, sentinel_t<T>>;
}

概念 viewable_range

namespace std::ranges {
  template<class T>
  concept viewable_range =
    range<T> && ((view<remove_cvref_t<T>> && constructible_from<remove_cvref_t<T>, T>) ||
                 (!view<remove_cvref_t<T>> &&
                  (is_lvalue_reference_v<T> ||
                   (movable<remove_reference_t<T>> && !/*is-initializer-list*/<T>))));
}

概念 constant_range

namespace std::ranges {
  template<class T>
  concept constant_range = input_range<T> && /*constant-iterator*/<iterator_t<T>>;
}

辅助概念

注解：这个部分中的概念的仅用于阐述，他们不是接口的一部分。 

namespace std::ranges { // 未指定，仅用于名字查找
  template<class R>
  concept /*simple-view*/ = // 仅用于阐述
    view<R> && range<const R> && same_as<iterator_t<R>, iterator_t<const R>> &&
    same_as<sentinel_t<R>, sentinel_t<const R>>;

  template<class I>
  concept /*has-arrow*/ = // 仅用于阐述
    input_iterator<I> && (is_pointer_v<I> || requires(I i) { i.operator->(); });

  template<class T, class U>
  concept /*different-from*/ = // 仅用于阐述
    !same_as<remove_cvref_t<T>, remove_cvref_t<U>>;

  template<class R>
  concept /*range-with-movable-references*/ = // 仅用于阐述
    input_range<R> && move_constructible<range_reference_t<R>> &&
    move_constructible<range_rvalue_reference_t<R>>;

  template<class R>
  constexpr bool /*is-initializer-list*/ = /* 见描述 */; // 仅用于阐述

  template<class T>
  constexpr auto
  /*as-const-pointer*/(const T* p) noexcept
  {
    return p;
  } // 仅用于阐述
}

类模板 std::ranges::view_interface

namespace std::ranges {
  template<class D>
    requires is_class_v<D> && same_as<D, remove_cv_t<D>>
  class view_interface
  {
  private:
    constexpr D& /*derived*/() noexcept
    { // 仅用于阐述
      return static_cast<D&>(*this);
    }
    constexpr const D& /*derived*/() const noexcept
    { // 仅用于阐述
      return static_cast<const D&>(*this);
    }

  public:
    constexpr bool empty()
      requires sized_range<D> || forward_range<D>
    {
      if constexpr (sized_range<D>)
        return ranges::size(/*derived*/()) == 0;
      else
        return ranges::begin(/*derived*/()) == ranges::end(/*derived*/());
    }
    constexpr bool empty() const
      requires sized_range<const D> || forward_range<const D>
    {
      if constexpr (sized_range<const D>)
        return ranges::size(/*derived*/()) == 0;
      else
        return ranges::begin(/*derived*/()) == ranges::end(/*derived*/());
    }

    constexpr auto cbegin()
      requires input_range<D>
    {
      return ranges::cbegin(/*derived*/());
    }
    constexpr auto cbegin() const
      requires input_range<const D>
    {
      return ranges::cbegin(/*derived*/());
    }
    constexpr auto cend()
      requires input_range<D>
    {
      return ranges::cend(/*derived*/());
    }
    constexpr auto cend() const
      requires input_range<const D>
    {
      return ranges::cend(/*derived*/());
    }

    constexpr explicit operator bool()
      requires requires { ranges::empty(/*derived*/()); }
    {
      return !ranges::empty(/*derived*/());
    }
    constexpr explicit operator bool() const
      requires requires { ranges::empty(/*derived*/()); }
    {
      return !ranges::empty(/*derived*/());
    }

    constexpr auto data()
      requires contiguous_iterator<iterator_t<D>>
    {
      return to_address(ranges::begin(/*derived*/()));
    }
    constexpr auto data() const
      requires range<const D> && contiguous_iterator<iterator_t<const D>>
    {
      return to_address(ranges::begin(/*derived*/()));
    }

    constexpr auto size()
      requires forward_range<D> && sized_sentinel_for<sentinel_t<D>, iterator_t<D>>
    {
      return /*to-unsigned-like*/(ranges::end(/*derived*/()) -
                                  ranges::begin(/*derived*/()));
    }
    constexpr auto size() const
      requires forward_range<const D> &&
               sized_sentinel_for<sentinel_t<const D>, iterator_t<const D>>
    {
      return /*to-unsigned-like*/(ranges::end(/*derived*/()) -
                                  ranges::begin(/*derived*/()));
    }

    constexpr decltype(auto) front()
      requires forward_range<D>;
    constexpr decltype(auto) front() const
      requires forward_range<const D>;

    constexpr decltype(auto) back()
      requires bidirectional_range<D> && common_range<D>;
    constexpr decltype(auto) back() const
      requires bidirectional_range<const D> && common_range<const D>;

    template<random_access_range R = D>
    constexpr decltype(auto) operator[](range_difference_t<R> n)
    {
      return ranges::begin(/*derived*/())[n];
    }
    template<random_access_range R = const D>
    constexpr decltype(auto) operator[](range_difference_t<R> n) const
    {
      return ranges::begin(/*derived*/())[n];
    }
  };
}

类模板 std::ranges::subrange

namespace std::ranges {
  template<class From, class To>
  concept /*uses-nonqualification-pointer-conversion*/ = // 仅用于阐述
    is_pointer_v<From> && is_pointer_v<To> &&
    !convertible_to<remove_pointer_t<From> (*)[], remove_pointer_t<To> (*)[]>;

  template<class From, class To>
  concept /*convertible-to-non-slicing*/ = // 仅用于阐述
    convertible_to<From, To> &&
    !/*uses-nonqualification-pointer-conversion*/<decay_t<From>, decay_t<To>>;

  template<class T, class U, class V>
  concept /*pair-like-convertible-from*/ = // 仅用于阐述
    !range<T> && !is_reference_v<T> && /*pair-like*/<T> && constructible_from<T, U, V> &&
    /*convertible-to-non-slicing*/<U, tuple_element_t<0, T>> &&
    convertible_to<V, tuple_element_t<1, T>>;

  template<input_or_output_iterator I,
           sentinel_for<I> S = I,
           subrange_kind K =
             sized_sentinel_for<S, I> ? subrange_kind::sized : subrange_kind::unsized>
    requires(K == subrange_kind::sized || !sized_sentinel_for<S, I>)
  class subrange : public view_interface<subrange<I, S, K>>
  {
  private:
    static constexpr bool /*StoreSize*/ = // 仅用于阐述
      K == subrange_kind::sized && !sized_sentinel_for<S, I>;
    I /*begin_*/ = I(); // 仅用于阐述
    S /*end_*/   = S(); // 仅用于阐述
    /*make-unsigned-like-t*/<iter_difference_t<I>> /*size_*/ =
      0; // 仅用于阐述；仅当 StoreSize 为 true 时出现
  public:
    subrange()
      requires default_initializable<I>
    = default;

    constexpr subrange(/*convertible-to-non-slicing*/<I> auto i, S s)
      requires(!/*StoreSize*/);

    constexpr subrange(/*convertible-to-non-slicing*/<I> auto i,
                       S s,
                       /*make-unsigned-like-t*/<iter_difference_t<I>> n)
      requires(K == subrange_kind::sized);

    template</*different-from*/<subrange> R>
      requires borrowed_range<R> && /*convertible-to-non-slicing*/<iterator_t<R>, I> &&
               convertible_to<sentinel_t<R>, S>
               constexpr subrange(R&& r)
                 requires(!/*StoreSize*/ || sized_range<R>);

    template<borrowed_range R>
      requires /*convertible-to-non-slicing*/<iterator_t<R>, I> &&
               convertible_to<sentinel_t<R>, S>
               constexpr subrange(R&& r, /*make-unsigned-like-t*/<iter_difference_t<I>> n)
                 requires(K == subrange_kind::sized)
      : subrange{ ranges::begin(r), ranges::end(r), n }
    {
    }

    template</*different-from*/<subrange> PairLike>
      requires /*pair-like-convertible-from*/<PairLike, const I&, const S&>
    constexpr operator PairLike() const;

    constexpr I begin() const
      requires copyable<I>;
    constexpr I begin()
      requires(!copyable<I>);
    constexpr S end() const;

    constexpr bool empty() const;
    constexpr /*make-unsigned-like-t*/<iter_difference_t<I>> size() const
      requires(K == subrange_kind::sized);

    constexpr subrange next(iter_difference_t<I> n = 1) const&
      requires forward_iterator<I>;
    constexpr subrange next(iter_difference_t<I> n = 1) &&;
    constexpr subrange prev(iter_difference_t<I> n = 1) const
      requires bidirectional_iterator<I>;
    constexpr subrange& advance(iter_difference_t<I> n);
  };

  template<input_or_output_iterator I, sentinel_for<I> S>
  subrange(I, S) -> subrange<I, S>;

  template<input_or_output_iterator I, sentinel_for<I> S>
  subrange(I, S, /*make-unsigned-like-t*/<iter_difference_t<I>>)
    -> subrange<I, S, subrange_kind::sized>;

  template<borrowed_range R>
  subrange(R&&)
    -> subrange<iterator_t<R>,
                sentinel_t<R>,
                (sized_range<R> || sized_sentinel_for<sentinel_t<R>, iterator_t<R>>)
                  ? subrange_kind::sized
                  : subrange_kind::unsized>;

  template<borrowed_range R>
  subrange(R&&, /*make-unsigned-like-t*/<range_difference_t<R>>)
    -> subrange<iterator_t<R>, sentinel_t<R>, subrange_kind::sized>;
}

类 std::ranges::dangling

namespace std::ranges {
  struct dangling
  {
    constexpr dangling() noexcept = default;
    constexpr dangling(auto&&...) noexcept {}
  };
}

累 std::ranges::elements_of

namespace std::ranges {
  template<range R, class Allocator = allocator<byte>>
  struct elements_of
  {
    [[no_unique_address]] R range;
    [[no_unique_address]] Allocator allocator = Allocator();
  };

  template<class R, class Allocator = allocator<byte>>
  elements_of(R&&, Allocator = Allocator()) -> elements_of<R&&, Allocator>;
}

类模板 std::ranges::empty_view

namespace std::ranges {
  template<class T>
    requires is_object_v<T>
  class empty_view : public view_interface<empty_view<T>>
  {
  public:
    static constexpr T* begin() noexcept { return nullptr; }
    static constexpr T* end() noexcept { return nullptr; }
    static constexpr T* data() noexcept { return nullptr; }
    static constexpr size_t size() noexcept { return 0; }
    static constexpr bool empty() noexcept { return true; }
  };
}

类模板 std::ranges::single_view

namespace std::ranges {
  template<move_constructible T>
    requires is_object_v<T>
  class single_view : public view_interface<single_view<T>>
  {
  private:
    /*movable-box*/<T> /*value_*/; // 仅用于阐述

  public:
    single_view()
      requires default_initializable<T>
    = default;
    constexpr explicit single_view(const T& t)
      requires copy_constructible<T>;
    constexpr explicit single_view(T&& t);
    template<class... Args>
      requires constructible_from<T, Args...>
    constexpr explicit single_view(in_place_t, Args&&... args);

    constexpr T* begin() noexcept;
    constexpr const T* begin() const noexcept;
    constexpr T* end() noexcept;
    constexpr const T* end() const noexcept;
    static constexpr bool empty() noexcept;
    static constexpr size_t size() noexcept;
    constexpr T* data() noexcept;
    constexpr const T* data() const noexcept;
  };

  template<class T>
  single_view(T) -> single_view<T>;
}

类模板 std::ranges::iota_view

namespace std::ranges {
  template<class I>
  concept /*decrementable*/ = /* 见描述 */; // 仅用于阐述

  template<class I>
  concept /*advanceable*/ = /* 见描述 */; // 仅用于阐述

  template<weakly_incrementable W, semiregular Bound = unreachable_sentinel_t>
    requires /*weakly-equality-comparable-with*/<W, Bound> && copyable<W>
  class iota_view : public view_interface<iota_view<W, Bound>>
  {
  private:
    // 类 iota_view::iterator
    struct /*iterator*/; // 仅用于阐述

    // 类 iota_view::sentinel
    struct /*sentinel*/; // 仅用于阐述

    W /*value_*/     = W();     // 仅用于阐述
    Bound /*bound_*/ = Bound(); // 仅用于阐述

  public:
    iota_view()
      requires default_initializable<W>
    = default;
    constexpr explicit iota_view(W value);
    constexpr explicit iota_view(type_identity_t<W> value, type_identity_t<Bound> bound);
    constexpr explicit iota_view(/*iterator*/ first, /* 见描述 */ last);

    constexpr /*iterator*/ begin() const;
    constexpr auto end() const;
    constexpr /*iterator*/ end() const
      requires same_as<W, Bound>;

    constexpr bool empty() const;
    constexpr auto size() const
      requires /* 见描述 */;
  };

  template<class W, class Bound>
    requires(!/*is-integer-like*/<W> || !/*is-integer-like*/<Bound> ||
             (/*is-signed-integer-like*/<W> == /*is-signed-integer-like*/<Bound>))
  iota_view(W, Bound) -> iota_view<W, Bound>;
}

类模板 std::ranges::iota_view::iterator

namespace std::ranges {
  template<weakly_incrementable W, semiregular Bound>
    requires /*weakly-equality-comparable-with*/<W, Bound> && copyable<W>
  struct iota_view<W, Bound>::/*iterator*/
  {
  private:
    W /*value_*/ = W(); // 仅用于阐述

  public:
    using iterator_concept = /* 见描述 */;
    using iterator_category =
      input_iterator_tag; // 仅当 W 实现 incrementable 且
                          // IOTA-DIFF-T(W) 是整数类型时提供
    using value_type      = W;
    using difference_type = /*IOTA-DIFF-T*/(W);

    /*iterator*/()
      requires default_initializable<W>
    = default;
    constexpr explicit /*iterator*/(W value);

    constexpr W operator*() const noexcept(is_nothrow_copy_constructible_v<W>);

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires incrementable<W>;

    constexpr /*iterator*/& operator--()
      requires /*decrementable*/<W>;
    constexpr /*iterator*/ operator--(int)
      requires /*decrementable*/<W>;

    constexpr /*iterator*/& operator+=(difference_type n)
      requires /*advanceable*/<W>;
    constexpr /*iterator*/& operator-=(difference_type n)
      requires /*advanceable*/<W>;
    constexpr W operator[](difference_type n) const
      requires /*advanceable*/<W>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires equality_comparable<W>;

    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires totally_ordered<W>;
    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires totally_ordered<W>;
    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires totally_ordered<W>;
    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires totally_ordered<W>;
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires totally_ordered<W> && three_way_comparable<W>;

    friend constexpr /*iterator*/ operator+(/*iterator*/ i, difference_type n)
      requires /*advanceable*/<W>;
    friend constexpr /*iterator*/ operator+(difference_type n, /*iterator*/ i)
      requires /*advanceable*/<W>;

    friend constexpr /*iterator*/ operator-(/*iterator*/ i, difference_type n)
      requires /*advanceable*/<W>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires /*advanceable*/<W>;
  };
}

类模板 std::ranges::iota_view::sentinel

namespace std::ranges {
  template<weakly_incrementable W, semiregular Bound>
    requires /*weakly-equality-comparable-with*/<W, Bound> && copyable<W>
  struct iota_view<W, Bound>::/*sentinel*/
  {
  private:
    Bound /*bound_*/ = Bound(); // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr explicit /*sentinel*/(Bound bound);

    friend constexpr bool operator==(const /*iterator*/& x, const /*sentinel*/& y);

    friend constexpr iter_difference_t<W> operator-(const /*iterator*/& x,
                                                    const /*sentinel*/& y)
      requires sized_sentinel_for<Bound, W>;
    friend constexpr iter_difference_t<W> operator-(const /*sentinel*/& x,
                                                    const /*iterator*/& y)
      requires sized_sentinel_for<Bound, W>;
  };
}

类模板 std::ranges::repeat_view

namespace std::ranges {
  template<class T>
  concept /*integer-like-with-usable-difference-type*/ = // 仅用于阐述
    /*is-signed-integer-like*/<T> || (/*is-integer-like*/<T> && weakly_incrementable<T>);

  template<move_constructible T, semiregular Bound = unreachable_sentinel_t>
    requires(is_object_v<T> && same_as<T, remove_cv_t<T>> &&
             (/*integer-like-with-usable-difference-type*/<Bound> ||
              same_as<Bound, unreachable_sentinel_t>))
  class repeat_view : public view_interface<repeat_view<T, Bound>>
  {
  private:
    // class repeat_view::iterator
    struct /*iterator*/; // 仅用于阐述

    /*movable-box*/<T> /*value_*/; // 仅用于阐述
    Bound /*bound_*/ = Bound();    // 仅用于阐述

  public:
    repeat_view()
      requires default_initializable<T>
    = default;

    constexpr explicit repeat_view(const T& value, Bound bound = Bound())
      requires copy_constructible<T>;
    constexpr explicit repeat_view(T&& value, Bound bound = Bound());
    template<class... TArgs, class... BoundArgs>
      requires constructible_from<T, TArgs...> && constructible_from<Bound, BoundArgs...>
    constexpr explicit repeat_view(piecewise_construct_t,
                                   tuple<TArgs...> value_args,
                                   tuple<BoundArgs...> bound_args = tuple<>{});

    constexpr /*iterator*/ begin() const;
    constexpr /*iterator*/ end() const
      requires(!same_as<Bound, unreachable_sentinel_t>);
    constexpr unreachable_sentinel_t end() const noexcept;

    constexpr auto size() const
      requires(!same_as<Bound, unreachable_sentinel_t>);
  };

  template<class T, class Bound = unreachable_sentinel_t>
  repeat_view(T, Bound = Bound()) -> repeat_view<T, Bound>;
}

类模板 std::ranges::repeat_view::iterator

namespace std::ranges {
  template<move_constructible T, semiregular Bound>
    requires(is_object_v<T> && same_as<T, remove_cv_t<T>> &&
             (/*integer-like-with-usable-difference-type*/<Bound> ||
              same_as<Bound, unreachable_sentinel_t>))
  class repeat_view<T, Bound>::/*iterator*/
  {
  private:
    using /*index-type*/ = // 仅用于阐述
      conditional_t<same_as<Bound, unreachable_sentinel_t>, ptrdiff_t, Bound>;
    const T* /*value_*/         = nullptr;          // 仅用于阐述
    /*index-type*/ /*current_*/ = /*index-type*/(); // 仅用于阐述

    constexpr explicit /*iterator*/(
      const T* value,
      /*index-type*/ b = /*index-type*/()); // 仅用于阐述

  public:
    using iterator_concept  = random_access_iterator_tag;
    using iterator_category = random_access_iterator_tag;
    using value_type        = T;
    using difference_type   = /* 见描述 */;

    /*iterator*/()          = default;

    constexpr const T& operator*() const noexcept;

    constexpr /*iterator*/& operator++();
    constexpr /*iterator*/ operator++(int);

    constexpr /*iterator*/& operator--();
    constexpr /*iterator*/ operator--(int);

    constexpr /*iterator*/& operator+=(difference_type n);
    constexpr /*iterator*/& operator-=(difference_type n);
    constexpr const T& operator[](difference_type n) const noexcept;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y);
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y);

    friend constexpr /*iterator*/ operator+(/*iterator*/ i, difference_type n);
    friend constexpr /*iterator*/ operator+(difference_type n, /*iterator*/ i);

    friend constexpr /*iterator*/ operator-(/*iterator*/ i, difference_type n);
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y);
  };
}

类模板 std::ranges::basic_istream_view

namespace std::ranges {
  template<class Val, class CharT, class Traits>
  concept /*stream-extractable*/ = // 仅用于阐述
    requires(basic_istream<CharT, Traits>& is, Val& t) { is >> t; };

  template<movable Val, class CharT, class Traits = char_traits<CharT>>
    requires default_initializable<Val> && /*stream-extractable*/<Val, CharT, Traits>
  class basic_istream_view : public view_interface<basic_istream_view<Val, CharT, Traits>>
  {
  public:
    constexpr explicit basic_istream_view(basic_istream<CharT, Traits>& stream);

    constexpr auto begin()
    {
      */*stream_*/ >> /*value_*/;
      return /*iterator*/{ *this };
    }

    constexpr default_sentinel_t end() const noexcept;

  private:
    // 类 basic_istream_view::iterator
    struct /*iterator*/;                       // 仅用于阐述
    basic_istream<CharT, Traits>* /*stream_*/; // 仅用于阐述
    Val /*value_*/ = Val();                    // 仅用于阐述
  };
}

类模板 std::ranges::basic_istream_view::iterator

namespace std::ranges {
  template<movable Val, class CharT, class Traits>
    requires default_initializable<Val> && /*stream-extractable*/<Val, CharT, Traits>
  class basic_istream_view<Val, CharT, Traits>::/*iterator*/
  {
  public:
    using iterator_concept = input_iterator_tag;
    using difference_type  = ptrdiff_t;
    using value_type       = Val;

    constexpr explicit /*iterator*/(basic_istream_view& parent) noexcept;

    /*iterator*/(const /*iterator*/&)            = delete;
    /*iterator*/(/*iterator*/&&)                 = default;

    /*iterator*/& operator=(const /*iterator*/&) = delete;
    /*iterator*/& operator=(/*iterator*/&&)      = default;

    /*iterator*/& operator++();
    void operator++(int);

    Val& operator*() const;

    friend bool operator==(const /*iterator*/& x, default_sentinel_t);

  private:
    basic_istream_view* /*parent_*/; // 仅用于阐述
  };
}

类模板 std::ranges::ref_view

namespace std::ranges {
  template<range R>
    requires is_object_v<R>
  class ref_view : public view_interface<ref_view<R>>
  {
  private:
    R* /*r_*/; // 仅用于阐述

  public:
    template</*different-from*/<ref_view> T>
      requires /* 见描述 */
      constexpr
    ref_view(T&& t);

    constexpr R& base() const { return */*r_*/; }

    constexpr iterator_t<R> begin() const { return ranges::begin(*/*r_*/); }
    constexpr sentinel_t<R> end() const { return ranges::end(*/*r_*/); }

    constexpr bool empty() const
      requires requires { ranges::empty(*/*r_*/); }
    {
      return ranges::empty(*/*r_*/);
    }

    constexpr auto size() const
      requires sized_range<R>
    {
      return ranges::size(*/*r_*/);
    }

    constexpr auto reserve_hint() const
      requires approximately_sized_range<R>
    {
      return ranges::reserve_hint(*/*r_*/);
    }

    constexpr auto data() const
      requires contiguous_range<R>
    {
      return ranges::data(*/*r_*/);
    }
  };

  template<class R>
  ref_view(R&) -> ref_view<R>;
}

类模板 std::ranges::owning_view

namespace std::ranges {
  template<range R>
    requires movable<R> && (!/*is-initializer-list*/<R>)
  class owning_view : public view_interface<owning_view<R>>
  {
  private:
    R /*r_*/ = R(); // 仅用于阐述

  public:
    owning_view()
      requires default_initializable<R>
    = default;
    constexpr owning_view(R&& t);

    owning_view(owning_view&&)            = default;
    owning_view& operator=(owning_view&&) = default;

    constexpr R& base() & noexcept { return /*r_*/; }
    constexpr const R& base() const& noexcept { return /*r_*/; }
    constexpr R&& base() && noexcept { return std::move(/*r_*/); }
    constexpr const R&& base() const&& noexcept { return std::move(/*r_*/); }

    constexpr iterator_t<R> begin() { return ranges::begin(/*r_*/); }
    constexpr sentinel_t<R> end() { return ranges::end(/*r_*/); }

    constexpr auto begin() const
      requires range<const R>
    {
      return ranges::begin(/*r_*/);
    }
    constexpr auto end() const
      requires range<const R>
    {
      return ranges::end(/*r_*/);
    }

    constexpr bool empty()
      requires requires { ranges::empty(/*r_*/); }
    {
      return ranges::empty(/*r_*/);
    }
    constexpr bool empty() const
      requires requires { ranges::empty(/*r_*/); }
    {
      return ranges::empty(/*r_*/);
    }

    constexpr auto size()
      requires sized_range<R>
    {
      return ranges::size(/*r_*/);
    }
    constexpr auto size() const
      requires sized_range<const R>
    {
      return ranges::size(/*r_*/);
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<R>
    {
      return ranges::reserve_hint(/*r_*/);
    }
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const R>
    {
      return ranges::reserve_hint(/*r_*/);
    }

    constexpr auto data()
      requires contiguous_range<R>
    {
      return ranges::data(/*r_*/);
    }
    constexpr auto data() const
      requires contiguous_range<const R>
    {
      return ranges::data(/*r_*/);
    }
  };
}

类模板 std::ranges::as_rvalue_view

namespace std::ranges {
  template<view V>
    requires input_range<V>
  class as_rvalue_view : public view_interface<as_rvalue_view<V>>
  {
    V /*base_*/ = V(); // 仅用于阐述

  public:
    as_rvalue_view()
      requires default_initializable<V>
    = default;
    constexpr explicit as_rvalue_view(V base);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      return move_iterator(ranges::begin(/*base_*/));
    }
    constexpr auto begin() const
      requires range<const V>
    {
      return move_iterator(ranges::begin(/*base_*/));
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (common_range<V>) {
        return move_iterator(ranges::end(/*base_*/));
      } else {
        return move_sentinel(ranges::end(/*base_*/));
      }
    }
    constexpr auto end() const
      requires range<const V>
    {
      if constexpr (common_range<const V>) {
        return move_iterator(ranges::end(/*base_*/));
      } else {
        return move_sentinel(ranges::end(/*base_*/));
      }
    }

    constexpr auto size()
      requires sized_range<V>
    {
      return ranges::size(/*base_*/);
    }
    constexpr auto size() const
      requires sized_range<const V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
  };

  template<class R>
  as_rvalue_view(R&&) -> as_rvalue_view<views::all_t<R>>;
}

类模板 std::ranges::filter_view

namespace std::ranges {
  template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred>
    requires view<V> && is_object_v<Pred>
  class filter_view : public view_interface<filter_view<V, Pred>>
  {
  private:
    V /*base_*/ = V();               // 仅用于阐述
    /*movable-box*/<Pred> /*pred_*/; // 仅用于阐述

    // 类 filter_view::iterator
    class /*iterator*/; // 仅用于阐述

    // 类 filter_view::sentinel
    class /*sentinel*/; // 仅用于阐述

  public:
    filter_view()
      requires default_initializable<V> && default_initializable<Pred>
    = default;
    constexpr explicit filter_view(V base, Pred pred);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr const Pred& pred() const;

    constexpr /*iterator*/ begin();
    constexpr auto end()
    {
      if constexpr (common_range<V>)
        return /*iterator*/{ *this, ranges::end(/*base_*/) };
      else
        return /*sentinel*/{ *this };
    }
  };

  template<class R, class Pred>
  filter_view(R&&, Pred) -> filter_view<views::all_t<R>, Pred>;
}

类模板 std::ranges::filter_view::iterator

namespace std::ranges {
  template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred>
    requires view<V> && is_object_v<Pred>
  class filter_view<V, Pred>::/*iterator*/
  {
  private:
    iterator_t<V> /*current_*/ = iterator_t<V>(); // 仅用于阐述
    filter_view* /*parent_*/   = nullptr;         // 仅用于阐述

  public:
    using iterator_concept  = /* 见描述 */;
    using iterator_category = /* 见描述 */; // 不总存在
    using value_type        = range_value_t<V>;
    using difference_type   = range_difference_t<V>;

    /*iterator*/()
      requires default_initializable<iterator_t<V>>
    = default;
    constexpr /*iterator*/(filter_view& parent, iterator_t<V> current);

    constexpr const iterator_t<V>& base() const& noexcept;
    constexpr iterator_t<V> base() &&;
    constexpr range_reference_t<V> operator*() const;
    constexpr iterator_t<V> operator->() const
      requires /*has-arrow*/<iterator_t<V>> && copyable<iterator_t<V>>;

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires forward_range<V>;

    constexpr /*iterator*/& operator--()
      requires bidirectional_range<V>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range<V>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires equality_comparable<iterator_t<V>>;

    friend constexpr range_rvalue_reference_t<V> iter_move(
      const /*iterator*/& i) noexcept(noexcept(ranges::iter_move(i./*current_*/)));

    friend constexpr void iter_swap(
      const /*iterator*/& x,
      const /*iterator*/& y) noexcept(noexcept(ranges::iter_swap(x./*current_*/,
                                                                 y./*current_*/)))
      requires indirectly_swappable<iterator_t<V>>;
  };
}

类模板 std::ranges::filter_view::sentinel

namespace std::ranges {
  template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred>
    requires view<V> && is_object_v<Pred>
  class filter_view<V, Pred>::/*sentinel*/
  {
  private:
    sentinel_t<V> /*end_*/ = sentinel_t<V>(); // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr explicit /*sentinel*/(filter_view& parent);

    constexpr sentinel_t<V> base() const;

    friend constexpr bool operator==(const /*iterator*/& x, const /*sentinel*/& y);
  };
}

类模板 std::ranges::transform_view

namespace std::ranges {
  template<input_range V, move_constructible F>
    requires view<V> && is_object_v<F> && regular_invocable<F&, range_reference_t<V>> &&
             /*can-reference*/<invoke_result_t<F&, range_reference_t<V>>>
  class transform_view : public view_interface<transform_view<V, F>>
  {
  private:
    // 类模板 transform_view::iterator
    template<bool>
    struct /*iterator*/; // 仅用于阐述

    // 类模板 transform_view::sentinel
    template<bool>
    struct /*sentinel*/; // 仅用于阐述

    V /*base_*/ = V();           // 仅用于阐述
    /*movable-box*/<F> /*fun_*/; // 仅用于阐述

  public:
    transform_view()
      requires default_initializable<V> && default_initializable<F>
    = default;
    constexpr explicit transform_view(V base, F fun);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr /*iterator*/<false> begin();
    constexpr /*iterator*/<true> begin() const
      requires range<const V> && regular_invocable<const F&, range_reference_t<const V>>;

    constexpr /*sentinel*/<false> end();
    constexpr /*iterator*/<false> end()
      requires common_range<V>;
    constexpr /*sentinel*/<true> end() const
      requires range<const V> && regular_invocable<const F&, range_reference_t<const V>>;
    constexpr /*iterator*/<true> end() const
      requires common_range<const V> &&
               regular_invocable<const F&, range_reference_t<const V>>;

    constexpr auto size()
      requires sized_range<V>
    {
      return ranges::size(/*base_*/);
    }
    constexpr auto size() const
      requires sized_range<const V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
  };

  template<class R, class F>
  transform_view(R&&, F) -> transform_view<views::all_t<R>, F>;
}

类模板 std::ranges::transform_view::iterator

namespace std::ranges {
  template<input_range V, move_constructible F>
    requires view<V> && is_object_v<F> && regular_invocable<F&, range_reference_t<V>> &&
             /*can-reference*/<invoke_result_t<F&, range_reference_t<V>>>
  template<bool Const>
  class transform_view<V, F>::/*iterator*/
  {
  private:
    using /*Parent*/ = /*maybe-const*/<Const, transform_view>;  // 仅用于阐述
    using /*Base*/   = /*maybe-const*/<Const, V>;               // 仅用于阐述
    iterator_t</*Base*/> /*current_*/ = iterator_t</*Base*/>(); // 仅用于阐述
    /*Parent*/* /*parent_*/           = nullptr;                // 仅用于阐述

  public:
    using iterator_concept  = /* 见描述 */;
    using iterator_category = /* 见描述 */; // 不总存在
    using value_type        = remove_cvref_t<
      invoke_result_t</*maybe-const*/<Const, F>&, range_reference_t</*Base*/>>>;
    using difference_type = range_difference_t</*Base*/>;

    /*iterator*/()
      requires default_initializable<iterator_t</*Base*/>>
    = default;
    constexpr /*iterator*/(/*Parent*/& parent, iterator_t</*Base*/> current);
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>>;

    constexpr const iterator_t</*Base*/>& base() const& noexcept;
    constexpr iterator_t</*Base*/> base() &&;

    constexpr decltype(auto) operator*() const
      noexcept(noexcept(invoke(*/*parent_*/->/*fun_*/, */*current_*/)))
    {
      return invoke(*/*parent_*/->/*fun_*/, */*current_*/);
    }

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires forward_range</*Base*/>;

    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;

    constexpr /*iterator*/& operator+=(difference_type n)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type n)
      requires random_access_range</*Base*/>;

    constexpr decltype(auto) operator[](difference_type n) const
      requires random_access_range</*Base*/>
    {
      return invoke(*/*parent_*/->/*fun_*/, /*current_*/[n]);
    }

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires equality_comparable<iterator_t</*Base*/>>;

    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/> && three_way_comparable<iterator_t</*Base*/>>
    ;

    friend constexpr /*iterator*/ operator+(/*iterator*/ i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type n, /*iterator*/ i)
      requires random_access_range</*Base*/>;

    friend constexpr /*iterator*/ operator-(/*iterator*/ i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires sized_sentinel_for<iterator_t</*Base*/>, iterator_t</*Base*/>>;
  };
}

类模板 std::ranges::transform_view::sentinel

namespace std::ranges {
  template<input_range V, move_constructible F>
    requires view<V> && is_object_v<F> && regular_invocable<F&, range_reference_t<V>> &&
             /*can-reference*/<invoke_result_t<F&, range_reference_t<V>>>
  template<bool Const>
  class transform_view<V, F>::/*sentinel*/
  {
  private:
    using /*Parent*/ = /*maybe-const*/<Const, transform_view>; // 仅用于阐述
    using /*Base*/   = /*maybe-const*/<Const, V>;              // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/ = sentinel_t</*Base*/>();    // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr explicit /*sentinel*/(sentinel_t</*Base*/> end);
    constexpr /*sentinel*/(/*sentinel*/<!Const> i)
      requires Const && convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    constexpr sentinel_t</*Base*/> base() const;

    template<bool OtherConst>
      requires sentinel_for<sentinel_t</*Base*/>,
                            iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for<sentinel_t</*Base*/>,
                                  iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, V>> operator-(
      const /*iterator*/<OtherConst>& x,
      const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for<sentinel_t</*Base*/>,
                                  iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, V>> operator-(
      const /*sentinel*/& y,
      const /*iterator*/<OtherConst>& x);
  };
}

类模板 std::ranges::take_view

namespace std::ranges {
  template<view V>
  class take_view : public view_interface<take_view<V>>
  {
  private:
    V /*base_*/                      = V(); // 仅用于阐述
    range_difference_t<V> /*count_*/ = 0;   // 仅用于阐述

    // 类模板 take_view::sentinel
    template<bool>
    class /*sentinel*/; // 仅用于阐述

  public:
    take_view()
      requires default_initializable<V>
    = default;
    constexpr explicit take_view(V base, range_difference_t<V> count);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (sized_range<V>) {
        if constexpr (random_access_range<V>) {
          return ranges::begin(/*base_*/);
        } else {
          auto sz = range_difference_t<V>(size());
          return counted_iterator(ranges::begin(/*base_*/), sz);
        }
      } else if constexpr (sized_sentinel_for<sentinel_t<V>, iterator_t<V>>) {
        auto it = ranges::begin(/*base_*/);
        auto sz = std::min(/*count_*/, ranges::end(/*base_*/) - it);
        return counted_iterator(std::move(it), sz);
      } else {
        return counted_iterator(ranges::begin(/*base_*/), /*count_*/);
      }
    }

    constexpr auto begin() const
      requires range<const V>
    {
      if constexpr (sized_range<const V>) {
        if constexpr (random_access_range<const V>) {
          return ranges::begin(/*base_*/);
        } else {
          auto sz = range_difference_t<const V>(size());
          return counted_iterator(ranges::begin(/*base_*/), sz);
        }
      } else if constexpr (sized_sentinel_for<sentinel_t<const V>, iterator_t<const V>>) {
        auto it = ranges::begin(/*base_*/);
        auto sz = std::min(/*count_*/, ranges::end(/*base_*/) - it);
        return counted_iterator(std::move(it), sz);
      } else {
        return counted_iterator(ranges::begin(/*base_*/), /*count_*/);
      }
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (sized_range<V>) {
        if constexpr (random_access_range<V>)
          return ranges::begin(/*base_*/) + range_difference_t<V>(size());
        else
          return default_sentinel;
      } else if constexpr (sized_sentinel_for<sentinel_t<V>, iterator_t<V>>) {
        return default_sentinel;
      } else {
        return /*sentinel*/<false>{ ranges::end(/*base_*/) };
      }
    }

    constexpr auto end() const
      requires range<const V>
    {
      if constexpr (sized_range<const V>) {
        if constexpr (random_access_range<const V>)
          return ranges::begin(/*base_*/) + range_difference_t<const V>(size());
        else
          return default_sentinel;
      } else if constexpr (sized_sentinel_for<sentinel_t<const V>, iterator_t<const V>>) {
        return default_sentinel;
      } else {
        return /*sentinel*/<true>{ ranges::end(/*base_*/) };
      }
    }

    constexpr auto size()
      requires sized_range<V>
    {
      auto n = ranges::size(/*base_*/);
      return ranges::min(n, static_cast<decltype(n)>(/*count_*/));
    }

    constexpr auto size() const
      requires sized_range<const V>
    {
      auto n = ranges::size(/*base_*/);
      return ranges::min(n, static_cast<decltype(n)>(/*count_*/));
    }

    constexpr auto reserve_hint()
    {
      if constexpr (approximately_sized_range<V>) {
        auto n = static_cast<range_difference_t<V>>(ranges::reserve_hint(/*base_*/));
        return /*to-unsigned-like*/(ranges::min(n, /*count_*/));
      }
      return /*to-unsigned-like*/(/*count_*/);
    }

    constexpr auto reserve_hint() const
    {
      if constexpr (approximately_sized_range<const V>) {
        auto n =
          static_cast<range_difference_t<const V>>(ranges::reserve_hint(/*base_*/));
        return /*to-unsigned-like*/(ranges::min(n, /*count_*/));
      }
      return /*to-unsigned-like*/(/*count_*/);
    }
  };

  template<class R>
  take_view(R&&, range_difference_t<R>) -> take_view<views::all_t<R>>;
}

类模板 std::ranges::take_view::sentinel

namespace std::ranges {
  template<view V>
  template<bool Const>
  class take_view<V>::/*sentinel*/
  {
  private:
    using /*Base*/ = /*maybe-const*/<Const, V>; // 仅用于阐述
    template<bool OtherConst>
    using /*CI*/ =
      counted_iterator<iterator_t</*maybe-const*/<OtherConst, V>>>; // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/ = sentinel_t</*Base*/>();         // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr explicit /*sentinel*/(sentinel_t</*Base*/> end);
    constexpr /*sentinel*/(/*sentinel*/<!Const> s)
      requires Const && convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    constexpr sentinel_t</*Base*/> base() const;

    friend constexpr bool operator==(const /*CI*/<Const>& y, const /*sentinel*/& x);

    template<bool OtherConst = !Const>
      requires sentinel_for<sentinel_t</*Base*/>,
                            iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr bool operator==(const /*CI*/<OtherConst>& y, const /*sentinel*/& x);
  };
}

类模板 std::ranges::take_while_view

namespace std::ranges {
  template<view V, class Pred>
    requires input_range<V> && is_object_v<Pred> &&
             indirect_unary_predicate<const Pred, iterator_t<V>>
  class take_while_view : public view_interface<take_while_view<V, Pred>>
  {
    // 类模板 take_while_view::sentinel
    template<bool>
    class /*sentinel*/; // 仅用于阐述

    V /*base_*/ = V();               // 仅用于阐述
    /*movable-box*/<Pred> /*pred_*/; // 仅用于阐述

  public:
    take_while_view()
      requires default_initializable<V> && default_initializable<Pred>
    = default;
    constexpr explicit take_while_view(V base, Pred pred);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr const Pred& pred() const;

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      return ranges::begin(/*base_*/);
    }

    constexpr auto begin() const
      requires range<const V> && indirect_unary_predicate<const Pred, iterator_t<const V>>
    {
      return ranges::begin(/*base_*/);
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      return /*sentinel*/<false>(ranges::end(/*base_*/), addressof(*/*pred_*/));
    }

    constexpr auto end() const
      requires range<const V> && indirect_unary_predicate<const Pred, iterator_t<const V>>
    {
      return /*sentinel*/<true>(ranges::end(/*base_*/), addressof(*/*pred_*/));
    }
  };

  template<class R, class Pred>
  take_while_view(R&&, Pred) -> take_while_view<views::all_t<R>, Pred>;
}

类模板 std::ranges::take_while_view::sentinel

namespace std::ranges {
  template<view V, class Pred>
    requires input_range<V> && is_object_v<Pred> &&
             indirect_unary_predicate<const Pred, iterator_t<V>>
  template<bool Const>
  class take_while_view<V, Pred>::/*sentinel*/
  {
    using /*Base*/                = /*maybe-const*/<Const, V>; // 仅用于阐述

    sentinel_t</*Base*/> /*end_*/ = sentinel_t</*Base*/>(); // 仅用于阐述
    const Pred* /*pred_*/         = nullptr;                // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr explicit /*sentinel*/(sentinel_t</*Base*/> end, const Pred* pred);
    constexpr /*sentinel*/(/*sentinel*/<!Const> s)
      requires Const && convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    constexpr sentinel_t</*Base*/> base() const { return /*end_*/; }

    friend constexpr bool operator==(const iterator_t</*Base*/>& x,
                                     const /*sentinel*/& y);

    template<bool OtherConst = !Const>
      requires sentinel_for<sentinel_t</*Base*/>,
                            iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr bool operator==(const iterator_t</*maybe-const*/<OtherConst, V>>& x,
                                     const /*sentinel*/& y);
  };
}

Class template std::ranges::drop_view

namespace std::ranges {
  template<view V>
  class drop_view : public view_interface<drop_view<V>>
  {
  public:
    drop_view()
      requires default_initializable<V>
    = default;
    constexpr explicit drop_view(V base, range_difference_t<V> count);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!(/*simple-view*/<V> && random_access_range<const V> &&
                 sized_range<const V>));
    constexpr auto begin() const
      requires random_access_range<const V> && sized_range<const V>;

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      return ranges::end(/*base_*/);
    }

    constexpr auto end() const
      requires range<const V>
    {
      return ranges::end(/*base_*/);
    }

    constexpr auto size()
      requires sized_range<V>
    {
      const auto s = ranges::size(/*base_*/);
      const auto c = static_cast<decltype(s)>(/*count_*/);
      return s < c ? 0 : s - c;
    }

    constexpr auto size() const
      requires sized_range<const V>
    {
      const auto s = ranges::size(/*base_*/);
      const auto c = static_cast<decltype(s)>(/*count_*/);
      return s < c ? 0 : s - c;
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>
    {
      const auto s = static_cast<range_difference_t<V>>(ranges::reserve_hint(/*base_*/));
      return /*to-unsigned-like*/(s < /*count_*/ ? 0 : s - /*count_*/);
    }

    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>
    {
      const auto s =
        static_cast<range_difference_t<const V>>(ranges::reserve_hint(/*base_*/));
      return /*to-unsigned-like*/(s < /*count_*/ ? 0 : s - /*count_*/);
    }

  private:
    V /*base_*/                      = V(); // 仅用于阐述
    range_difference_t<V> /*count_*/ = 0;   // 仅用于阐述
  };

  template<class R>
  drop_view(R&&, range_difference_t<R>) -> drop_view<views::all_t<R>>;
}

类模板 std::ranges::drop_while_view

namespace std::ranges {
  template<view V, class Pred>
    requires input_range<V> && is_object_v<Pred> &&
             indirect_unary_predicate<const Pred, iterator_t<V>>
  class drop_while_view : public view_interface<drop_while_view<V, Pred>>
  {
  public:
    drop_while_view()
      requires default_initializable<V> && default_initializable<Pred>
    = default;
    constexpr explicit drop_while_view(V base, Pred pred);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr const Pred& pred() const;

    constexpr auto begin();

    constexpr auto end() { return ranges::end(/*base_*/); }

  private:
    V /*base_*/ = V();               // 仅用于阐述
    /*movable-box*/<Pred> /*pred_*/; // 仅用于阐述
  };

  template<class R, class Pred>
  drop_while_view(R&&, Pred) -> drop_while_view<views::all_t<R>, Pred>;
}

类模板 std::ranges::join_view

namespace std::ranges {
  template<input_range V>
    requires view<V> && input_range<range_reference_t<V>>
  class join_view : public view_interface<join_view<V>>
  {
  private:
    using /*InnerRng*/ = range_reference_t<V>; // 仅用于阐述

    // 类模板 join_view::iterator
    template<bool Const>
    struct /*iterator*/; // 仅用于阐述

    // 类模板 join_view::sentinel
    template<bool Const>
    struct /*sentinel*/; // 仅用于阐述

    V /*base_*/ = V(); // 仅用于阐述

    /*non-propagating-cache*/<iterator_t<V>> /*outer_*/; // 仅用于阐述；仅当 !forward_range<V> 时存在
    /*non-propagating-cache*/<remove_cv_t</*InnerRng*/>>
      /*inner_*/; // 仅用于阐述；仅当 is_reference_v<InnerRng> 为 false 时存在

  public:
    join_view()
      requires default_initializable<V>
    = default;
    constexpr explicit join_view(V base);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
    {
      if constexpr (forward_range<V>) {
        constexpr bool use_const = /*simple-view*/<V> && is_reference_v</*InnerRng*/>;
        return /*iterator*/<use_const>{ *this, ranges::begin(/*base_*/) };
      } else {
        /*outer_*/ = ranges::begin(/*base_*/);
        return /*iterator*/<false>{ *this };
      }
    }

    constexpr auto begin() const
      requires forward_range<const V> && is_reference_v<range_reference_t<const V>> &&
               input_range<range_reference_t<const V>>
    {
      return /*iterator*/<true>{ *this, ranges::begin(/*base_*/) };
    }

    constexpr auto end()
    {
      if constexpr (forward_range<V> && is_reference_v</*InnerRng*/> &&
                    forward_range</*InnerRng*/> && common_range<V> &&
                    common_range</*InnerRng*/>)
        return /*iterator*/</*simple-view*/<V>>{ *this, ranges::end(/*base_*/) };
      else
        return /*sentinel*/</*simple-view*/<V>>{ *this };
    }

    constexpr auto end() const
      requires forward_range<const V> && is_reference_v<range_reference_t<const V>> &&
               input_range<range_reference_t<const V>>
    {
      if constexpr (forward_range<range_reference_t<const V>> && common_range<const V> &&
                    common_range<range_reference_t<const V>>)
        return /*iterator*/<true>{ *this, ranges::end(/*base_*/) };
      else
        return /*sentinel*/<true>{ *this };
    }
  };

  template<class R>
  explicit join_view(R&&) -> join_view<views::all_t<R>>;
}

类模板 std::ranges::join_view::iterator

namespace std::ranges {
  template<input_range V>
    requires view<V> && input_range<range_reference_t<V>>
  template<bool Const>
  struct join_view<V>::/*iterator*/
  {
  private:
    using /*Parent*/    = /*maybe-const*/<Const, join_view>;       // 仅用于阐述
    using /*Base*/      = /*maybe-const*/<Const, V>;               // 仅用于阐述
    using /*OuterIter*/ = iterator_t</*Base*/>;                    // 仅用于阐述
    using /*InnerIter*/ = iterator_t<range_reference_t</*Base*/>>; // 仅用于阐述

    static constexpr bool /*ref-is-glvalue*/ = // 仅用于阐述
      is_reference_v<range_reference_t</*Base*/>>;

    /*OuterIter*/ /*outer_*/ = /*OuterIter*/(); // 仅用于阐述；仅当 Base 实现 forward_range 时存在
    optional</*InnerIter*/> /*inner_*/;         // 仅用于阐述
    /*Parent*/* /*parent_*/ = nullptr;          // 仅用于阐述

    constexpr void /*satisfy*/(); // 仅用于阐述

    constexpr /*OuterIter*/& /*outer*/();             // 仅用于阐述
    constexpr const /*OuterIter*/& /*outer*/() const; // 仅用于阐述

    constexpr /*iterator*/(/*Parent*/& parent, /*OuterIter*/ outer)
      requires forward_range</*Base*/>; // 仅用于阐述
    constexpr explicit /*iterator*/(/*Parent*/& parent)
      requires(!forward_range</*Base*/>); // 仅用于阐述

  public:
    using iterator_concept  = /* 见描述 */;
    using iterator_category = /* 见描述 */; // 不总存在
    using value_type        = range_value_t<range_reference_t</*Base*/>>;
    using difference_type   = /* 见描述 */;

    /*iterator*/()          = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, /*OuterIter*/> &&
               convertible_to<iterator_t</*InnerRng*/>, /*InnerIter*/>;

    constexpr decltype(auto) operator*() const { return **/*inner_*/; }

    constexpr /*InnerIter*/ operator->() const
      requires /*has-arrow*/</*InnerIter*/> && copyable</*InnerIter*/>;

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires /*ref-is-glvalue*/
               && forward_range</*Base*/> && forward_range<range_reference_t</*Base*/>>;

    constexpr /*iterator*/& operator--()
      requires /*ref-is-glvalue*/ && bidirectional_range</*Base*/> &&
               bidirectional_range<range_reference_t</*Base*/>> &&
               common_range<range_reference_t</*Base*/>>;

    constexpr /*iterator*/ operator--(int)
      requires /*ref-is-glvalue*/ && bidirectional_range</*Base*/> &&
               bidirectional_range<range_reference_t</*Base*/>> &&
               common_range<range_reference_t</*Base*/>>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires /*ref-is-glvalue*/ && forward_range</*Base*/> &&
               equality_comparable<iterator_t<range_reference_t</*Base*/>>>;

    friend constexpr decltype(auto) iter_move(const /*iterator*/& i) noexcept(
      noexcept(ranges::iter_move(*i./*inner_*/)))
    {
      return ranges::iter_move(*i./*inner_*/);
    }

    friend constexpr void iter_swap(
      const /*iterator*/& x,
      const /*iterator*/& y) noexcept(noexcept(ranges::iter_swap(*x./*inner_*/,
                                                                 *y./*inner_*/)))
      requires indirectly_swappable</*InnerIter*/>;
  };
}

类模板 std::ranges::join_view::sentinel

namespace std::ranges {
  template<input_range V>
    requires view<V> && input_range<range_reference_t<V>>
  template<bool Const>
  struct join_view<V>::/*sentinel*/
  {
  private:
    using /*Parent*/              = /*maybe-const*/<Const, join_view>; // 仅用于阐述
    using /*Base*/                = /*maybe-const*/<Const, V>;         // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/ = sentinel_t</*Base*/>();            // 仅用于阐述

  public:
    /*sentinel*/() = default;

    constexpr explicit /*sentinel*/(/*Parent*/& parent);
    constexpr /*sentinel*/(/*sentinel*/<!Const> s)
      requires Const && convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    template<bool OtherConst>
      requires sentinel_for<sentinel_t</*Base*/>,
                            iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);
  };
}

类模板 std::ranges::join_with_view

namespace std::ranges {
  template<class R>
  concept /*bidirectional-common*/ =
    bidirectional_range<R> && common_range<R>; // 仅用于阐述

  template<input_range V, forward_range Pattern>
    requires view<V> && input_range<range_reference_t<V>> && view<Pattern> &&
             /*concatable*/<range_reference_t<V>, Pattern>
  class join_with_view : public view_interface<join_with_view<V, Pattern>>
  {
    using /*InnerRng*/ = range_reference_t<V>; // 仅用于阐述

    V /*base_*/        = V();                               // 仅用于阐述
    /*non-propagating-cache*/<iterator_t<V>> /*outer-it_*/; // 仅用于阐述；仅当 !forward_range<V> 时存在
    /*non-propagating-cache*/<remove_cv_t</*InnerRng*/>>
      /*inner_*/;                     // 仅用于阐述；仅当 is_reference_v<InnerRng> 为 false 时存在
    Pattern /*pattern_*/ = Pattern(); // 仅用于阐述

    // 类模板 join_with_view::iterator
    template<bool Const>
    struct /*iterator*/; // 仅用于阐述

    // 类模板 join_with_view::sentinel
    template<bool Const>
    struct /*sentinel*/; // 仅用于阐述

  public:
    join_with_view()
      requires default_initializable<V> && default_initializable<Pattern>
    = default;

    constexpr explicit join_with_view(V base, Pattern pattern);

    template<input_range R>
      requires constructible_from<V, views::all_t<R>> &&
               constructible_from<Pattern, single_view<range_value_t</*InnerRng*/>>>
    constexpr explicit join_with_view(R&& r, range_value_t</*InnerRng*/> e);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
    {
      if constexpr (forward_range<V>) {
        constexpr bool use_const =
          /*simple-view*/<V> && is_reference_v</*InnerRng*/> && /*simple-view*/<Pattern>;
        return /*iterator*/<use_const>{ *this, ranges::begin(/*base_*/) };
      } else {
        /*outer-it_*/ = ranges::begin(/*base_*/);
        return /*iterator*/<false>{ *this };
      }
    }
    constexpr auto begin() const
      requires forward_range<const V> && forward_range<const Pattern> &&
               is_reference_v<range_reference_t<const V>> &&
               input_range<range_reference_t<const V>> &&
               /*concatable*/<range_reference_t<const V>, const Pattern>
    {
      return /*iterator*/<true>{ *this, ranges::begin(/*base_*/) };
    }

    constexpr auto end()
    {
      if constexpr (forward_range<V> && is_reference_v</*InnerRng*/> &&
                    forward_range</*InnerRng*/> && common_range<V> &&
                    common_range</*InnerRng*/>)
        return /*iterator*/ < /*simple-view*/<V> &&
               /*simple-view*/ < Pattern >> { *this, ranges::end(/*base_*/) };
      else
        return /*sentinel*/ < /*simple-view*/<V> &&
               /*simple-view*/ < Pattern >> { *this };
    }
    constexpr auto end() const
      requires forward_range<const V> && forward_range<const Pattern> &&
               is_reference_v<range_reference_t<const V>> &&
               input_range<range_reference_t<const V>> &&
               /*concatable*/<range_reference_t<const V>, const Pattern>
    {
      using InnerConstRng = range_reference_t<const V>;
      if constexpr (forward_range<InnerConstRng> && common_range<const V> &&
                    common_range<InnerConstRng>)
        return /*iterator*/<true>{ *this, ranges::end(/*base_*/) };
      else
        return /*sentinel*/<true>{ *this };
    }
  };

  template<class R, class P>
  join_with_view(R&&, P&&) -> join_with_view<views::all_t<R>, views::all_t<P>>;

  template<input_range R>
  join_with_view(R&&, range_value_t<range_reference_t<R>>)
    -> join_with_view<views::all_t<R>, single_view<range_value_t<range_reference_t<R>>>>;
}

类模板 std::ranges::join_with_view::iterator

namespace std::ranges {
  template<input_range V, forward_range Pattern>
    requires view<V> && input_range<range_reference_t<V>> && view<Pattern> &&
             /*concatable*/<range_reference_t<V>, Pattern>
  template<bool Const>
  class join_with_view<V, Pattern>::/*iterator*/
  {
    using /*Parent*/      = /*maybe-const*/<Const, join_with_view>; // 仅用于阐述
    using /*Base*/        = /*maybe-const*/<Const, V>;              // 仅用于阐述
    using /*InnerBase*/   = range_reference_t</*Base*/>;            // 仅用于阐述
    using /*PatternBase*/ = /*maybe-const*/<Const, Pattern>;        // 仅用于阐述

    using /*OuterIter*/   = iterator_t</*Base*/>;        // 仅用于阐述
    using /*InnerIter*/   = iterator_t</*InnerBase*/>;   // 仅用于阐述
    using /*PatternIter*/ = iterator_t</*PatternBase*/>; // 仅用于阐述

    static constexpr bool /*ref-is-glvalue*/ =
      is_reference_v</*InnerBase*/>; // 仅用于阐述

    /*Parent*/* /*parent_*/     = nullptr;                 // 仅用于阐述
    /*OuterIter*/ /*outer-it_*/ = /*OuterIter*/();         // 仅用于阐述；仅当 Base 实现 forward_range 时存在
    variant</*PatternIter*/, /*InnerIter*/> /*inner-it_*/; // 仅用于阐述

    constexpr /*iterator*/(/*Parent*/& parent, /*OuterIter*/ outer)
      requires forward_range</*Base*/>; // 仅用于阐述
    constexpr explicit /*iterator*/(/*Parent*/& parent)
      requires(!forward_range</*Base*/>);             // 仅用于阐述
    constexpr /*OuterIter*/& /*outer*/();             // 仅用于阐述
    constexpr const /*OuterIter*/& /*outer*/() const; // 仅用于阐述
    constexpr auto& /*update-inner*/();               // 仅用于阐述
    constexpr auto& /*get-inner*/();                  // 仅用于阐述
    constexpr void /*satisfy*/();                     // 仅用于阐述

  public:
    using iterator_concept  = /* 见描述 */;
    using iterator_category = /* 见描述 */; // 不总存在
    using value_type        = /* 见描述 */;
    using difference_type   = /* 见描述 */;

    /*iterator*/()          = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, /*OuterIter*/> &&
               convertible_to<iterator_t</*InnerRng*/>, /*InnerIter*/> &&
               convertible_to<iterator_t<Pattern>, /*PatternIter*/>;

    constexpr decltype(auto) operator*() const;

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires /*ref-is-glvalue*/
               && forward_iterator</*OuterIter*/> && forward_iterator</*InnerIter*/>;

    constexpr /*iterator*/& operator--()
      requires /*ref-is-glvalue*/ && bidirectional_range</*Base*/> &&
               /*bidirectional-common*/</*InnerBase*/> &&
               /*bidirectional-common*/</*PatternBase*/>;
    constexpr /*iterator*/ operator--(int)
      requires /*ref-is-glvalue*/ && bidirectional_range</*Base*/> &&
               /*bidirectional-common*/</*InnerBase*/> &&
               /*bidirectional-common*/</*PatternBase*/>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires /*ref-is-glvalue*/
               && forward_range</*Base*/> && equality_comparable</*InnerIter*/>;

    friend constexpr decltype(auto) iter_move(const /*iterator*/& x)
    {
      using rvalue_reference =
        common_reference_t<iter_rvalue_reference_t</*InnerIter*/>,
                           iter_rvalue_reference_t</*PatternIter*/>>;
      return visit<rvalue_reference>(ranges::iter_move, x./*inner-it_*/);
    }

    friend constexpr void iter_swap(const /*iterator*/& x, const /*iterator*/& y)
      requires indirectly_swappable</*InnerIter*/, /*PatternIter*/>
    {
      visit(ranges::iter_swap, x./*inner-it_*/, y./*inner-it_*/);
    }
  };
}

类模板 std::ranges::join_with_view::sentinel

namespace std::ranges {
  template<input_range V, forward_range Pattern>
    requires view<V> && input_range<range_reference_t<V>> && view<Pattern> &&
             /*concatable*/<range_reference_t<V>, Pattern>
  template<bool Const>
  class join_with_view<V, Pattern>::/*sentinel*/
  {
    using /*Parent*/ = /*maybe-const*/<Const, join_with_view>; // 仅用于阐述
    using /*Base*/   = /*maybe-const*/<Const, V>;              // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/ = sentinel_t</*Base*/>();    // 仅用于阐述

    constexpr explicit /*sentinel*/(/*Parent*/& parent); // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr /*sentinel*/(/*sentinel*/<!Const> s)
      requires Const && convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    template<bool OtherConst>
      requires sentinel_for<sentinel_t</*Base*/>,
                            iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);
  };
}

类模板 std::ranges::lazy_split_view

namespace std::ranges {
  template<auto>
  struct /*require-constant*/; // 仅用于阐述

  template<class R>
  concept /*tiny-range*/ = // 仅用于阐述
    sized_range<R> && requires {
      typename /*require-constant*/<remove_reference_t<R>::size()>;
    } && (remove_reference_t<R>::size() <= 1);

  template<input_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>,
                                   iterator_t<Pattern>,
                                   ranges::equal_to> &&
             (forward_range<V> || /*tiny-range*/<Pattern>)
  class lazy_split_view : public view_interface<lazy_split_view<V, Pattern>>
  {
  private:
    V /*base_*/          = V();       // 仅用于阐述
    Pattern /*pattern_*/ = Pattern(); // 仅用于阐述

    /*non-propagating-cache*/<iterator_t<V>> /*current_*/; // 仅用于阐述；仅当 forward_range<V> 为 false 时存在

    // 类模板 lazy_split_view::outer-iterator
    template<bool>
    struct /*outer-iterator*/; // 仅用于阐述

    // 类模板 lazy_split_view::inner-iterator
    template<bool>
    struct /*inner-iterator*/; // 仅用于阐述

  public:
    lazy_split_view()
      requires default_initializable<V> && default_initializable<Pattern>
    = default;
    constexpr explicit lazy_split_view(V base, Pattern pattern);

    template<input_range R>
      requires constructible_from<V, views::all_t<R>> &&
               constructible_from<Pattern, single_view<range_value_t<R>>>
    constexpr explicit lazy_split_view(R&& r, range_value_t<R> e);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
    {
      if constexpr (forward_range<V>) {
        return /*outer-iterator*/ < /*simple-view*/<V> &&
               /*simple-view*/ < Pattern >> { *this, ranges::begin(/*base_*/) };
      } else {
        /*current_*/ = ranges::begin(/*base_*/);
        return /*outer-iterator*/<false>{ *this };
      }
    }

    constexpr auto begin() const
      requires forward_range<V> && forward_range<const V>
    {
      return /*outer-iterator*/<true>{ *this, ranges::begin(/*base_*/) };
    }

    constexpr auto end()
      requires forward_range<V> && common_range<V>
    {
      return /*outer-iterator*/ < /*simple-view*/<V> &&
             /*simple-view*/ < Pattern >> { *this, ranges::end(/*base_*/) };
    }

    constexpr auto end() const
    {
      if constexpr (forward_range<V> && forward_range<const V> && common_range<const V>)
        return /*outer-iterator*/<true>{ *this, ranges::end(/*base_*/) };
      else
        return default_sentinel;
    }
  };

  template<class R, class P>
  lazy_split_view(R&&, P&&) -> lazy_split_view<views::all_t<R>, views::all_t<P>>;

  template<input_range R>
  lazy_split_view(R&&, range_value_t<R>)
    -> lazy_split_view<views::all_t<R>, single_view<range_value_t<R>>>;
}

类模板 std::ranges::lazy_split_view::outer_iterator

namespace std::ranges {
  template<input_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>,
                                   iterator_t<Pattern>,
                                   ranges::equal_to> &&
             (forward_range<V> || /*tiny-range*/<Pattern>)
  template<bool Const>
  struct lazy_split_view<V, Pattern>::/*outer-iterator*/
  {
  private:
    using /*Parent*/        = /*maybe-const*/<Const, lazy_split_view>; // 仅用于阐述
    using /*Base*/          = /*maybe-const*/<Const, V>;               // 仅用于阐述
    /*Parent*/* /*parent_*/ = nullptr;                                 // 仅用于阐述

    iterator_t</*Base*/> /*current_*/ =
      iterator_t</*Base*/>(); // 仅用于阐述；仅当 V 实现 forward_range 时存在

    bool /*trailing-empty_*/ = false; // 仅用于阐述

  public:
    using iterator_concept =
      conditional_t<forward_range</*Base*/>, forward_iterator_tag, input_iterator_tag>;

    using iterator_category = input_iterator_tag; // 仅当 Base 实现 forward_range 时存在

    // 类 lazy_split_view::outer-iterator::value_type
    struct value_type;
    using difference_type = range_difference_t</*Base*/>;

    /*outer-iterator*/()  = default;
    constexpr explicit /*outer-iterator*/(/*Parent*/& parent)
      requires(!forward_range</*Base*/>);
    constexpr /*outer-iterator*/(/*Parent*/& parent, iterator_t</*Base*/> current)
      requires forward_range</*Base*/>;
    constexpr /*outer-iterator*/(/*outer-iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>>;

    constexpr value_type operator*() const;

    constexpr /*outer-iterator*/& operator++();
    constexpr decltype(auto) operator++(int)
    {
      if constexpr (forward_range</*Base*/>) {
        auto tmp = *this;
        ++*this;
        return tmp;
      } else
        ++*this;
    }

    friend constexpr bool operator==(const /*outer-iterator*/& x,
                                     const /*outer-iterator*/& y)
      requires forward_range</*Base*/>;

    friend constexpr bool operator==(const /*outer-iterator*/& x, default_sentinel_t);
  };
}

类模板 std::ranges::lazy_split_view::outer_iterator::value_type

namespace std::ranges {
  template<input_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>,
                                   iterator_t<Pattern>,
                                   ranges::equal_to> &&
             (forward_range<V> || /*tiny-range*/<Pattern>)
  template<bool Const>
  struct lazy_split_view<V, Pattern>::/*outer-iterator*/<Const>::value_type
    : view_interface<value_type>
  {
  private:
    /*outer-iterator*/ /*i_*/ = /*outer-iterator*/(); // 仅用于阐述

    constexpr explicit value_type(/*outer-iterator*/ i); // 仅用于阐述

  public:
    constexpr /*inner-iterator*/<Const> begin() const;
    constexpr default_sentinel_t end() const noexcept;
  };
}

类模板 std::ranges::lazy_split_view::inner_iterator

namespace std::ranges {
  template<input_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>,
                                   iterator_t<Pattern>,
                                   ranges::equal_to> &&
             (forward_range<V> || /*tiny-range*/<Pattern>)
  template<bool Const>
  struct lazy_split_view<V, Pattern>::/*inner-iterator*/
  {
  private:
    using /*Base*/                   = /*maybe-const*/<Const, V>;   // 仅用于阐述
    /*outer-iterator*/<Const> /*i_*/ = /*outer-iterator*/<Const>(); // 仅用于阐述
    bool /*incremented_*/            = false;                       // 仅用于阐述

  public:
    using iterator_concept  = typename /*outer-iterator*/<Const>::iterator_concept;

    using iterator_category = /* 见描述 */; // 仅当 Base 实现 forward_range 时存在
    using value_type      = range_value_t</*Base*/>;
    using difference_type = range_difference_t</*Base*/>;

    /*inner-iterator*/()  = default;
    constexpr explicit /*inner-iterator*/(/*outer-iterator*/<Const> i);

    constexpr const iterator_t</*Base*/>& base() const& noexcept;
    constexpr iterator_t</*Base*/> base() &&
        requires forward_range<V>;

    constexpr decltype(auto) operator*() const { return */*i_*/./*current*/; }

    constexpr /*inner-iterator*/& operator++();
    constexpr decltype(auto) operator++(int)
    {
      if constexpr (forward_range</*Base*/>) {
        auto tmp = *this;
        ++*this;
        return tmp;
      } else
        ++*this;
    }

    friend constexpr bool operator==(const /*inner-iterator*/& x,
                                     const /*inner-iterator*/& y)
      requires forward_range</*Base*/>;

    friend constexpr bool operator==(const /*inner-iterator*/& x, default_sentinel_t);

    friend constexpr decltype(auto) iter_move(const /*inner-iterator*/& i) noexcept(
      noexcept(ranges::iter_move(i./*i_*/./*current*/)))
    {
      return ranges::iter_move(i./*i_*/./*current*/);
    }

    friend constexpr void
    iter_swap(const /*inner-iterator*/& x, const /*inner-iterator*/& y) noexcept(
      noexcept(ranges::iter_swap(x./*i_*/./*current*/, y./*i_*/./*current*/)))
      requires indirectly_swappable<iterator_t</*Base*/>>;
  };
}

类模板 std::ranges::split_view

namespace std::ranges {
  template<forward_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to>
  class split_view : public view_interface<split_view<V, Pattern>>
  {
  private:
    V /*base_*/          = V();       // 仅用于阐述
    Pattern /*pattern_*/ = Pattern(); // 仅用于阐述

    // 类 split_view::iterator
    struct /*iterator*/; // 仅用于阐述

    // 类 split_view::sentinel
    struct /*sentinel*/; // 仅用于阐述

  public:
    split_view()
      requires default_initializable<V> && default_initializable<Pattern>
    = default;
    constexpr explicit split_view(V base, Pattern pattern);

    template<forward_range R>
      requires constructible_from<V, views::all_t<R>> &&
               constructible_from<Pattern, single_view<range_value_t<R>>>
    constexpr explicit split_view(R&& r, range_value_t<R> e);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr /*iterator*/ begin();

    constexpr auto end()
    {
      if constexpr (common_range<V>) {
        return /*iterator*/{ *this, ranges::end(/*base_*/), {} };
      } else {
        return /*sentinel*/{ *this };
      }
    }

    constexpr subrange<iterator_t<V>> /*find-next*/(iterator_t<V>); // 仅用于阐述
  };

  template<class R, class P>
  split_view(R&&, P&&) -> split_view<views::all_t<R>, views::all_t<P>>;

  template<forward_range R>
  split_view(R&&, range_value_t<R>)
    -> split_view<views::all_t<R>, single_view<range_value_t<R>>>;
}

类模板 std::ranges::split_view::iterator

namespace std::ranges {
  template<forward_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to>
  class split_view<V, Pattern>::/*iterator*/
  {
  private:
    split_view* /*parent_*/           = nullptr;                   // 仅用于阐述
    iterator_t<V> /*cur_*/            = iterator_t<V>();           // 仅用于阐述
    subrange<iterator_t<V>> /*next_*/ = subrange<iterator_t<V>>(); // 仅用于阐述
    bool /*trailing-empty_*/          = false;                     // 仅用于阐述

  public:
    using iterator_concept  = forward_iterator_tag;
    using iterator_category = input_iterator_tag;
    using value_type        = subrange<iterator_t<V>>;
    using difference_type   = range_difference_t<V>;

    /*iterator*/()          = default;
    constexpr /*iterator*/(split_view& parent,
                           iterator_t<V> current,
                           subrange<iterator_t<V>> next);

    constexpr iterator_t<V> base() const;
    constexpr value_type operator*() const;

    constexpr /*iterator*/& operator++();
    constexpr /*iterator*/ operator++(int);

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y);
  };
}

类模板 std::ranges::split_view::sentinel

namespace std::ranges {
  template<forward_range V, forward_range Pattern>
    requires view<V> && view<Pattern> &&
             indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to>
  struct split_view<V, Pattern>::/*sentinel*/
  {
  private:
    sentinel_t<V> /*end_*/ = sentinel_t<V>(); // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr explicit /*sentinel*/(split_view& parent);

    friend constexpr bool operator==(const /*iterator*/& x, const /*sentinel*/& y);
  };
}

类模板 std::ranges::concat

namespace std::ranges {
  template<class... Rs>
  using /*concat-reference-t*/ =
    common_reference_t<range_reference_t<Rs>...>; // 仅用于阐述
  template<class... Rs>
  using /*concat-value-t*/ = common_type_t<range_value_t<Rs>...>; // 仅用于阐述
  template<class... Rs>
  using /*concat-rvalue-reference-t*/ = // 仅用于阐述
    common_reference_t<range_rvalue_reference_t<Rs>...>;

  template<class... Rs>
  concept /*concat-indirectly-readable*/ = /* 见描述 */; // 仅用于阐述
  template<class... Rs>
  concept /*concatable*/ = /* 见描述 */; // 仅用于阐述
  template<bool Const, class... Rs>
  concept /*concat-is-random-access*/ = /* 见描述 */; // 仅用于阐述
  template<bool Const, class... Rs>
  concept /*concat-is-bidirectional*/ = /* 见描述 */; // 仅用于阐述

  template<input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0) && /*concatable*/<Views...>
  class concat_view : public view_interface<concat_view<Views...>>
  {
    tuple<Views...> /*views_*/; // 仅用于阐述

    // 类模板 concat_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述

  public:
    constexpr concat_view() = default;
    constexpr explicit concat_view(Views... views);

    constexpr /*iterator*/<false> begin()
      requires(!(/*simple-view*/<Views> && ...));
    constexpr /*iterator*/<true> begin() const
      requires(range<const Views> && ...) && /*concatable*/<const Views...>;

    constexpr auto end()
      requires(!(/*simple-view*/<Views> && ...));
    constexpr auto end() const
      requires(range<const Views> && ...) && /*concatable*/<const Views...>;

    constexpr auto size()
      requires(sized_range<Views> && ...);
    constexpr auto size() const
      requires(sized_range<const Views> && ...);
  };

  template<class... R>
  concat_view(R&&...) -> concat_view<views::all_t<R>...>;
}

类模板 std::ranges::concat::iterator

namespace std::ranges {
  template<input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0) && /*concatable*/<Views...>
  template<bool Const>
  class concat_view<Views...>::/*iterator*/
  {
  public:
    using iterator_category = /* 见描述 */; // 不总存在
    using iterator_concept  = /* 见描述 */;
    using value_type        = /*concat-value-t*/</*maybe-const*/<Const, Views>...>;
    using difference_type =
      common_type_t<range_difference_t</*maybe-const*/<Const, Views>>...>;

  private:
    using /*base-iter*/ = // 仅用于阐述
      variant<iterator_t</*maybe-const*/<Const, Views>>...>;

    /*maybe-const*/<Const, concat_view>* /*parent_*/ = nullptr; // 仅用于阐述
    /*base-iter*/ /*it_*/;                                      // 仅用于阐述

    template<size_t N>
    constexpr void /*satisfy*/(); // 仅用于阐述
    template<size_t N>
    constexpr void /*prev*/(); // 仅用于阐述

    template<size_t N>
    constexpr void /*advance-fwd*/(difference_type offset, // 仅用于阐述
                                   difference_type steps);
    template<size_t N>
    constexpr void /*advance-bwd*/(difference_type offset, // 仅用于阐述
                                   difference_type steps);

    template<class... Args>
    constexpr explicit /*iterator*/(
      /*maybe-const*/<Const, concat_view>* parent, // 仅用于阐述
      Args&&... args)
      requires constructible_from</*base-iter*/, Args&&...>;

  public:
    /*iterator*/() = default;

    constexpr /*iterator*/(iterator<!Const> i)
      requires Const &&
               (convertible_to<iterator_t<Views>, iterator_t<const Views>> && ...);

    constexpr decltype(auto) operator*() const;
    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires /*all-forward*/<Const, Views...>;
    constexpr /*iterator*/& operator--()
      requires /*concat-is-bidirectional*/<Const, Views...>;
    constexpr /*iterator*/ operator--(int)
      requires /*concat-is-bidirectional*/<Const, Views...>;
    constexpr /*iterator*/& operator+=(difference_type n)
      requires /*concat-is-random-access*/<Const, Views...>;
    constexpr /*iterator*/& operator-=(difference_type n)
      requires /*concat-is-random-access*/<Const, Views...>;
    constexpr decltype(auto) operator[](difference_type n) const
      requires /*concat-is-random-access*/<Const, Views...>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires(equality_comparable<iterator_t</*maybe-const*/<Const, Views>>> && ...);
    friend constexpr bool operator==(const /*iterator*/& it, default_sentinel_t);
    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires /*all-random-access*/<Const, Views...>;
    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires /*all-random-access*/<Const, Views...>;
    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires /*all-random-access*/<Const, Views...>;
    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires /*all-random-access*/<Const, Views...>;
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires(/*all-random-access*/<Const, Views...> &&
               (three_way_comparable<iterator_t</*maybe-const*/<Const, Views>>> && ...));
    friend constexpr /*iterator*/ operator+(const /*iterator*/& it, difference_type n)
      requires /*concat-is-random-access*/<Const, Views...>;
    friend constexpr /*iterator*/ operator+(difference_type n, const /*iterator*/& it)
      requires /*concat-is-random-access*/<Const, Views...>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& it, difference_type n)
      requires /*concat-is-random-access*/<Const, Views...>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires /*concat-is-random-access*/<Const, Views...>;
    friend constexpr difference_type operator-(const /*iterator*/& x, default_sentinel_t)
      requires /* 见描述 */;
    friend constexpr difference_type operator-(default_sentinel_t, const /*iterator*/& x)
      requires /* 见描述 */;
    friend constexpr decltype(auto) iter_move(const /*iterator*/& it) noexcept(
      /* 见描述 */);
    friend constexpr void iter_swap(const /*iterator*/& x,
                                    const /*iterator*/& y) noexcept(/* 见描述 */)
      requires /* 见描述 */;
  };
}

类模板 std::ranges::common_view

namespace std::ranges {
  template<view V>
    requires(!common_range<V> && copyable<iterator_t<V>>)
  class common_view : public view_interface<common_view<V>>
  {
  private:
    V /*base_*/ = V(); // 仅用于阐述

  public:
    common_view()
      requires default_initializable<V>
    = default;

    constexpr explicit common_view(V r);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (random_access_range<V> && sized_range<V>)
        return ranges::begin(/*base_*/);
      else
        return common_iterator<iterator_t<V>, sentinel_t<V>>(ranges::begin(/*base_*/));
    }

    constexpr auto begin() const
      requires range<const V>
    {
      if constexpr (random_access_range<const V> && sized_range<const V>)
        return ranges::begin(/*base_*/);
      else
        return common_iterator<iterator_t<const V>, sentinel_t<const V>>(
          ranges::begin(/*base_*/));
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (random_access_range<V> && sized_range<V>)
        return ranges::begin(/*base_*/) + ranges::distance(/*base_*/);
      else
        return common_iterator<iterator_t<V>, sentinel_t<V>>(ranges::end(/*base_*/));
    }

    constexpr auto end() const
      requires range<const V>
    {
      if constexpr (random_access_range<const V> && sized_range<const V>)
        return ranges::begin(/*base_*/) + ranges::distance(/*base_*/);
      else
        return common_iterator<iterator_t<const V>, sentinel_t<const V>>(
          ranges::end(/*base_*/));
    }

    constexpr auto size()
      requires sized_range<V>
    {
      return ranges::size(/*base_*/);
    }
    constexpr auto size() const
      requires sized_range<const V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
  };

  template<class R>
  common_view(R&&) -> common_view<views::all_t<R>>;
}

类模板 std::ranges::reverse_view

namespace std::ranges {
  template<view V>
    requires bidirectional_range<V>
  class reverse_view : public view_interface<reverse_view<V>>
  {
  private:
    V /*base_*/ = V(); // 仅用于阐述

  public:
    reverse_view()
      requires default_initializable<V>
    = default;

    constexpr explicit reverse_view(V r);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr reverse_iterator<iterator_t<V>> begin();
    constexpr reverse_iterator<iterator_t<V>> begin()
      requires common_range<V>;
    constexpr auto begin() const
      requires common_range<const V>;

    constexpr reverse_iterator<iterator_t<V>> end();
    constexpr auto end() const
      requires common_range<const V>;

    constexpr auto size()
      requires sized_range<V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto size() const
      requires sized_range<const V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
  };

  template<class R>
  reverse_view(R&&) -> reverse_view<views::all_t<R>>;
}

类模板 std::ranges::as_const_view

namespace std::ranges {
  template<view V>
    requires input_range<V>
  class as_const_view : public view_interface<as_const_view<V>>
  {
    V /*base_*/ = V(); // 仅用于阐述

  public:
    as_const_view()
      requires default_initializable<V>
    = default;
    constexpr explicit as_const_view(V base);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      return ranges::cbegin(/*base_*/);
    }
    constexpr auto begin() const
      requires range<const V>
    {
      return ranges::cbegin(/*base_*/);
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      return ranges::cend(/*base_*/);
    }
    constexpr auto end() const
      requires range<const V>
    {
      return ranges::cend(/*base_*/);
    }

    constexpr auto size()
      requires sized_range<V>
    {
      return ranges::size(/*base_*/);
    }
    constexpr auto size() const
      requires sized_range<const V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
  };

  template<class R>
  as_const_view(R&&) -> as_const_view<views::all_t<R>>;
}

类模板 std::ranges::elements_view

namespace std::ranges {
  template<class T, size_t N>
  concept /*has-tuple-element*/ = // 仅用于阐述
    /*tuple-like*/<T> && N < tuple_size_v<T>;

  template<class T, size_t N>
  concept /*returnable-element*/ = // 仅用于阐述
    is_reference_v<T> || move_constructible<tuple_element_t<N, T>>;

  template<input_range V, size_t N>
    requires view<V> && /*has-tuple-element*/<range_value_t<V>, N> &&
             /*has-tuple-element*/<remove_reference_t<range_reference_t<V>>, N> &&
             /*returnable-element*/<range_reference_t<V>, N>
  class elements_view : public view_interface<elements_view<V, N>>
  {
  public:
    elements_view()
      requires default_initializable<V>
    = default;
    constexpr explicit elements_view(V base);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      return /*iterator*/<false>(ranges::begin(/*base_*/));
    }

    constexpr auto begin() const
      requires range<const V>
    {
      return /*iterator*/<true>(ranges::begin(/*base_*/));
    }

    constexpr auto end()
      requires(!/*simple-view*/<V> && !common_range<V>)
    {
      return /*sentinel*/<false>{ ranges::end(/*base_*/) };
    }

    constexpr auto end()
      requires(!/*simple-view*/<V> && common_range<V>)
    {
      return /*iterator*/<false>{ ranges::end(/*base_*/) };
    }

    constexpr auto end() const
      requires range<const V>
    {
      return /*sentinel*/<true>{ ranges::end(/*base_*/) };
    }

    constexpr auto end() const
      requires common_range<const V>
    {
      return /*iterator*/<true>{ ranges::end(/*base_*/) };
    }

    constexpr auto size()
      requires sized_range<V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto size() const
      requires sized_range<const V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>
    {
      return ranges::reserve_hint(/*base_*/);
    }

    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>
    {
      return ranges::reserve_hint(/*base_*/);
    }

  private:
    // 类模板 elements_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述

    // 类模板 elements_view::sentinel
    template<bool>
    class /*sentinel*/; // 仅用于阐述

    V /*base_*/ = V(); // 仅用于阐述
  };
}

类模板 std::ranges::elements_view::iterator

namespace std::ranges {
  template<input_range V, size_t N>
    requires view<V> && /*has-tuple-element*/<range_value_t<V>, N> &&
             /*has-tuple-element*/<remove_reference_t<range_reference_t<V>>, N> &&
             /*returnable-element*/<range_reference_t<V>, N>
  template<bool Const>
  class elements_view<V, N>::/*iterator*/
  {
    using /*Base*/                    = /*maybe-const*/<Const, V>; // 仅用于阐述

    iterator_t</*Base*/> /*current_*/ = iterator_t</*Base*/>(); // 仅用于阐述

    static constexpr decltype(auto) /*get-element*/(
      const iterator_t</*Base*/>& i); // 仅用于阐述

  public:
    using iterator_concept  = /* 见描述 */;
    using iterator_category = /* 见描述 */; // 不总存在
    using value_type        = remove_cvref_t<tuple_element_t<N, range_value_t</*Base*/>>>;
    using difference_type   = range_difference_t</*Base*/>;

    /*iterator*/()
      requires default_initializable<iterator_t</*Base*/>>
    = default;
    constexpr explicit /*iterator*/(iterator_t</*Base*/> current);
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>>;

    constexpr const iterator_t</*Base*/>& base() const& noexcept;
    constexpr iterator_t</*Base*/> base() &&;

    constexpr decltype(auto) operator*() const { return /*get-element*/(/*current_*/); }

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires forward_range</*Base*/>;

    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;

    constexpr /*iterator*/& operator+=(difference_type x)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires random_access_range</*Base*/>;

    constexpr decltype(auto) operator[](difference_type n) const
      requires random_access_range</*Base*/>
    {
      return /*get-element*/(/*current_*/ + n);
    }

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires equality_comparable<iterator_t</*Base*/>>;

    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/> && three_way_comparable<iterator_t</*Base*/>>
    ;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& x, difference_type y)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& x, difference_type y)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires sized_sentinel_for<iterator_t</*Base*/>, iterator_t</*Base*/>>;
  };
}

类模板 std::ranges::elements_view::sentinel

namespace std::ranges {
  template<input_range V, size_t N>
    requires view<V> && /*has-tuple-element*/<range_value_t<V>, N> &&
             /*has-tuple-element*/<remove_reference_t<range_reference_t<V>>, N> &&
             /*returnable-element*/<range_reference_t<V>, N>
  template<bool Const>
  class elements_view<V, N>::/*sentinel*/
  {
  private:
    using /*Base*/                = /*maybe-const*/<Const, V>; // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/ = sentinel_t</*Base*/>();    // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr explicit /*sentinel*/(sentinel_t</*Base*/> end);
    constexpr /*sentinel*/(/*sentinel*/<!Const> other)
      requires Const && convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    constexpr sentinel_t</*Base*/> base() const;

    template<bool OtherConst>
      requires sentinel_for<sentinel_t</*Base*/>,
                            iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for<sentinel_t</*Base*/>,
                                  iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, V>> operator-(
      const /*iterator*/<OtherConst>& x,
      const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for<sentinel_t</*Base*/>,
                                  iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, V>> operator-(
      const /*sentinel*/& x,
      const /*iterator*/<OtherConst>& y);
  };
}

类模板 std::ranges::enumerate_view

namespace std::ranges {
  template<view V>
    requires /*range-with-movable-references*/<V>
  class enumerate_view : public view_interface<enumerate_view<V>>
  {
    V /*base_*/ = V(); // 仅用于阐述

    // 类模板 enumerate_view::iterator
    template<bool Const>
    class /*iterator*/; // 仅用于阐述

    // 类模板 enumerate_view::sentinel
    template<bool Const>
    class /*sentinel*/; // 仅用于阐述

  public:
    constexpr enumerate_view()
      requires default_initializable<V>
    = default;
    constexpr explicit enumerate_view(V base);

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      return /*iterator*/<false>(ranges::begin(/*base_*/), 0);
    }
    constexpr auto begin() const
      requires /*range-with-movable-references*/<const V>
    {
      return /*iterator*/<true>(ranges::begin(/*base_*/), 0);
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (forward_range<V> && common_range<V> && sized_range<V>)
        return /*iterator*/<false>(ranges::end(/*base_*/), ranges::distance(/*base_*/));
      else
        return /*sentinel*/<false>(ranges::end(/*base_*/));
    }
    constexpr auto end() const
      requires /*range-with-movable-references*/<const V>
    {
      if constexpr (forward_range<const V> && common_range<const V> &&
                    sized_range<const V>)
        return /*iterator*/<true>(ranges::end(/*base_*/), ranges::distance(/*base_*/));
      else
        return /*sentinel*/<true>(ranges::end(/*base_*/));
    }

    constexpr auto size()
      requires sized_range<V>
    {
      return ranges::size(/*base_*/);
    }
    constexpr auto size() const
      requires sized_range<const V>
    {
      return ranges::size(/*base_*/);
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>
    {
      return ranges::reserve_hint(/*base_*/);
    }
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>
    {
      return ranges::reserve_hint(/*base_*/);
    }

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }
  };

  template<class R>
  enumerate_view(R&&) -> enumerate_view<views::all_t<R>>;
}

类模板 std::ranges::enumerate_view::iterator

namespace std::ranges {
  template<view V>
    requires /*range-with-movable-references*/<V>
  template<bool Const>
  class enumerate_view<V>::/*iterator*/
  {
    using /*Base*/ = /*maybe-const*/<Const, V>; // 仅用于阐述

  public:
    using iterator_category = input_iterator_tag;
    using iterator_concept  = /* 见描述 */;
    using difference_type   = range_difference_t</*Base*/>;
    using value_type        = tuple<difference_type, range_value_t</*Base*/>>;

  private:
    using /*reference-type*/ = // 仅用于阐述
      tuple<difference_type, range_reference_t</*Base*/>>;
    iterator_t</*Base*/> /*current_*/ = iterator_t</*Base*/>(); // 仅用于阐述
    difference_type /*pos_*/          = 0;                      // 仅用于阐述

    constexpr explicit /*iterator*/(iterator_t</*Base*/> current,
                                    difference_type pos); // 仅用于阐述

  public:
    /*iterator*/()
      requires default_initializable<iterator_t</*Base*/>>
    = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>>;

    constexpr const iterator_t</*Base*/>& base() const& noexcept;
    constexpr iterator_t</*Base*/> base() &&;

    constexpr difference_type index() const noexcept;

    constexpr auto operator*() const
    {
      return /*reference-type*/(/*pos_*/, */*current_*/);
    }

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires forward_range</*Base*/>;

    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;

    constexpr /*iterator*/& operator+=(difference_type x)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires random_access_range</*Base*/>;

    constexpr auto operator[](difference_type n) const
      requires random_access_range</*Base*/>
    {
      return /*reference-type*/(/*pos_*/ + n, /*current_*/[n]);
    }

    friend constexpr bool operator==(const /*iterator*/& x,
                                     const /*iterator*/& y) noexcept;
    friend constexpr strong_ordering operator<=>(const /*iterator*/& x,
                                                 const /*iterator*/& y) noexcept;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& x, difference_type y)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& x, difference_type y)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y) noexcept;

    friend constexpr auto iter_move(const /*iterator*/& i) noexcept(
      noexcept(ranges::iter_move(i./*current_*/)) &&
      is_nothrow_move_constructible_v<range_rvalue_reference_t</*Base*/>>)
    {
      return tuple<difference_type, range_rvalue_reference_t</*Base*/>>(
        i./*pos_*/, ranges::iter_move(i./*current_*/));
    }
  };
}

类模板 std::ranges::enumerate_view::sentinel

namespace std::ranges {
  template<view V>
    requires /*range-with-movable-references*/<V>
  template<bool Const>
  class enumerate_view<V>::/*sentinel*/
  {
    using /*Base*/                = /*maybe-const*/<Const, V>; // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/ = sentinel_t</*Base*/>();    // 仅用于阐述
    constexpr explicit /*sentinel*/(sentinel_t</*Base*/> end); // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr /*sentinel*/(/*sentinel*/<!Const> other)
      requires Const && convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    constexpr sentinel_t</*Base*/> base() const;

    template<bool OtherConst>
      requires sentinel_for<sentinel_t</*Base*/>,
                            iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for<sentinel_t</*Base*/>,
                                  iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, V>> operator-(
      const /*iterator*/<OtherConst>& x,
      const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for<sentinel_t</*Base*/>,
                                  iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, V>> operator-(
      const /*sentinel*/& x,
      const /*iterator*/<OtherConst>& y);
  };
}

类模板 std::ranges::zip_view

namespace std::ranges {
  template<class... Rs>
  concept /*zip-is-common*/ = // 仅用于阐述
    (sizeof...(Rs) == 1 && (common_range<Rs> && ...)) ||
    (!(bidirectional_range<Rs> && ...) && (common_range<Rs> && ...)) ||
    ((random_access_range<Rs> && ...) && (sized_range<Rs> && ...));

  template<input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0)
  class zip_view : public view_interface<zip_view<Views...>>
  {
    tuple<Views...> /*views_*/; // 仅用于阐述

    // 类模板 zip_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述

    // 类模板 zip_view::sentinel
    template<bool>
    class /*sentinel*/; // 仅用于阐述

  public:
    zip_view() = default;
    constexpr explicit zip_view(Views... views);

    constexpr auto begin()
      requires(!(/*simple-view*/<Views> && ...))
    {
      return /*iterator*/<false>(/*tuple-transform*/(ranges::begin, /*views_*/));
    }
    constexpr auto begin() const
      requires(range<const Views> && ...)
    {
      return /*iterator*/<true>(/*tuple-transform*/(ranges::begin, /*views_*/));
    }

    constexpr auto end()
      requires(!(/*simple-view*/<Views> && ...))
    {
      if constexpr (!/*zip-is-common*/<Views...>) {
        return /*sentinel*/<false>(/*tuple-transform*/(ranges::end, /*views_*/));
      } else if constexpr ((random_access_range<Views> && ...)) {
        return begin() + iter_difference_t</*iterator*/<false>>(size());
      } else {
        return /*iterator*/<false>(/*tuple-transform*/(ranges::end, /*views_*/));
      }
    }

    constexpr auto end() const
      requires(range<const Views> && ...)
    {
      if constexpr (!/*zip-is-common*/<const Views...>) {
        return /*sentinel*/<true>(/*tuple-transform*/(ranges::end, /*views_*/));
      } else if constexpr ((random_access_range<const Views> && ...)) {
        return begin() + iter_difference_t</*iterator*/<true>>(size());
      } else {
        return /*iterator*/<true>(/*tuple-transform*/(ranges::end, /*views_*/));
      }
    }

    constexpr auto size()
      requires(sized_range<Views> && ...);
    constexpr auto size() const
      requires(sized_range<const Views> && ...);
  };

  template<class... Rs>
  zip_view(Rs&&...) -> zip_view<views::all_t<Rs>...>;
}

类模板 std::ranges::zip_view::iterator

namespace std::ranges {
  template<input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0)
  template<bool Const>
  class zip_view<Views...>::/*iterator*/
  {
    tuple<iterator_t</*maybe-const*/<Const, Views>>...> /*current_*/; // 仅用于阐述
    constexpr explicit /*iterator*/(tuple<iterator_t</*maybe-const*/<Const, Views>>...>);
    // 仅用于阐述
  public:
    using iterator_category = input_iterator_tag; // 不总存在
    using iterator_concept  = /* 见描述 */;
    using value_type        = tuple<range_value_t</*maybe-const*/<Const, Views>>...>;
    using difference_type =
      common_type_t<range_difference_t</*maybe-const*/<Const, Views>>...>;

    /*iterator*/() = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const &&
               (convertible_to<iterator_t<Views>, iterator_t<const Views>> && ...);

    constexpr auto operator*() const;
    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires /*all-forward*/<Const, Views...>;

    constexpr /*iterator*/& operator--()
      requires /*all-bidirectional*/<Const, Views...>;
    constexpr /*iterator*/ operator--(int)
      requires /*all-bidirectional*/<Const, Views...>;

    constexpr /*iterator*/& operator+=(difference_type x)
      requires /*all-random-access*/<Const, Views...>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires /*all-random-access*/<Const, Views...>;

    constexpr auto operator[](difference_type n) const
      requires /*all-random-access*/<Const, Views...>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires(equality_comparable<iterator_t</*maybe-const*/<Const, Views>>> && ...);

    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires /*all-random-access*/<Const, Views...>;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& i, difference_type n)
      requires /*all-random-access*/<Const, Views...>;
    friend constexpr /*iterator*/ operator+(difference_type n, const /*iterator*/& i)
      requires /*all-random-access*/<Const, Views...>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& i, difference_type n)
      requires /*all-random-access*/<Const, Views...>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires(sized_sentinel_for<iterator_t</*maybe-const*/<Const, Views>>,
                                  iterator_t</*maybe-const*/<Const, Views>>> &&
               ...);

    friend constexpr auto iter_move(const /*iterator*/& i) noexcept(
      /* 见描述 */);

    friend constexpr void iter_swap(const /*iterator*/& l,
                                    const /*iterator*/& r) noexcept(/* 见描述 */)
      requires(indirectly_swappable<iterator_t</*maybe-const*/<Const, Views>>> && ...);
  };
}

类模板 std::ranges::zip_view::sentinel

namespace std::ranges {
  template<input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0)
  template<bool Const>
  class zip_view<Views...>::/*sentinel*/
  {
    tuple<sentinel_t</*maybe-const*/<Const, Views>>...> /*end_*/; // 仅用于阐述
    constexpr explicit /*sentinel*/(
      tuple<sentinel_t</*maybe-const*/<Const, Views>>...> end);   // 仅用于阐述
  public:
    /*sentinel*/() = default;
    constexpr /*sentinel*/(/*sentinel*/<!Const> i)
      requires Const &&
               (convertible_to<sentinel_t<Views>, sentinel_t<const Views>> && ...);

    template<bool OtherConst>
      requires(sentinel_for<sentinel_t</*maybe-const*/<Const, Views>>,
                            iterator_t</*maybe-const*/<OtherConst, Views>>> &&
               ...)
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);

    template<bool OtherConst>
      requires(sized_sentinel_for<sentinel_t</*maybe-const*/<Const, Views>>,
                                  iterator_t</*maybe-const*/<OtherConst, Views>>> &&
               ...)
    friend constexpr common_type_t<
      range_difference_t</*maybe-const*/<OtherConst, Views>>...>
    operator-(const /*iterator*/<OtherConst>& x, const /*sentinel*/& y);

    template<bool OtherConst>
      requires(sized_sentinel_for<sentinel_t</*maybe-const*/<Const, Views>>,
                                  iterator_t</*maybe-const*/<OtherConst, Views>>> &&
               ...)
    friend constexpr common_type_t<
      range_difference_t</*maybe-const*/<OtherConst, Views>>...>
    operator-(const /*sentinel*/& y, const /*iterator*/<OtherConst>& x);
  };
}

类模板 std::ranges::zip_transform_view

namespace std::ranges {
  template<move_constructible F, input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0) && is_object_v<F> &&
            regular_invocable<F&, range_reference_t<Views>...> &&
            /*can-reference*/<invoke_result_t<F&, range_reference_t<Views>...>>
  class zip_transform_view : public view_interface<zip_transform_view<F, Views...>>
  {
    /*movable-box*/<F> /*fun_*/; // 仅用于阐述
    zip_view<Views...> /*zip_*/; // 仅用于阐述

    using /*InnerView*/ = zip_view<Views...>; // 仅用于阐述
    template<bool Const>
    using /*ziperator*/ =
      iterator_t</*maybe-const*/<Const, /*InnerView*/>>; // 仅用于阐述
    template<bool Const>
    using /*zentinel*/ =
      sentinel_t</*maybe-const*/<Const, /*InnerView*/>>; // 仅用于阐述

    // 类模板 zip_transform_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述

    // 类模板 zip_transform_view::sentinel
    template<bool>
    class /*sentinel*/; // 仅用于阐述

  public:
    zip_transform_view() = default;

    constexpr explicit zip_transform_view(F fun, Views... views);

    constexpr auto begin() { return /*iterator*/<false>(*this, /*zip_*/.begin()); }

    constexpr auto begin() const
      requires range<const /*InnerView*/> &&
               regular_invocable<const F&, range_reference_t<const Views>...>
    {
      return /*iterator*/<true>(*this, /*zip_*/.begin());
    }

    constexpr auto end()
    {
      if constexpr (common_range</*InnerView*/>) {
        return /*iterator*/<false>(*this, /*zip_*/.end());
      } else {
        return /*sentinel*/<false>(/*zip_*/.end());
      }
    }

    constexpr auto end() const
      requires range<const /*InnerView*/> &&
               regular_invocable<const F&, range_reference_t<const Views>...>
    {
      if constexpr (common_range<const /*InnerView*/>) {
        return /*iterator*/<true>(*this, /*zip_*/.end());
      } else {
        return /*sentinel*/<true>(/*zip_*/.end());
      }
    }

    constexpr auto size()
      requires sized_range</*InnerView*/>
    {
      return /*zip_*/.size();
    }

    constexpr auto size() const
      requires sized_range<const /*InnerView*/>
    {
      return /*zip_*/.size();
    }
  };

  template<class F, class... Rs>
  zip_transform_view(F, Rs&&...) -> zip_transform_view<F, views::all_t<Rs>...>;
}

Class template std::ranges::zip_transform_view::iterator

namespace std::ranges {
  template<move_constructible F, input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0) && is_object_v<F> &&
            regular_invocable<F&, range_reference_t<Views>...> &&
            /*can-reference*/<invoke_result_t<F&, range_reference_t<Views>...>>
  template<bool Const>
  class zip_transform_view<F, Views...>::/*iterator*/
  {
    using /*Parent*/ = /*maybe-const*/<Const, zip_transform_view>; // 仅用于阐述
    using /*Base*/   = /*maybe-const*/<Const, /*InnerView*/>;      // 仅用于阐述
    /*Parent*/* /*parent_*/ = nullptr;                             // 仅用于阐述
    /*ziperator*/<Const> /*inner_*/;                               // 仅用于阐述

    constexpr /*iterator*/(/*Parent*/& parent,
                           /*ziperator*/<Const> inner); // 仅用于阐述

  public:
    using iterator_category = /* 见描述 */; // 不总存在
    using iterator_concept  = typename /*ziperator*/<Const>::iterator_concept;
    using value_type        = remove_cvref_t<
      invoke_result_t</*maybe-const*/<Const, F>&,
                      range_reference_t</*maybe-const*/<Const, Views>>...>>;
    using difference_type = range_difference_t</*Base*/>;

    /*iterator*/()        = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to</*ziperator*/<false>, /*ziperator*/<Const>>;

    constexpr decltype(auto) operator*() const noexcept(/* 见描述 */);
    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires forward_range</*Base*/>;

    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;

    constexpr /*iterator*/& operator+=(difference_type x)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires random_access_range</*Base*/>;

    constexpr decltype(auto) operator[](difference_type n) const
      requires random_access_range</*Base*/>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires equality_comparable</*ziperator*/<Const>>;

    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type n, const /*iterator*/& i)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires sized_sentinel_for</*ziperator*/<Const>, /*ziperator*/<Const>>;
  };
}

类模板 std::ranges::zip_transform_view::sentinel

namespace std::ranges {
  template<move_constructible F, input_range... Views>
    requires(view<Views> && ...) && (sizeof...(Views) > 0) && is_object_v<F> &&
            regular_invocable<F&, range_reference_t<Views>...> &&
            /*can-reference*/<invoke_result_t<F&, range_reference_t<Views>...>>
  template<bool Const>
  class zip_transform_view<F, Views...>::/*sentinel*/
  {
    /*zentinel*/<Const> /*inner_*/;                             // 仅用于阐述
    constexpr explicit /*sentinel*/(/*zentinel*/<Const> inner); // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr /*sentinel*/(/*sentinel*/<!Const> i)
      requires Const && convertible_to</*zentinel*/<false>, /*zentinel*/<Const>>;

    template<bool OtherConst>
      requires sentinel_for</*zentinel*/<Const>, /*ziperator*/<OtherConst>>
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for</*zentinel*/<Const>, /*ziperator*/<OtherConst>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, /*InnerView*/>>
    operator-(const /*iterator*/<OtherConst>& x, const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for</*zentinel*/<Const>, /*ziperator*/<OtherConst>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, /*InnerView*/>>
    operator-(const /*sentinel*/& x, const /*iterator*/<OtherConst>& y);
  };
}

类模板 std::ranges::adjacent_view

namespace std::ranges {
  template<forward_range V, size_t N>
    requires view<V> && (N > 0)
  class adjacent_view : public view_interface<adjacent_view<V, N>>
  {
    V /*base_*/ = V(); // 仅用于阐述

    // 类模板 adjacent_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述

    // 类模板 adjacent_view::sentinel
    template<bool>
    class /*sentinel*/; // 仅用于阐述

    struct /*as-sentinel*/
    {}; // 仅用于阐述

  public:
    adjacent_view()
      requires default_initializable<V>
    = default;
    constexpr explicit adjacent_view(V base);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      return /*iterator*/<false>(ranges::begin(/*base_*/), ranges::end(/*base_*/));
    }

    constexpr auto begin() const
      requires range<const V>
    {
      return /*iterator*/<true>(ranges::begin(/*base_*/), ranges::end(/*base_*/));
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (common_range<V>) {
        return /*iterator*/<false>(
          /*as-sentinel*/{}, ranges::begin(/*base_*/), ranges::end(/*base_*/));
      } else {
        return /*sentinel*/<false>(ranges::end(/*base_*/));
      }
    }

    constexpr auto end() const
      requires range<const V>
    {
      if constexpr (common_range<const V>) {
        return /*iterator*/<true>(
          /*as-sentinel*/{}, ranges::begin(/*base_*/), ranges::end(/*base_*/));
      } else {
        return /*sentinel*/<true>(ranges::end(/*base_*/));
      }
    }

    constexpr auto size()
      requires sized_range<V>;
    constexpr auto size() const
      requires sized_range<const V>;

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>;
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>;
  };
}

类模板 std::ranges::adjacent_view::iterator

namespace std::ranges {
  template<forward_range V, size_t N>
    requires view<V> && (N > 0)
  template<bool Const>
  class adjacent_view<V, N>::/*iterator*/
  {
    using /*Base*/ = /*maybe-const*/<Const, V>; // 仅用于阐述
    array<iterator_t</*Base*/>, N> /*current_*/ =
      array<iterator_t</*Base*/>, N>(); // 仅用于阐述
    constexpr /*iterator*/(iterator_t</*Base*/> first,
                           sentinel_t</*Base*/> last); // 仅用于阐述
    constexpr /*iterator*/(/*as-sentinel*/,
                           iterator_t</*Base*/> first,
                           iterator_t</*Base*/> last);
    // 仅用于阐述
  public:
    using iterator_category = input_iterator_tag;
    using iterator_concept  = /* 见描述 */;
    using value_type        = tuple</*REPEAT*/(range_value_t</*Base*/>, N)...>;
    using difference_type   = range_difference_t</*Base*/>;

    /*iterator*/()          = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>>;

    constexpr auto operator*() const;
    constexpr /*iterator*/& operator++();
    constexpr /*iterator*/ operator++(int);

    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;

    constexpr /*iterator*/& operator+=(difference_type x)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires random_access_range</*Base*/>;

    constexpr auto operator[](difference_type n) const
      requires random_access_range</*Base*/>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y);
    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/> && three_way_comparable<iterator_t</*Base*/>>
    ;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type n, const /*iterator*/& i)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires sized_sentinel_for<iterator_t</*Base*/>, iterator_t</*Base*/>>;

    friend constexpr auto iter_move(const /*iterator*/& i) noexcept(
      /* 见描述 */);
    friend constexpr void iter_swap(const /*iterator*/& l,
                                    const /*iterator*/& r) noexcept(/* 见描述 */)
      requires indirectly_swappable<iterator_t</*Base*/>>;
  };
}

类模板 std::ranges::adjacent_view::sentinel

namespace std::ranges {
  template<forward_range V, size_t N>
    requires view<V> && (N > 0)
  template<bool Const>
  class adjacent_view<V, N>::/*sentinel*/
  {
    using /*Base*/                = /*maybe-const*/<Const, V>; // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/ = sentinel_t</*Base*/>();    // 仅用于阐述
    constexpr explicit /*sentinel*/(sentinel_t</*Base*/> end); // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr /*sentinel*/(/*sentinel*/<!Const> i)
      requires Const && convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    template<bool OtherConst>
      requires sentinel_for<sentinel_t</*Base*/>,
                            iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for<sentinel_t</*Base*/>,
                                  iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, V>> operator-(
      const /*iterator*/<OtherConst>& x,
      const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for<sentinel_t</*Base*/>,
                                  iterator_t</*maybe-const*/<OtherConst, V>>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, V>> operator-(
      const /*sentinel*/& y,
      const /*iterator*/<OtherConst>& x);
  };
}

类模板 std::ranges::adjacent_transform_view

namespace std::ranges {
  template<forward_range V, move_constructible F, size_t N>
    requires view<V> && (N > 0) && is_object_v<F> &&
             regular_invocable<F&, /*REPEAT*/(range_reference_t<V>, N)...> &&
             /*can-reference*/<
               invoke_result_t<F&, /*REPEAT*/(range_reference_t<V>, N)...>>
  class adjacent_transform_view : public view_interface<adjacent_transform_view<V, F, N>>
  {
    /*movable-box*/<F> /*fun_*/;    // 仅用于阐述
    adjacent_view<V, N> /*inner_*/; // 仅用于阐述

    using /*InnerView*/ = adjacent_view<V, N>; // 仅用于阐述
    template<bool Const>
    using /*inner-iterator*/ =
      iterator_t</*maybe-const*/<Const, /*InnerView*/>>; // 仅用于阐述
    template<bool Const>
    using /*inner-sentinel*/ =
      sentinel_t</*maybe-const*/<Const, /*InnerView*/>>; // 仅用于阐述

    // 类模板 adjacent_transform_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述

    // 类模板 adjacent_transform_view::sentinel
    template<bool>
    class /*sentinel*/; // 仅用于阐述

  public:
    adjacent_transform_view() = default;
    constexpr explicit adjacent_transform_view(V base, F fun);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*inner_*/.base();
    }
    constexpr V base() && { return std::move(/*inner_*/).base(); }

    constexpr auto begin() { return /*iterator*/<false>(*this, /*inner_*/.begin()); }

    constexpr auto begin() const
      requires range<const /*InnerView*/> &&
               regular_invocable<const F&, /*REPEAT*/(range_reference_t<const V>, N)...>
    {
      return /*iterator*/<true>(*this, /*inner_*/.begin());
    }

    constexpr auto end()
    {
      if constexpr (common_range</*InnerView*/>) {
        return /*iterator*/<false>(*this, /*inner_*/.end());
      } else {
        return /*sentinel*/<false>(/*inner_*/.end());
      }
    }

    constexpr auto end() const
      requires range<const /*InnerView*/> &&
               regular_invocable<const F&, /*REPEAT*/(range_reference_t<const V>, N)...>
    {
      if constexpr (common_range<const /*InnerView*/>) {
        return /*iterator*/<true>(*this, /*inner_*/.end());
      } else {
        return /*sentinel*/<true>(/*inner_*/.end());
      }
    }

    constexpr auto size()
      requires sized_range</*InnerView*/>
    {
      return /*inner_*/.size();
    }

    constexpr auto size() const
      requires sized_range<const /*InnerView*/>
    {
      return /*inner_*/.size();
    }

    constexpr auto reserve_hint()
      requires approximately_sized_range</*InnerView*/>
    {
      return /*inner_*/.reserve_hint();
    }

    constexpr auto reserve_hint() const
      requires approximately_sized_range<const /*InnerView*/>
    {
      return /*inner_*/.reserve_hint();
    }
  };
}

类模板 std::ranges::adjacent_transform_view::iterator

namespace std::ranges {
  template<forward_range V, move_constructible F, size_t N>
    requires view<V> && (N > 0) && is_object_v<F> &&
             regular_invocable<F&, /*REPEAT*/(range_reference_t<V>, N)...> &&
             /*can-reference*/<
               invoke_result_t<F&, /*REPEAT*/(range_reference_t<V>, N)...>>
  template<bool Const>
  class adjacent_transform_view<V, F, N>::/*iterator*/
  {
    using /*Parent*/ = /*maybe-const*/<Const, adjacent_transform_view>; // 仅用于阐述
    using /*Base*/   = /*maybe-const*/<Const, V>;                       // 仅用于阐述
    /*Parent*/* /*parent_*/ = nullptr;                                  // 仅用于阐述
    /*inner-iterator*/<Const> /*inner_*/;                               // 仅用于阐述

    constexpr /*iterator*/(/*Parent*/& parent,
                           /*inner-iterator*/<Const> inner); // 仅用于阐述

  public:
    using iterator_category = /* 见描述 */;
    using iterator_concept  = typename /*inner-iterator*/<Const>::iterator_concept;
    using value_type =
      remove_cvref_t<invoke_result_t</*maybe-const*/<Const, F>&,
                                     /*REPEAT*/(range_reference_t</*Base*/>, N)...>>;
    using difference_type = range_difference_t</*Base*/>;

    /*iterator*/()        = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const
               && convertible_to</*inner-iterator*/<false>, /*inner-iterator*/<Const>>;

    constexpr decltype(auto) operator*() const noexcept(/* 见描述 */);
    constexpr /*iterator*/& operator++();
    constexpr /*iterator*/ operator++(int);
    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/& operator+=(difference_type x)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires random_access_range</*Base*/>;

    constexpr decltype(auto) operator[](difference_type n) const
      requires random_access_range</*Base*/>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y);
    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/> &&
               three_way_comparable</*inner-iterator*/<Const>>;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type n, const /*iterator*/& i)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires sized_sentinel_for</*inner-iterator*/<Const>, /*inner-iterator*/<Const>>;
  };
}

类模板 std::ranges::adjacent_transform_view::sentinel

namespace std::ranges {
  template<forward_range V, move_constructible F, size_t N>
    requires view<V> && (N > 0) && is_object_v<F> &&
             regular_invocable<F&, /*REPEAT*/(range_reference_t<V>, N)...> &&
             /*can-reference*/<
               invoke_result_t<F&, /*REPEAT*/(range_reference_t<V>, N)...>>
  template<bool Const>
  class adjacent_transform_view<V, F, N>::/*sentinel*/
  {
    /*inner-sentinel*/<Const> /*inner_*/;                             // 仅用于阐述
    constexpr explicit /*sentinel*/(/*inner-sentinel*/<Const> inner); // 仅用于阐述

  public:
    /*sentinel*/() = default;
    constexpr /*sentinel*/(/*sentinel*/<!Const> i)
      requires Const
               && convertible_to</*inner-sentinel*/<false>, /*inner-sentinel*/<Const>>;

    template<bool OtherConst>
      requires sentinel_for</*inner-sentinel*/<Const>, /*inner-iterator*/<OtherConst>>
    friend constexpr bool operator==(const /*iterator*/<OtherConst>& x,
                                     const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for</*inner-sentinel*/<Const>,
                                  /*inner-iterator*/<OtherConst>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, /*InnerView*/>>
    operator-(const /*iterator*/<OtherConst>& x, const /*sentinel*/& y);

    template<bool OtherConst>
      requires sized_sentinel_for</*inner-sentinel*/<Const>,
                                  /*inner-iterator*/<OtherConst>>
    friend constexpr range_difference_t</*maybe-const*/<OtherConst, /*InnerView*/>>
    operator-(const /*sentinel*/& x, const /*iterator*/<OtherConst>& y);
  };
}

类模板 std::ranges::chunk_view for input_ranges

namespace std::ranges {
  template<class I>
  constexpr I /*div-ceil*/(I num, I denom)
  { // 仅用于阐述
    I r = num / denom;
    if (num % denom)
      ++r;
    return r;
  }

  template<view V>
    requires input_range<V>
  class chunk_view : public view_interface<chunk_view<V>>
  {
    V /*base_*/;                              // 仅用于阐述
    range_difference_t<V> /*n_*/;             // 仅用于阐述
    range_difference_t<V> /*remainder_*/ = 0; // 仅用于阐述

    /*non-propagating-cache*/<iterator_t<V>> /*current_*/; // 仅用于阐述

    // 类 chunk_view::outer-iterator
    class /*outer-iterator*/; // 仅用于阐述

    // 类 chunk_view::inner-iterator
    class /*inner-iterator*/; // 仅用于阐述

  public:
    constexpr explicit chunk_view(V base, range_difference_t<V> n);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr /*outer-iterator*/ begin();
    constexpr default_sentinel_t end() const noexcept;

    constexpr auto size()
      requires sized_range<V>;
    constexpr auto size() const
      requires sized_range<const V>;

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>;
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>;
  };

  template<class R>
  chunk_view(R&&, range_difference_t<R>) -> chunk_view<views::all_t<R>>;
}

类模板 std::ranges::chunk_view::outer_iterator for input_ranges

namespace std::ranges {
  template<view V>
    requires input_range<V>
  class chunk_view<V>::/*outer-iterator*/
  {
    chunk_view* /*parent_*/; // 仅用于阐述

    constexpr explicit /*outer-iterator*/(chunk_view& parent); // 仅用于阐述

  public:
    using iterator_concept = input_iterator_tag;
    using difference_type  = range_difference_t<V>;

    // 类 chunk_view::outer-iterator::value_type
    struct value_type;

    /*outer-iterator*/(/*outer-iterator*/&&)            = default;
    /*outer-iterator*/& operator=(/*outer-iterator*/&&) = default;

    constexpr value_type operator*() const;
    constexpr /*outer-iterator*/& operator++();
    constexpr void operator++(int);

    friend constexpr bool operator==(const /*outer-iterator*/& x, default_sentinel_t);

    friend constexpr difference_type operator-(default_sentinel_t y,
                                               const /*outer-iterator*/& x)
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
    friend constexpr difference_type operator-(const /*outer-iterator*/& x,
                                               default_sentinel_t y)
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
  };
}

类模板 std::ranges::chunk_view::outer_iterator::value_type for input_ranges

namespace std::ranges {
  template<view V>
    requires input_range<V>
  struct chunk_view<V>::/*outer-iterator*/::value_type : view_interface<value_type>
  {
  private:
    chunk_view* /*parent_*/; // 仅用于阐述

    constexpr explicit value_type(chunk_view& parent); // 仅用于阐述

  public:
    constexpr /*inner-iterator*/ begin() const noexcept;
    constexpr default_sentinel_t end() const noexcept;

    constexpr auto size() const
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
  };
}

类模板 std::ranges::chunk_view::inner_iterator for input_ranges

namespace std::ranges {
  template<view V>
    requires input_range<V>
  class chunk_view<V>::/*inner-iterator*/
  {
    chunk_view* /*parent_*/; // 仅用于阐述

    constexpr explicit /*inner-iterator*/(chunk_view& parent) noexcept; // 仅用于阐述

  public:
    using iterator_concept                              = input_iterator_tag;
    using difference_type                               = range_difference_t<V>;
    using value_type                                    = range_value_t<V>;

    /*inner-iterator*/(/*inner-iterator*/&&)            = default;
    /*inner-iterator*/& operator=(/*inner-iterator*/&&) = default;

    constexpr const iterator_t<V>& base() const&;

    constexpr range_reference_t<V> operator*() const;
    constexpr /*inner-iterator*/& operator++();
    constexpr void operator++(int);

    friend constexpr bool operator==(const /*inner-iterator*/& x, default_sentinel_t);

    friend constexpr difference_type operator-(default_sentinel_t y,
                                               const /*inner-iterator*/& x)
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
    friend constexpr difference_type operator-(const /*inner-iterator*/& x,
                                               default_sentinel_t y)
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;

    friend constexpr range_rvalue_reference_t<V>
    iter_move(const /*inner-iterator*/& i) noexcept(
      noexcept(ranges::iter_move(*i./*parent_*/->/*current_*/)));

    friend constexpr void
    iter_swap(const /*inner-iterator*/& x, const /*inner-iterator*/& y) noexcept(noexcept(
      ranges::iter_swap(*x./*parent_*/->/*current_*/, *y./*parent_*/->/*current_*/)))
      requires indirectly_swappable<iterator_t<V>>;
  };
}

Class template std::ranges::chunk_view for forward_ranges

namespace std::ranges {
  template<view V>
    requires forward_range<V>
  class chunk_view<V> : public view_interface<chunk_view<V>>
  {
    V /*base_*/;                  // 仅用于阐述
    range_difference_t<V> /*n_*/; // 仅用于阐述

    // 类模板 chunk_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述

  public:
    constexpr explicit chunk_view(V base, range_difference_t<V> n);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      return /*iterator*/<false>(this, ranges::begin(/*base_*/));
    }

    constexpr auto begin() const
      requires forward_range<const V>
    {
      return /*iterator*/<true>(this, ranges::begin(/*base_*/));
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (common_range<V> && sized_range<V>) {
        auto missing = (/*n_*/ - ranges::distance(/*base_*/) % /*n_*/) % /*n_*/;
        return /*iterator*/<false>(this, ranges::end(/*base_*/), missing);
      } else if constexpr (common_range<V> && !bidirectional_range<V>) {
        return /*iterator*/<false>(this, ranges::end(/*base_*/));
      } else {
        return default_sentinel;
      }
    }

    constexpr auto end() const
      requires forward_range<const V>
    {
      if constexpr (common_range<const V> && sized_range<const V>) {
        auto missing = (/*n_*/ - ranges::distance(/*base_*/) % /*n_*/) % /*n_*/;
        return /*iterator*/<true>(this, ranges::end(/*base_*/), missing);
      } else if constexpr (common_range<const V> && !bidirectional_range<const V>) {
        return /*iterator*/<true>(this, ranges::end(/*base_*/));
      } else {
        return default_sentinel;
      }
    }

    constexpr auto size()
      requires sized_range<V>;
    constexpr auto size() const
      requires sized_range<const V>;

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>;
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>;
  };
}

类模板 std::ranges::chunk_view::iterator for forward_ranges

namespace std::ranges {
  template<view V>
    requires forward_range<V>
  template<bool Const>
  class chunk_view<V>::/*iterator*/
  {
    using /*Parent*/ = /*maybe-const*/<Const, chunk_view>; // 仅用于阐述
    using /*Base*/   = /*maybe-const*/<Const, V>;          // 仅用于阐述

    iterator_t</*Base*/> /*current_*/         = iterator_t</*Base*/>(); // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/             = sentinel_t</*Base*/>(); // 仅用于阐述
    range_difference_t</*Base*/> /*n_*/       = 0;                      // 仅用于阐述
    range_difference_t</*Base*/> /*missing_*/ = 0;                      // 仅用于阐述

    constexpr /*iterator*/(/*Parent*/* parent,
                           iterator_t</*Base*/> current, // 仅用于阐述
                           range_difference_t</*Base*/> missing = 0);

  public:
    using iterator_category = input_iterator_tag;
    using iterator_concept  = /* 见描述 */;
    using value_type = decltype(views::take(subrange(/*current_*/, /*end_*/), /*n_*/));
    using difference_type = range_difference_t</*Base*/>;

    /*iterator*/()        = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>> &&
               convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    constexpr iterator_t</*Base*/> base() const;

    constexpr value_type operator*() const;
    constexpr /*iterator*/& operator++();
    constexpr /*iterator*/ operator++(int);

    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;

    constexpr /*iterator*/& operator+=(difference_type x)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires random_access_range</*Base*/>;

    constexpr value_type operator[](difference_type n) const
      requires random_access_range</*Base*/>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y);
    friend constexpr bool operator==(const /*iterator*/& x, default_sentinel_t);

    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/> && three_way_comparable<iterator_t</*Base*/>>
    ;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type n, const /*iterator*/& i)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires sized_sentinel_for<iterator_t</*Base*/>, iterator_t</*Base*/>>;

    friend constexpr difference_type operator-(default_sentinel_t y,
                                               const /*iterator*/& x)
      requires sized_sentinel_for<sentinel_t</*Base*/>, iterator_t</*Base*/>>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               default_sentinel_t y)
      requires sized_sentinel_for<sentinel_t</*Base*/>, iterator_t</*Base*/>>;
  };
}

类模板 std::ranges::slide_view

namespace std::ranges {
  template<class V>
  concept /*slide-caches-nothing*/ =
    random_access_range<V> && sized_range<V>; // 仅用于阐述

  template<class V>
  concept /*slide-caches-last*/ = // 仅用于阐述
    !/*slide-caches-nothing*/<V> && bidirectional_range<V> && common_range<V>;

  template<class V>
  concept /*slide-caches-first*/ = // 仅用于阐述
    !/*slide-caches-nothing*/<V> && !/*slide-caches-last*/<V>;

  template<forward_range V>
    requires view<V>
  class slide_view : public view_interface<slide_view<V>>
  {
    V /*base_*/;                  // 仅用于阐述
    range_difference_t<V> /*n_*/; // 仅用于阐述

    // 类模板 slide_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述

    // 类 slide_view::sentinel
    class /*sentinel*/; // 仅用于阐述

  public:
    constexpr explicit slide_view(V base, range_difference_t<V> n);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!(/*simple-view*/<V> && /*slide-caches-nothing*/<const V>));
    constexpr auto begin() const
      requires /*slide-caches-nothing*/<const V>;

    constexpr auto end()
      requires(!(/*simple-view*/<V> && /*slide-caches-nothing*/<const V>));
    constexpr auto end() const
      requires /*slide-caches-nothing*/<const V>;

    constexpr auto size()
      requires sized_range<V>;
    constexpr auto size() const
      requires sized_range<const V>;

    constexpr auto reserve_hintsize()
      requires approximately_sized_range<V>;
    constexpr auto reserve_hintsize() const
      requires approximately_sized_range<const V>;
  };

  template<class R>
  slide_view(R&&, range_difference_t<R>) -> slide_view<views::all_t<R>>;
}

类模板 std::ranges::slide_view::iterator

namespace std::ranges {
  template<forward_range V>
    requires view<V>
  template<bool Const>
  class slide_view<V>::/*iterator*/
  {
    using /*Base*/                    = /*maybe-const*/<Const, V>; // 仅用于阐述
    iterator_t</*Base*/> /*current_*/ = iterator_t</*Base*/>();    // 仅用于阐述
    iterator_t</*Base*/> /*last-ele_*/ =
      iterator_t</*Base*/>(); // 仅用于阐述
                              // 仅当 Base 实现 slide-caches-first 时存在
    range_difference_t</*Base*/> /*n_*/ = 0; // 仅用于阐述

    constexpr /*iterator*/(iterator_t</*Base*/> current,
                           range_difference_t</*Base*/> n) // 仅用于阐述
      requires(!/*slide-caches-first*/</*Base*/>);

    constexpr /*iterator*/(iterator_t</*Base*/> current,
                           iterator_t</*Base*/> last_ele, // 仅用于阐述
                           range_difference_t</*Base*/> n)
      requires /*slide-caches-first*/</*Base*/>;

  public:
    using iterator_category = input_iterator_tag;
    using iterator_concept  = /* 见描述 */;
    using value_type        = decltype(views::counted(/*current_*/, /*n_*/));
    using difference_type   = range_difference_t</*Base*/>;

    /*iterator*/()          = default;
    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>>;

    constexpr auto operator*() const;
    constexpr /*iterator*/& operator++();
    constexpr /*iterator*/ operator++(int);

    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;

    constexpr /*iterator*/& operator+=(difference_type x)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires random_access_range</*Base*/>;

    constexpr auto operator[](difference_type n) const
      requires random_access_range</*Base*/>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y);

    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;
    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/> && three_way_comparable<iterator_t</*Base*/>>
    ;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type n, const /*iterator*/& i)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& i, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires sized_sentinel_for<iterator_t</*Base*/>, iterator_t</*Base*/>>;
  };
}

类模板 std::ranges::slide_view::sentinel

namespace std::ranges {
  template<forward_range V>
    requires view<V>
  class slide_view<V>::/*sentinel*/
  {
    sentinel_t<V> /*end_*/ = sentinel_t<V>();           // 仅用于阐述
    constexpr explicit /*sentinel*/(sentinel_t<V> end); // 仅用于阐述

  public:
    /*sentinel*/() = default;

    friend constexpr bool operator==(const /*iterator*/<false>& x, const /*sentinel*/& y);

    friend constexpr range_difference_t<V> operator-(const /*iterator*/<false>& x,
                                                     const /*sentinel*/& y)
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;

    friend constexpr range_difference_t<V> operator-(const /*sentinel*/& y,
                                                     const /*iterator*/<false>& x)
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
  };
}

类模板 std::ranges::chunk_by_view

namespace std::ranges {
  template<forward_range V, indirect_binary_predicate<iterator_t<V>, iterator_t<V>> Pred>
    requires view<V> && is_object_v<Pred>
  class chunk_by_view : public view_interface<chunk_by_view<V, Pred>>
  {
    V /*base_*/ = V();               // 仅用于阐述
    /*movable-box*/<Pred> /*pred_*/; // 仅用于阐述

    // 类 chunk_by_view::iterator
    class /*iterator*/; // 仅用于阐述

  public:
    chunk_by_view()
      requires default_initializable<V> && default_initializable<Pred>
    = default;
    constexpr explicit chunk_by_view(V base, Pred pred);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr const Pred& pred() const;

    constexpr /*iterator*/ begin();
    constexpr auto end();

    constexpr iterator_t<V> /*find-next*/(iterator_t<V>); // 仅用于阐述
    constexpr iterator_t<V> /*find-prev*/(iterator_t<V>)  // 仅用于阐述
      requires bidirectional_range<V>;
  };

  template<class R, class Pred>
  chunk_by_view(R&&, Pred) -> chunk_by_view<views::all_t<R>, Pred>;
}

类模板 std::ranges::chunk_by_view::iterator

namespace std::ranges {
  template<forward_range V, indirect_binary_predicate<iterator_t<V>, iterator_t<V>> Pred>
    requires view<V> && is_object_v<Pred>
  class chunk_by_view<V, Pred>::/*iterator*/
  {
    chunk_by_view* /*parent_*/ = nullptr;         // 仅用于阐述
    iterator_t<V> /*current_*/ = iterator_t<V>(); // 仅用于阐述
    iterator_t<V> /*next_*/    = iterator_t<V>(); // 仅用于阐述

    constexpr /*iterator*/(chunk_by_view& parent,
                           iterator_t<V> current, // 仅用于阐述
                           iterator_t<V> next);

  public:
    using value_type        = subrange<iterator_t<V>>;
    using difference_type   = range_difference_t<V>;
    using iterator_category = input_iterator_tag;
    using iterator_concept  = /* 见描述 */;

    /*iterator*/()          = default;

    constexpr value_type operator*() const;
    constexpr /*iterator*/& operator++();
    constexpr /*iterator*/ operator++(int);

    constexpr /*iterator*/& operator--()
      requires bidirectional_range<V>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range<V>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y);
    friend constexpr bool operator==(const /*iterator*/& x, default_sentinel_t);
  };
}

类模板 std::ranges::stride_view

namespace std::ranges {
  template<input_range V>
    requires view<V>
  class stride_view : public view_interface<stride_view<V>>
  {
    V /*base_*/;                       // 仅用于阐述
    range_difference_t<V> /*stride_*/; // 仅用于阐述
    // 类模板 stride_view::iterator
    template<bool>
    class /*iterator*/; // 仅用于阐述
  public:
    constexpr explicit stride_view(V base, range_difference_t<V> stride);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr range_difference_t<V> stride() const noexcept;

    constexpr auto begin()
      requires(!/*simple-view*/<V>)
    {
      return /*iterator*/<false>(this, ranges::begin(/*base_*/));
    }

    constexpr auto begin() const
      requires range<const V>
    {
      return /*iterator*/<true>(this, ranges::begin(/*base_*/));
    }

    constexpr auto end()
      requires(!/*simple-view*/<V>)
    {
      if constexpr (common_range<V> && sized_range<V> && forward_range<V>) {
        auto missing =
          (/*stride_*/ - ranges::distance(/*base_*/) % /*stride_*/) % /*stride_*/;
        return /*iterator*/<false>(this, ranges::end(/*base_*/), missing);
      } else if constexpr (common_range<V> && !bidirectional_range<V>) {
        return /*iterator*/<false>(this, ranges::end(/*base_*/));
      } else {
        return default_sentinel;
      }
    }

    constexpr auto end() const
      requires range<const V>
    {
      if constexpr (common_range<const V> && sized_range<const V> &&
                    forward_range<const V>) {
        auto missing =
          (/*stride_*/ - ranges::distance(/*base_*/) % /*stride_*/) % /*stride_*/;
        return /*iterator*/<true>(this, ranges::end(/*base_*/), missing);
      } else if constexpr (common_range<const V> && !bidirectional_range<const V>) {
        return /*iterator*/<true>(this, ranges::end(/*base_*/));
      } else {
        return default_sentinel;
      }
    }

    constexpr auto size()
      requires sized_range<V>;
    constexpr auto size() const
      requires sized_range<const V>;

    constexpr auto reserve_hint()
      requires approximately_sized_range<V>;
    constexpr auto reserve_hint() const
      requires approximately_sized_range<const V>;
  };

  template<class R>
  stride_view(R&&, range_difference_t<R>) -> stride_view<views::all_t<R>>;
}

类模板 std::ranges::stride_view::iterator

namespace std::ranges {
  template<input_range V>
    requires view<V>
  template<bool Const>
  class stride_view<V>::/*iterator*/
  {
    using /*Parent*/ = /*maybe-const*/<Const, stride_view>; // 仅用于阐述
    using /*Base*/   = /*maybe-const*/<Const, V>;           // 仅用于阐述

    iterator_t</*Base*/> /*current_*/         = iterator_t</*Base*/>(); // 仅用于阐述
    sentinel_t</*Base*/> /*end_*/             = sentinel_t</*Base*/>(); // 仅用于阐述
    range_difference_t</*Base*/> /*stride_*/  = 0;                      // 仅用于阐述
    range_difference_t</*Base*/> /*missing_*/ = 0;                      // 仅用于阐述

    constexpr /*iterator*/(/*Parent*/* parent,
                           iterator_t</*Base*/> current, // 仅用于阐述
                           range_difference_t</*Base*/> missing = 0);

  public:
    using difference_type   = range_difference_t</*Base*/>;
    using value_type        = range_value_t</*Base*/>;
    using iterator_concept  = /* 见描述 */;
    using iterator_category = /* 见描述 */; // 不总存在

    /*iterator*/()
      requires default_initializable<iterator_t</*Base*/>>
    = default;

    constexpr /*iterator*/(/*iterator*/<!Const> other)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>> &&
               convertible_to<sentinel_t<V>, sentinel_t</*Base*/>>;

    constexpr iterator_t</*Base*/> base() &&;
    constexpr const iterator_t</*Base*/>& base() const& noexcept;

    constexpr decltype(auto) operator*() const { return */*current_*/; }

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires forward_range</*Base*/>;

    constexpr /*iterator*/& operator--()
      requires bidirectional_range</*Base*/>;
    constexpr /*iterator*/ operator--(int)
      requires bidirectional_range</*Base*/>;

    constexpr /*iterator*/& operator+=(difference_type n)
      requires random_access_range</*Base*/>;
    constexpr /*iterator*/& operator-=(difference_type n)
      requires random_access_range</*Base*/>;

    constexpr decltype(auto) operator[](difference_type n) const
      requires random_access_range</*Base*/>
    {
      return *(*this + n);
    }

    friend constexpr bool operator==(const /*iterator*/& x, default_sentinel_t);

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires equality_comparable<iterator_t</*Base*/>>;

    friend constexpr bool operator<(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;

    friend constexpr bool operator>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;

    friend constexpr bool operator<=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;

    friend constexpr bool operator>=(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/>;

    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires random_access_range</*Base*/> && three_way_comparable<iterator_t</*Base*/>>
    ;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& x, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator+(difference_type n, const /*iterator*/& x)
      requires random_access_range</*Base*/>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& x, difference_type n)
      requires random_access_range</*Base*/>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires sized_sentinel_for<iterator_t</*Base*/>, iterator_t</*Base*/>>;

    friend constexpr difference_type operator-(default_sentinel_t y,
                                               const /*iterator*/& x)
      requires sized_sentinel_for<sentinel_t</*Base*/>, iterator_t</*Base*/>>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               default_sentinel_t y)
      requires sized_sentinel_for<sentinel_t</*Base*/>, iterator_t</*Base*/>>;

    friend constexpr range_rvalue_reference_t</*Base*/> iter_move(
      const /*iterator*/& i) noexcept(noexcept(ranges::iter_move(i./*current_*/)));

    friend constexpr void iter_swap(
      const /*iterator*/& x,
      const /*iterator*/& y) noexcept(noexcept(ranges::iter_swap(x./*current_*/,
                                                                 y./*current_*/)))
      requires indirectly_swappable<iterator_t</*Base*/>>;
  };
}

类模板 std::ranges::cartesian_product_view

namespace std::ranges {
  template<bool Const, class First, class... Vs>
  concept /*cartesian-product-is-random-access*/ = // 仅用于阐述
    (random_access_range</*maybe-const*/<Const, First>> && ... &&
     (random_access_range</*maybe-const*/<Const, Vs>> &&
      sized_range</*maybe-const*/<Const, Vs>>));

  template<class R>
  concept /*cartesian-product-common-arg*/ = // 仅用于阐述
    common_range<R> || (sized_range<R> && random_access_range<R>);

  template<bool Const, class First, class... Vs>
  concept /*cartesian-product-is-bidirectional*/ = // 仅用于阐述
    (bidirectional_range</*maybe-const*/<Const, First>> && ... &&
     (bidirectional_range</*maybe-const*/<Const, Vs>> &&
      /*cartesian-product-common-arg*/</*maybe-const*/<Const, Vs>>));

  template<class First, class...>
  concept /*cartesian-product-is-common*/ = // 仅用于阐述
    /*cartesian-product-common-arg*/<First>;

  template<class... Vs>
  concept /*cartesian-product-is-sized*/ = // 仅用于阐述
    (sized_range<Vs> && ...);

  template<bool Const, template<class> class FirstSent, class First, class... Vs>
  concept /*cartesian-is-sized-sentinel*/ = // 仅用于阐述
    (sized_sentinel_for<FirstSent</*maybe-const*/<Const, First>>,
                        iterator_t</*maybe-const*/<Const, First>>> &&
     ... &&
     (sized_range</*maybe-const*/<Const, Vs>> &&
      sized_sentinel_for<iterator_t</*maybe-const*/<Const, Vs>>,
                         iterator_t</*maybe-const*/<Const, Vs>>>));

  template</*cartesian-product-common-arg*/ R>
  constexpr auto /*cartesian-common-arg-end*/(R& r)
  { // 仅用于阐述
    if constexpr (common_range<R>) {
      return ranges::end(r);
    } else {
      return ranges::begin(r) + ranges::distance(r);
    }
  }

  template<input_range First, forward_range... Vs>
    requires(view<First> && ... && view<Vs>)
  class cartesian_product_view
    : public view_interface<cartesian_product_view<First, Vs...>>
  {
  private:
    tuple<First, Vs...> /*bases_*/; // 仅用于阐述
    // 类模板 cartesian_product_view::iterator
    template<bool Const>
    class /*iterator*/; // 仅用于阐述

  public:
    constexpr cartesian_product_view() = default;
    constexpr explicit cartesian_product_view(First first_base, Vs... bases);

    constexpr /*iterator*/<false> begin()
      requires(!/*simple-view*/<First> || ... || !/*simple-view*/<Vs>);
    constexpr /*iterator*/<true> begin() const
      requires(range<const First> && ... && range<const Vs>);

    constexpr /*iterator*/<false> end()
      requires((!/*simple-view*/<First> || ... || !/*simple-view*/<Vs>) &&
               /*cartesian-product-is-common*/<First, Vs...>);
    constexpr /*iterator*/<true> end() const
      requires /*cartesian-product-is-common*/<const First, const Vs...>;
    constexpr default_sentinel_t end() const noexcept;

    constexpr /* 见描述 */ size()
      requires /*cartesian-product-is-sized*/<First, Vs...>;
    constexpr /* 见描述 */ size() const
      requires /*cartesian-product-is-sized*/<const First, const Vs...>;
  };

  template<class... Vs>
  cartesian_product_view(Vs&&...) -> cartesian_product_view<views::all_t<Vs>...>;
}

类模板 std::ranges::cartesian_product_view::iterator

namespace std::ranges {
  template<input_range First, forward_range... Vs>
    requires(view<First> && ... && view<Vs>)
  template<bool Const>
  class cartesian_product_view<First, Vs...>::/*iterator*/
  {
  public:
    using iterator_category = input_iterator_tag;
    using iterator_concept  = /* 见描述 */;
    using value_type        = tuple<range_value_t</*maybe-const*/<Const, First>>,
                             range_value_t</*maybe-const*/<Const, Vs>>...>;
    using reference         = tuple<range_reference_t</*maybe-const*/<Const, First>>,
                            range_reference_t</*maybe-const*/<Const, Vs>>...>;
    using difference_type   = /* 见描述 */;

    /*iterator*/()          = default;

    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && (convertible_to<iterator_t<First>, iterator_t<const First>> &&
                         ... && convertible_to<iterator_t<Vs>, iterator_t<const Vs>>);

    constexpr auto operator*() const;
    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);
    constexpr /*iterator*/ operator++(int)
      requires forward_range</*maybe-const*/<Const, First>>;

    constexpr /*iterator*/& operator--()
      requires /*cartesian-product-is-bidirectional*/<Const, First, Vs...>;
    constexpr /*iterator*/ operator--(int)
      requires /*cartesian-product-is-bidirectional*/<Const, First, Vs...>;

    constexpr /*iterator*/& operator+=(difference_type x)
      requires /*cartesian-product-is-random-access*/<Const, First, Vs...>;
    constexpr /*iterator*/& operator-=(difference_type x)
      requires /*cartesian-product-is-random-access*/<Const, First, Vs...>;

    constexpr reference operator[](difference_type n) const
      requires /*cartesian-product-is-random-access*/<Const, First, Vs...>;

    friend constexpr bool operator==(const /*iterator*/& x, const /*iterator*/& y)
      requires equality_comparable<iterator_t</*maybe-const*/<Const, First>>>;

    friend constexpr bool operator==(const /*iterator*/& x, default_sentinel_t);

    friend constexpr auto operator<=>(const /*iterator*/& x, const /*iterator*/& y)
      requires /*all-random-access*/<Const, First, Vs...>;

    friend constexpr /*iterator*/ operator+(const /*iterator*/& x, difference_type y)
      requires /*cartesian-product-is-random-access*/<Const, First, Vs...>;
    friend constexpr /*iterator*/ operator+(difference_type x, const /*iterator*/& y)
      requires /*cartesian-product-is-random-access*/<Const, First, Vs...>;
    friend constexpr /*iterator*/ operator-(const /*iterator*/& x, difference_type y)
      requires /*cartesian-product-is-random-access*/<Const, First, Vs...>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const /*iterator*/& y)
      requires /*cartesian-is-sized-sentinel*/<Const, iterator_t, First, Vs...>;

    friend constexpr difference_type operator-(const /*iterator*/& i, default_sentinel_t)
      requires /*cartesian-is-sized-sentinel*/<Const, sentinel_t, First, Vs...>;
    friend constexpr difference_type operator-(default_sentinel_t, const /*iterator*/& i)
      requires /*cartesian-is-sized-sentinel*/<Const, sentinel_t, First, Vs...>;

    friend constexpr auto iter_move(const /*iterator*/& i) noexcept(
      /* 见描述 */);

    friend constexpr void iter_swap(const /*iterator*/& l,
                                    const /*iterator*/& r) noexcept(/* 见描述 */)
      requires(indirectly_swappable<iterator_t</*maybe-const*/<Const, First>>> && ... &&
               indirectly_swappable<iterator_t</*maybe-const*/<Const, Vs>>>);

  private:
    using /*Parent*/ = /*maybe-const*/<Const, cartesian_product_view>; // 仅用于阐述
    /*Parent*/* /*parent_*/ = nullptr;                                 // 仅用于阐述
    tuple<iterator_t</*maybe-const*/<Const, First>>,
          iterator_t</*maybe-const*/<Const, Vs>>...>
      /*current_*/; // 仅用于阐述

    template<size_t N = sizeof...(Vs)>
    constexpr void /*next*/(); // 仅用于阐述

    template<size_t N = sizeof...(Vs)>
    constexpr void /*prev*/(); // 仅用于阐述

    template<class Tuple>
    constexpr difference_type /*distance-from*/(const Tuple& t) const; // 仅用于阐述

    constexpr /*iterator*/(
      /*Parent*/& parent,
      tuple<iterator_t</*maybe-const*/<Const, First>>,
            iterator_t</*maybe-const*/<Const, Vs>>...> current); // 仅用于阐述
  };
}

类模板 std::ranges::cache_latest_view

namespace std::ranges {
  template<input_range V>
    requires view<V>
  class cache_latest_view : public view_interface<cache_latest_view<V>>
  {
    V /*base_*/ = V(); // 仅用于阐述
    using /*cache-t*/ =
      conditional_t<is_reference_v<range_reference_t<V>>, // 仅用于阐述
                    add_pointer_t<range_reference_t<V>>,
                    range_reference_t<V>>;

    /*non-propagating-cache*/</*cache-t*/> /*cache_*/; // 仅用于阐述

    // 类 cache_latest_view::iterator
    class /*iterator*/; // 仅用于阐述
    // 类 cache_latest_view::sentinel
    class /*sentinel*/; // 仅用于阐述

  public:
    cache_latest_view()
      requires default_initializable<V>
    = default;
    constexpr explicit cache_latest_view(V base);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin();
    constexpr auto end();

    constexpr auto size()
      requires sized_range<V>;
    constexpr auto size() const
      requires sized_range<const V>;
  };

  template<class R>
  cache_latest_view(R&&) -> cache_latest_view<views::all_t<R>>;
}

类模板 std::ranges::cache_latest_view::iterator

namespace std::ranges {
  template<input_range V>
    requires view<V>
  class cache_latest_view<V>::/*iterator*/
  {
    cache_latest_view* /*parent_*/; // 仅用于阐述
    iterator_t<V> /*current_*/;     // 仅用于阐述

    constexpr explicit /*iterator*/(cache_latest_view& parent); // 仅用于阐述

  public:
    using difference_type                   = range_difference_t<V>;
    using value_type                        = range_value_t<V>;
    using iterator_concept                  = input_iterator_tag;

    /*iterator*/(/*iterator*/&&)            = default;
    /*iterator*/& operator=(/*iterator*/&&) = default;

    constexpr iterator_t<V> base() &&;
    constexpr const iterator_t<V>& base() const& noexcept;

    constexpr range_reference_t<V>& operator*() const;

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);

    friend constexpr range_rvalue_reference_t<V> iter_move(
      const /*iterator*/& i) noexcept(noexcept(ranges::iter_move(i./*current_*/)));

    friend constexpr void iter_swap(
      const /*iterator*/& x,
      const /*iterator*/& y) noexcept(noexcept(ranges::iter_swap(x./*current_*/,
                                                                 y./*current_*/)))
      requires indirectly_swappable<iterator_t<V>>;
  };
}

类模板 std::ranges::cache_latest_view::sentinel

namespace std::ranges {
  template<input_range V>
    requires view<V>
  class cache_latest_view<V>::/*sentinel*/
  {
    sentinel_t<V> /*end_*/ = sentinel_t<V>(); // 仅用于阐述

    constexpr explicit /*sentinel*/(cache_latest_view& parent); // 仅用于阐述

  public:
    /*sentinel*/() = default;

    constexpr sentinel_t<V> base() const;

    friend constexpr bool operator==(const /*iterator*/& x, const /*sentinel*/& y);

    friend constexpr range_difference_t<V> operator-(const /*iterator*/& x,
                                                     const /*sentinel*/& y)
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
    friend constexpr range_difference_t<V> operator-(const /*sentinel*/& x,
                                                     const /*iterator*/& y)
      requires sized_sentinel_for<sentinel_t<V>, iterator_t<V>>;
  };
}

类模板 std::ranges::to_input_view

namespace std::ranges {
  template<input_range V>
    requires view<V>
  class to_input_view : public view_interface<to_input_view<V>>
  {
    V /*base_*/ = V(); // 仅用于阐述

    // 类模板 to_input_view::iterator
    template<bool Const>
    class /*iterator*/; // 仅用于阐述

  public:
    to_input_view()
      requires default_initializable<V>
    = default;
    constexpr explicit to_input_view(V base);

    constexpr V base() const&
      requires copy_constructible<V>
    {
      return /*base_*/;
    }
    constexpr V base() && { return std::move(/*base_*/); }

    constexpr auto begin()
      requires(!/*simple-view*/<V>);
    constexpr auto begin() const
      requires range<const V>;

    constexpr auto end()
      requires(!/*simple-view*/<V>);
    constexpr auto end() const
      requires range<const V>;

    constexpr auto size()
      requires sized_range<V>;
    constexpr auto size() const
      requires sized_range<const V>;
  };

  template<class R>
  to_input_view(R&&) -> to_input_view<views::all_t<R>>;
}

类模板 std::ranges::to_input_view::iterator

namespace std::ranges {
  template<input_range V>
    requires view<V>
  template<bool Const>
  class to_input_view<V>::/*iterator*/
  {
    using /*Base*/                    = /*maybe-const*/<Const, V>; // 仅用于阐述

    iterator_t</*Base*/> /*current_*/ = iterator_t</*Base*/>(); // 仅用于阐述

    constexpr explicit /*iterator*/(iterator_t</*Base*/> current); // 仅用于阐述

  public:
    using difference_type  = range_difference_t</*Base*/>;
    using value_type       = range_value_t</*Base*/>;
    using iterator_concept = input_iterator_tag;

    /*iterator*/()
      requires default_initializable<iterator_t</*Base*/>>
    = default;

    /*iterator*/(/*iterator*/&&)            = default;
    /*iterator*/& operator=(/*iterator*/&&) = default;

    constexpr /*iterator*/(/*iterator*/<!Const> i)
      requires Const && convertible_to<iterator_t<V>, iterator_t</*Base*/>>;

    constexpr iterator_t</*Base*/> base() &&;
    constexpr const iterator_t</*Base*/>& base() const& noexcept;

    constexpr decltype(auto) operator*() const { return */*current_*/; }

    constexpr /*iterator*/& operator++();
    constexpr void operator++(int);

    friend constexpr bool operator==(const /*iterator*/& x,
                                     const sentinel_t</*Base*/>& y);

    friend constexpr difference_type operator-(const sentinel_t</*Base*/>& y,
                                               const /*iterator*/& x)
      requires sized_sentinel_for<sentinel_t</*Base*/>, iterator_t</*Base*/>>;
    friend constexpr difference_type operator-(const /*iterator*/& x,
                                               const sentinel_t</*Base*/>& y)
      requires sized_sentinel_for<sentinel_t</*Base*/>, iterator_t</*Base*/>>;

    friend constexpr range_rvalue_reference_t</*Base*/> iter_move(
      const /*iterator*/& i) noexcept(noexcept(ranges::iter_move(i./*current_*/)));

    friend constexpr void iter_swap(
      const /*iterator*/& x,
      const /*iterator*/& y) noexcept(noexcept(ranges::iter_swap(x./*current_*/,
                                                                 y./*current_*/)))
      requires indirectly_swappable<iterator_t</*Base*/>>;
  };
}

缺陷报告

下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。

缺陷报告 应用于 出版时的行为 正确行为
LWG 3914 C++23 概要中没有正确指定 std::ranges::enumerate_view 的约束 已修正