# 标准库头文件 <memory>

< cpp‎ | header

此头文件是动态内存管理库的一部分。

### 包含
<compare> (C++20) | 三路比较运算符支持
### 类
##### 指针特征
pointer_traits (C++11) | 提供关于指针式类型的信息 (类模板)
##### 垃圾收集器支持
pointer_safety (C++11)(C++23 中移除) | 列出指针安全模式 (枚举)
##### 分配器
allocator | 默认的分配器 (类模板)
allocator_traits (C++11) | 提供关于分配器类型的信息 (类模板)
allocation_result (C++23) | 记录由 `allocate_at_least` 分配的存储的地址与实际大小 (类模板)
allocator_arg_t (C++11) | 标签类型，用于选择具分配器的构造函数重载 (类)
uses_allocator (C++11) | 检查指定的类型是否支持使用分配器的构造 (类模板)
##### 未初始化存储
raw_storage_iterator (C++17 中弃用)(C++20 中移除) | 允许标准算法存储结果于未初始化内存的迭代器 (类模板)
##### 智能指针
unique_ptr (C++11) | 拥有独有对象所有权语义的智能指针 (类模板)
shared_ptr (C++11) | 拥有共享对象所有权语义的智能指针 (类模板)
weak_ptr (C++11) | 到 std::shared_ptr 所管理对象的弱引用 (类模板)
auto_ptr (C++17 中移除) | 拥有严格对象所有权语义的智能指针 (类模板)
##### 辅助类
std::atomic<std::shared_ptr> (C++20) | 原子共享指针 (类模板特化)
std::atomic<std::weak_ptr> (C++20) | 原子弱指针 (类模板特化)
owner_less (C++11) | 提供基于所有者的，共享指针和弱指针的混合类型的排序 (类模板)
enable_shared_from_this (C++11) | 允许对象创建指代自身的 `shared_ptr` (类模板)
bad_weak_ptr (C++11) | 访问指向已销毁对象的 `weak_ptr` 时抛出的异常 (类)
default_delete (C++11) | `unique_ptr` 的默认删除器 (类模板)
std::hash<std::unique_ptr> (C++11) | std::unique_ptr 的散列支持 (类模板特化)
std::hash<std::shared_ptr> (C++11) | std::shared_ptr 的散列支持 (类模板特化)
##### 智能指针适配器
out_ptr_t (C++23) | 与外来指针设置器交互，并在析构时重设智能指针 (类模板)
inout_ptr_t (C++23) | 与外来指针设置器交互，从智能指针获得初始指针值，并在析构时重设它 (类模板)
##### 前置声明
定义于头文件 `<functional>`
hash (C++11) | 散列函数对象 (类模板)
定义于头文件 `<atomic>`
atomic (C++11) | atomic 类模板及其针对布尔、整型和指针类型的特化 (类模板)
### 常量
allocator_arg (C++11) | 用于选择具分配器的构造函数的 std::allocator_arg_t 对象 (常量)
### 函数
##### 分配器
allocate_at_least (C++23) | 经由分配器分配至少与请求的大小一样大的存储 (函数模板)
##### 杂项
to_address (C++20) | 从指针式类型获得裸指针 (函数模板)
addressof (C++11) | 获得对象的实际地址，即使其重载了 & 运算符 (函数模板)
align (C++11) | 对齐缓冲区中的指针 (函数)
assume_aligned (C++20) | 告知编译器指针已对齐 (函数模板)
##### 垃圾收集器支持
declare_reachable (C++11)(C++23 中移除) | 声明一个对象不能被回收 (函数)
undeclare_reachable (C++11)(C++23 中移除) | 声明一个对象可以被回收 (函数模板)
declare_no_pointers (C++11)(C++23 中移除) | 声明该内存区域不含可追踪指针 (函数)
undeclare_no_pointers (C++11)(C++23 中移除) | 取消 std::declare_no_pointers 的效果 (函数)
get_pointer_safety (C++11)(C++23 中移除) | 返回当前的指针安全模式 (函数)
##### 未初始化存储
uninitialized_copy | 将范围内的对象复制到未初始化的内存区域 (函数模板)
uninitialized_copy_n (C++11) | 将指定数量的对象复制到未初始化的内存区域 (函数模板)
uninitialized_fill | 复制一个对象到以范围定义的未初始化内存区域 (函数模板)
uninitialized_fill_n | 复制一个对象到以起点和计数定义的未初始化内存区域 (函数模板)
uninitialized_move (C++17) | 移动一个范围的对象到未初始化的内存区域 (函数模板)
uninitialized_move_n (C++17) | 移动一定数量对象到未初始化内存区域 (函数模板)
uninitialized_default_construct (C++17) | 在范围所定义的未初始化的内存区域以默认初始化构造对象 (函数模板)
uninitialized_default_construct_n (C++17) | 在起始和计数所定义的未初始化内存区域用默认初始化构造对象 (函数模板)
uninitialized_value_construct (C++17) | 在范围所定义的未初始化内存中用值初始化构造对象 (函数模板)
uninitialized_value_construct_n (C++17) | 在起始和计数所定义的未初始化内存区域以值初始化构造对象 (函数模板)
construct_at (C++20) | 在给定地址创建对象 (函数模板)
destroy_at (C++17) | 销毁在给定地址的对象 (函数模板)
destroy (C++17) | 销毁一个范围中的对象 (函数模板)
destroy_n (C++17) | 销毁范围中一定数量的对象 (函数模板)
get_temporary_buffer (C++17 中弃用)(C++20 中移除) | 获得未初始化存储 (函数模板)
return_temporary_buffer (C++17 中弃用)(C++20 中移除) | 释放未初始化存储 (函数模板)
##### 智能指针非成员操作
make_unique make_unique_for_overwrite (C++14)(C++20) | 创建管理一个新对象的独占指针 (函数模板)
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20 中移除)(C++20) | 与另一个 `unique_ptr` 或 nullptr 进行比较 (函数模板)
make_shared make_shared_for_overwrite (C++20) | 创建管理一个新对象的共享指针 (函数模板)
allocate_shared allocate_shared_for_overwrite (C++20) | 创建管理一个用分配器分配的新对象的共享指针 (函数模板)
static_pointer_cast dynamic_pointer_cast const_pointer_cast reinterpret_pointer_cast (C++17) | 应用 `static_cast`、`dynamic_cast`、`const_cast` 或 `reinterpret_cast` 到被存储指针 (函数模板)
get_deleter | 返回指定类型中的删除器，若其拥有 (函数模板)
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20) | 与另一个 `shared_ptr` 或 nullptr 进行比较 (函数模板)
operator<< | 将存储的指针的值输出到输出流 (函数模板)
std::swap(std::unique_ptr) (C++11) | 特化 std::swap 算法 (函数模板)
std::swap(std::weak_ptr) (C++11) | 特化 std::swap 算法 (函数模板)
std::swap(std::shared_ptr) (C++11) | 特化 std::swap 算法 (函数模板)
##### 智能指针适配器创建
out_ptr (C++23) | 以关联的智能指针和重设参数创建 `out_ptr_t` (函数模板)
inout_ptr (C++23) | 以关联的智能指针和重设参数创建 `inout_ptr_t` (函数模板)

std::atomic_is_lock_free(std::shared_ptr)std::atomic_load(std::shared_ptr)std::atomic_load_explicit(std::shared_ptr)std::atomic_store(std::shared_ptr)std::atomic_store_explicit(std::shared_ptr)std::atomic_exchange(std::shared_ptr)std::atomic_exchange_explicit(std::shared_ptr)std::atomic_compare_exchange_weak(std::shared_ptr)std::atomic_compare_exchange_strong(std::shared_ptr)std::atomic_compare_exchange_weak_explicit(std::shared_ptr)std::atomic_compare_exchange_strong_explicit(std::shared_ptr) (C++20 中弃用) | 特化的原子操作 (函数模板)

### 仿函数实体
定义于命名空间 `std::ranges`
##### 未初始化存储
ranges::uninitialized_copy (C++20) | 复制元素范围到未初始化的内存区域 (niebloid)
ranges::uninitialized_copy_n (C++20) | 复制一定量元素到未初始化的内存区域 (niebloid)
ranges::uninitialized_fill (C++20) | 复制一个对象到范围所定义的未初始化的内存区域 (niebloid)
ranges::uninitialized_fill_n (C++20) | 复制一个对象到起始与计数所定义的未初始化的内存区域 (niebloid)
ranges::uninitialized_move (C++20) | 移动对象范围到未初始化的内存区域 (niebloid)
ranges::uninitialized_move_n (C++20) | 移动一定量对象到未初始化的内存区域 (niebloid)
ranges::uninitialized_default_construct (C++20) | 在范围所定义的未初始化的内存区域以默认初始化构造对象 (niebloid)
ranges::uninitialized_default_construct_n (C++20) | 在起始与计数所定义的未初始化的内存区域以默认初始化构造对象 (niebloid)
ranges::uninitialized_value_construct (C++20) | 在范围所定义的未初始化的内存区域以值初始化构造对象 (niebloid)
ranges::uninitialized_value_construct_n (C++20) | 在起始与计数所定义的未初始化的内存区域以值初始化构造对象 (niebloid)
ranges::construct_at (C++20) | 在给定地址创建对象 (niebloid)
ranges::destroy_at (C++20) | 销毁位于给定地址的元素 (niebloid)
ranges::destroy (C++20) | 销毁范围中的元素 (niebloid)
ranges::destroy_n (C++20) | 销毁范围中一定量的元素 (niebloid)

### 概要

    #include <compare>

    namespace std {
      // 指针特征
      template<class Ptr> struct pointer_traits;
      template<class T> struct pointer_traits<T*>;

      // 指针转换
      template<class T>
        constexpr T* to_address(T* p) noexcept;
      template<class Ptr>
        constexpr auto to_address(const Ptr& p) noexcept;

      // 指针对齐
      void* align(size_t alignment, size_t size, void*& ptr, size_t& space);
      template<size_t N, class T>
        [[nodiscard]] constexpr T* assume_aligned(T* ptr);

      // 分配器参数标签
      struct allocator_arg_t { explicit allocator_arg_t() = default; };
      inline constexpr allocator_arg_t allocator_arg{};

      // uses_allocator
      template<class T, class Alloc> struct uses_allocator;

      // uses_allocator
      template<class T, class Alloc>
        inline constexpr bool uses_allocator_v = uses_allocator<T, Alloc>::value;

      // 使用分配器构造
      template<class T, class Alloc, class... Args>
        constexpr auto uses_allocator_construction_args(const Alloc& alloc,
                                                        Args&&... args) noexcept;
      template<class T, class Alloc, class Tuple1, class Tuple2>
        constexpr auto uses_allocator_construction_args(const Alloc& alloc, piecewise_construct_t,
                                                        Tuple1&& x, Tuple2&& y) noexcept;
      template<class T, class Alloc>
        constexpr auto uses_allocator_construction_args(const Alloc& alloc) noexcept;
      template<class T, class Alloc, class U, class V>
        constexpr auto uses_allocator_construction_args(const Alloc& alloc,
                                                        U&& u, V&& v) noexcept;
      template<class T, class Alloc, class U, class V>
        constexpr auto uses_allocator_construction_args(const Alloc& alloc,
                                                        const pair<U, V>& pr) noexcept;
      template<class T, class Alloc, class U, class V>
        constexpr auto uses_allocator_construction_args(const Alloc& alloc,
                                                        pair<U, V>&& pr) noexcept;
      template<class T, class Alloc, class... Args>
        constexpr T make_obj_using_allocator(const Alloc& alloc, Args&&... args);
      template<class T, class Alloc, class... Args>
        constexpr T* uninitialized_construct_using_allocator(T* p, const Alloc& alloc,
                                                             Args&&... args);

      // 分配器特征
      template<class Alloc> struct allocator_traits;

      template<class Pointer>
      struct allocation_result {
        Pointer ptr;
        size_t count;
      };

      template<class Allocator>
        [[nodiscard]] constexpr allocation_result<typename allocator_traits<Allocator>::pointer>
          allocate_at_least(Allocator& a, size_t n);

      // 默认分配器
      template<class T> class allocator;
      template<class T, class U>
        constexpr bool operator==(const allocator<T>&, const allocator<U>&) noexcept;

      // addressof
      template<class T>
        constexpr T* addressof(T& r) noexcept;
      template<class T>
        const T* addressof(const T&&) = delete;

      // 特化的算法
      // 特殊内存概念
      template<class I>
        concept no-throw-input-iterator = /* 见描述 */;    // 仅用于阐释
      template<class I>
        concept no-throw-forward-iterator = /* 见描述 */;  // 仅用于阐释
      template<class S, class I>
        concept no-throw-sentinel-for = /* 见描述 */;      // 仅用于阐释
      template<class R>
        concept no-throw-input-range = /* 见描述 */;       // 仅用于阐释
      template<class R>
        concept no-throw-forward-range = /* 见描述 */;     // 仅用于阐释

      template<class NoThrowForwardIt>
        void uninitialized_default_construct(NoThrowForwardIt first,
                                             NoThrowForwardIt last);
      template<class ExecutionPolicy, class NoThrowForwardIt>
        void uninitialized_default_construct(ExecutionPolicy&& exec,
                                             NoThrowForwardIt first,
                                             NoThrowForwardIt last);
      template<class NoThrowForwardIt, class Size>
        NoThrowForwardIt
          uninitialized_default_construct_n(NoThrowForwardIt first, Size n);
      template<class ExecutionPolicy, class NoThrowForwardIt, class Size>
        NoThrowForwardIt
          uninitialized_default_construct_n(ExecutionPolicy&& exec,
                                            NoThrowForwardIt first, Size n);

      namespace ranges {
        template<no-throw-forward-iterator I, no-throw-sentinel-for<I> S>
          requires default_initializable<iter_value_t<I>>
            I uninitialized_default_construct(I first, S last);
        template<no-throw-forward-range R>
          requires default_initializable<range_value_t<R>>
            borrowed_iterator_t<R> uninitialized_default_construct(R&& r);

        template<no-throw-forward-iterator I>
          requires default_initializable<iter_value_t<I>>
            I uninitialized_default_construct_n(I first, iter_difference_t<I> n);
      }

      template<class NoThrowForwardIterator>
        void uninitialized_value_construct(NoThrowForwardIterator first,
                                           NoThrowForwardIterator last);
      template<class ExecutionPolicy, class NoThrowForwardIt>
        void uninitialized_value_construct(ExecutionPolicy&& exec,
                                           NoThrowForwardIt first,
                                           NoThrowForwardIt last);
      template<class NoThrowForwardIt, class Size>
        NoThrowForwardIt
          uninitialized_value_construct_n(NoThrowForwardIt first, Size n);
      template<class ExecutionPolicy, class NoThrowForwardIt, class Size>
        NoThrowForwardIt
          uninitialized_value_construct_n(ExecutionPolicy&& exec,
                                          NoThrowForwardIt first, Size n);

      namespace ranges {
        template<no-throw-forward-iterator I, no-throw-sentinel-for<I> S>
          requires default_initializable<iter_value_t<I>>
            I uninitialized_value_construct(I first, S last);
        template<no-throw-forward-range R>
          requires default_initializable<range_value_t<R>>
            borrowed_iterator_t<R> uninitialized_value_construct(R&& r);

        template<no-throw-forward-iterator I>
          requires default_initializable<iter_value_t<I>>
            I uninitialized_value_construct_n(I first, iter_difference_t<I> n);
      }

      template<class InputIt, class NoThrowForwardIt>
        NoThrowForwardIt uninitialized_copy(InputIt first, InputIt last,
                                            NoThrowForwardIt result);
      template<class ExecutionPolicy, class ForwardIt, class NoThrowForwardIt>
        NoThrowForwardIt uninitialized_copy(ExecutionPolicy&& exec,
                                            ForwardIt first, ForwardIt last,
                                            NoThrowForwardIt result);
      template<class InputIt, class Size, class NoThrowForwardIt>
        NoThrowForwardIt uninitialized_copy_n(InputIt first, Size n,
                                              NoThrowForwardIt result);
      template<class ExecutionPolicy, class ForwardIt, class Size,
               class NoThrowForwardIt>
        NoThrowForwardIt uninitialized_copy_n(ExecutionPolicy&& exec,
                                              ForwardIt first, Size n,
                                              NoThrowForwardIt result);

      namespace ranges {
        template<class I, class O>
          using uninitialized_copy_result = in_out_result<I, O>;
        template<input_iterator I, sentinel_for<I> S1,
                 no-throw-forward-iterator O, no-throw-sentinel-for<O> S2>
          requires constructible_from<iter_value_t<O>, iter_reference_t<I>>
            uninitialized_copy_result<I, O>
              uninitialized_copy(I ifirst, S1 ilast, O ofirst, S2 olast);
        template<input_range IR, no-throw-forward-range OR>
          requires constructible_from<range_value_t<OR>, range_reference_t<IR>>
            uninitialized_copy_result<borrowed_iterator_t<IR>, borrowed_iterator_t<OR>>
              uninitialized_copy(IR&& in_range, OR&& out_range);

        template<class I, class O>
          using uninitialized_copy_n_result = in_out_result<I, O>;
        template<input_iterator I, no-throw-forward-iterator O, no-throw-sentinel-for<O> S>
          requires constructible_from<iter_value_t<O>, iter_reference_t<I>>
            uninitialized_copy_n_result<I, O>
              uninitialized_copy_n(I ifirst, iter_difference_t<I> n, O ofirst, S olast);
      }

      template<class InputIt, class NoThrowForwardIt>
        NoThrowForwardIt uninitialized_move(InputIt first, InputIt last,
                                            NoThrowForwardIt result);
      template<class ExecutionPolicy, class ForwardIt, class NoThrowForwardIt>
        NoThrowForwardIt uninitialized_move(ExecutionPolicy&& exec,
                                            ForwardIt first, ForwardIt last,
                                            NoThrowForwardIt result);
      template<class InputIt, class Size, class NoThrowForwardIt>
        pair<InputIt, NoThrowForwardIt>
          uninitialized_move_n(InputIt first, Size n, NoThrowForwardIt result);
      template<class ExecutionPolicy, class ForwardIt, class Size,
               class NoThrowForwardIt>
        pair<ForwardIt, NoThrowForwardIt>
          uninitialized_move_n(ExecutionPolicy&& exec,
                               ForwardIt first, Size n, NoThrowForwardIt result);

      namespace ranges {
        template<class I, class O>
          using uninitialized_move_result = in_out_result<I, O>;
        template<input_iterator I, sentinel_for<I> S1,
                 no-throw-forward-iterator O, no-throw-sentinel-for<O> S2>
          requires constructible_from<iter_value_t<O>, iter_rvalue_reference_t<I>>
            uninitialized_move_result<I, O>
              uninitialized_move(I ifirst, S1 ilast, O ofirst, S2 olast);
        template<input_range IR, no-throw-forward-range OR>
          requires constructible_from<range_value_t<OR>, range_rvalue_reference_t<IR>>
            uninitialized_move_result<borrowed_iterator_t<IR>, borrowed_iterator_t<OR>>
              uninitialized_move(IR&& in_range, OR&& out_range);

        template<class I, class O>
          using uninitialized_move_n_result = in_out_result<I, O>;
        template<input_iterator I,
                 no-throw-forward-iterator O, no-throw-sentinel-for<O> S>
          requires constructible_from<iter_value_t<O>, iter_rvalue_reference_t<I>>
            uninitialized_move_n_result<I, O>
              uninitialized_move_n(I ifirst, iter_difference_t<I> n, O ofirst, S olast);
      }

      template<class NoThrowForwardIt, class T>
        void uninitialized_fill(NoThrowForwardIt first, NoThrowForwardIt last,
                                const T& x);
      template<class ExecutionPolicy, class NoThrowForwardIt, class T>
        void uninitialized_fill(ExecutionPolicy&& exec,
                                NoThrowForwardIt first, NoThrowForwardIt last,
                                const T& x);
      template<class NoThrowForwardIt, class Size, class T>
        NoThrowForwardIt
          uninitialized_fill_n(NoThrowForwardIt first, Size n, const T& x);
      template<class ExecutionPolicy, class NoThrowForwardIt, class Size, class T>
        NoThrowForwardIt
          uninitialized_fill_n(ExecutionPolicy&& exec,
                               NoThrowForwardIt first, Size n, const T& x);

      namespace ranges {
        template<no-throw-forward-iterator I, no-throw-sentinel-for<I> S, class T>
          requires constructible_from<iter_value_t<I>, const T&>
            I uninitialized_fill(I first, S last, const T& x);
        template<no-throw-forward-range R, class T>
          requires constructible_from<range_value_t<R>, const T&>
            borrowed_iterator_t<R> uninitialized_fill(R&& r, const T& x);

        template<no-throw-forward-iterator I, class T>
          requires constructible_from<iter_value_t<I>, const T&>
            I uninitialized_fill_n(I first, iter_difference_t<I> n, const T& x);
      }

      // construct_at
      template<class T, class... Args>
        constexpr T* construct_at(T* location, Args&&... args);

      namespace ranges {
        template<class T, class... Args>
          constexpr T* construct_at(T* location, Args&&... args);
      }

      // destroy
      template<class T>
        constexpr void destroy_at(T* location);
      template<class NoThrowForwardIt>
        constexpr void destroy(NoThrowForwardIt first, NoThrowForwardIt last);
      template<class ExecutionPolicy, class NoThrowForwardIt>
        void destroy(ExecutionPolicy&& exec,
                     NoThrowForwardIt first, NoThrowForwardIt last);
      template<class NoThrowForwardIt, class Size>
        constexpr NoThrowForwardIt destroy_n(NoThrowForwardIt first, Size n);
      template<class ExecutionPolicy, class NoThrowForwardIt, class Size>
        NoThrowForwardIt destroy_n(ExecutionPolicy&& exec,
                                   NoThrowForwardIt first, Size n);

      namespace ranges {
        template<destructible T>
          constexpr void destroy_at(T* location) noexcept;

        template<no-throw-input-iterator I, no-throw-sentinel-for<I> S>
          requires destructible<iter_value_t<I>>
            constexpr I destroy(I first, S last) noexcept;
        template<no-throw-input-range R>
          requires destructible<range_value_t<R>>
            constexpr borrowed_iterator_t<R> destroy(R&& r) noexcept;

        template<no-throw-input-iterator I>
          requires destructible<iter_value_t<I>>
            constexpr I destroy_n(I first, iter_difference_t<I> n) noexcept;
      }

      // 类模板 unique_ptr
      template<class T> struct default_delete;
      template<class T> struct default_delete<T[]>;
      template<class T, class D = default_delete<T>> class unique_ptr;
      template<class T, class D> class unique_ptr<T[], D>;

      template<class T, class... Args>
        unique_ptr<T> make_unique(Args&&... args);                                  // T 非数组
      template<class T>
        unique_ptr<T> make_unique(size_t n);                                        // T 为 U[]
      template<class T, class... Args>
        /* 未指明 */ make_unique(Args&&...) = delete;                                // T 为 U[N]

      template<class T>
        unique_ptr<T> make_unique_for_overwrite();                                  // T 非数组
      template<class T>
        unique_ptr<T> make_unique_for_overwrite(size_t n);                          // T 为 U[]
      template<class T, class... Args>
        /* 未指明 */ make_unique_for_overwrite(Args&&...) = delete;                  // T 为 U[N]

      template<class T, class D>
        void swap(unique_ptr<T, D>& x, unique_ptr<T, D>& y) noexcept;

      template<class T1, class D1, class T2, class D2>
        bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
      template<class T1, class D1, class T2, class D2>
        bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
      template<class T1, class D1, class T2, class D2>
        bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
      template<class T1, class D1, class T2, class D2>
        bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
      template<class T1, class D1, class T2, class D2>
        bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
      template<class T1, class D1, class T2, class D2>
        requires three_way_comparable_with<typename unique_ptr<T1, D1>::pointer,
                                           typename unique_ptr<T2, D2>::pointer>
        compare_three_way_result_t<typename unique_ptr<T1, D1>::pointer,
                                   typename unique_ptr<T2, D2>::pointer>
          operator<=>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);

      template<class T, class D>
        bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
      template<class T, class D>
        bool operator<(const unique_ptr<T, D>& x, nullptr_t);
      template<class T, class D>
        bool operator<(nullptr_t, const unique_ptr<T, D>& y);
      template<class T, class D>
        bool operator>(const unique_ptr<T, D>& x, nullptr_t);
      template<class T, class D>
        bool operator>(nullptr_t, const unique_ptr<T, D>& y);
      template<class T, class D>
        bool operator<=(const unique_ptr<T, D>& x, nullptr_t);
      template<class T, class D>
        bool operator<=(nullptr_t, const unique_ptr<T, D>& y);
      template<class T, class D>
        bool operator>=(const unique_ptr<T, D>& x, nullptr_t);
      template<class T, class D>
        bool operator>=(nullptr_t, const unique_ptr<T, D>& y);
      template<class T, class D>
        requires three_way_comparable<typename unique_ptr<T, D>::pointer>
        compare_three_way_result_t<typename unique_ptr<T, D>::pointer>
          operator<=>(const unique_ptr<T, D>& x, nullptr_t);

      template<class E, class T, class Y, class D>
        basic_ostream<E, T>& operator<<(basic_ostream<E, T>& os, const unique_ptr<Y, D>& p);

      // 类 bad_weak_ptr
      class bad_weak_ptr;

      // 类模板 shared_ptr
      template<class T> class shared_ptr;

      // shared_ptr 创建
      template<class T, class... Args>
        shared_ptr<T> make_shared(Args&&... args);                                  // T 非数组
      template<class T, class A, class... Args>
        shared_ptr<T> allocate_shared(const A& a, Args&&... args);                  // T 非数组

      template<class T>
        shared_ptr<T> make_shared(size_t N);                                        // T 为 U[]
      template<class T, class A>
        shared_ptr<T> allocate_shared(const A& a, size_t N);                        // T 为 U[]

      template<class T>
        shared_ptr<T> make_shared();                                                // T 为 U[N]
      template<class T, class A>
        shared_ptr<T> allocate_shared(const A& a);                                  // T 为 U[N]

      template<class T>
        shared_ptr<T> make_shared(size_t N, const remove_extent_t<T>& u);           // T 为 U[]
      template<class T, class A>
        shared_ptr<T> allocate_shared(const A& a, size_t N,
                                      const remove_extent_t<T>& u);                 // T 为 U[]

      template<class T>
        shared_ptr<T> make_shared(const remove_extent_t<T>& u);                     // T 为 U[N]
      template<class T, class A>
        shared_ptr<T> allocate_shared(const A& a, const remove_extent_t<T>& u);     // T 为 U[N]

      template<class T>
        shared_ptr<T> make_shared_for_overwrite();                                  // T 非 U[]
      template<class T, class A>
        shared_ptr<T> allocate_shared_for_overwrite(const A& a);                    // T 非 U[]

      template<class T>
        shared_ptr<T> make_shared_for_overwrite(size_t N);                          // T 为 U[]
      template<class T, class A>
        shared_ptr<T> allocate_shared_for_overwrite(const A& a, size_t N);          // T 为 U[]

      // shared_ptr 比较
      template<class T, class U>
        bool operator==(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
      template<class T, class U>
        strong_ordering operator<=>(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;

      template<class T>
        bool operator==(const shared_ptr<T>& x, nullptr_t) noexcept;
      template<class T>
        strong_ordering operator<=>(const shared_ptr<T>& x, nullptr_t) noexcept;

      // shared_ptr 特化算法
      template<class T>
        void swap(shared_ptr<T>& a, shared_ptr<T>& b) noexcept;

      // shared_ptr 转型
      template<class T, class U>
        shared_ptr<T> static_pointer_cast(const shared_ptr<U>& r) noexcept;
      template<class T, class U>
        shared_ptr<T> static_pointer_cast(shared_ptr<U>&& r) noexcept;
      template<class T, class U>
        shared_ptr<T> dynamic_pointer_cast(const shared_ptr<U>& r) noexcept;
      template<class T, class U>
        shared_ptr<T> dynamic_pointer_cast(shared_ptr<U>&& r) noexcept;
      template<class T, class U>
        shared_ptr<T> const_pointer_cast(const shared_ptr<U>& r) noexcept;
      template<class T, class U>
        shared_ptr<T> const_pointer_cast(shared_ptr<U>&& r) noexcept;
      template<class T, class U>
        shared_ptr<T> reinterpret_pointer_cast(const shared_ptr<U>& r) noexcept;
      template<class T, class U>
        shared_ptr<T> reinterpret_pointer_cast(shared_ptr<U>&& r) noexcept;

      // shared_ptr get_deleter
      template<class D, class T>
        D* get_deleter(const shared_ptr<T>& p) noexcept;

      // shared_ptr I/O
      template<class E, class T, class Y>
        basic_ostream<E, T>& operator<<(basic_ostream<E, T>& os, const shared_ptr<Y>& p);

      // 类模板 weak_ptr
      template<class T> class weak_ptr;

      // weak_ptr 特化算法
      template<class T> void swap(weak_ptr<T>& a, weak_ptr<T>& b) noexcept;

      // 类模板 owner_less
      template<class T = void> struct owner_less;

      // 类模板 enable_shared_from_this
      template<class T> class enable_shared_from_this;

      // 散列支持
      template<class T> struct hash;
      template<class T, class D> struct hash<unique_ptr<T, D>>;
      template<class T> struct hash<shared_ptr<T>>;

      // 原子智能指针
      template<class T> struct atomic;
      template<class T> struct atomic<shared_ptr<T>>;
      template<class T> struct atomic<weak_ptr<T>>;

      // 类模板 out_ptr_t
      template<class Smart, class Pointer, class... Args>
        class out_ptr_t;

      // 函数模板 out_ptr
      template<class Pointer = void, class Smart, class... Args>
        auto out_ptr(Smart& s, Args&&... args);

      // 类模板 inout_ptr_t
      template<class Smart, class Pointer, class... Args>
        class inout_ptr_t;

      // 函数模板 inout_ptr
      template<class Pointer = void, class Smart, class... Args>
        auto inout_ptr(Smart& s, Args&&... args);
    }

    // 弃用
    namespace std {
      template<class T>
        bool atomic_is_lock_free(const shared_ptr<T>* p);

      template<class T>
        shared_ptr<T> atomic_load(const shared_ptr<T>* p);
      template<class T>
        shared_ptr<T> atomic_load_explicit(const shared_ptr<T>* p, memory_order mo);

      template<class T>
        void atomic_store(shared_ptr<T>* p, shared_ptr<T> r);
      template<class T>
        void atomic_store_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);

      template<class T>
        shared_ptr<T> atomic_exchange(shared_ptr<T>* p, shared_ptr<T> r);
      template<class T>
        shared_ptr<T> atomic_exchange_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);

      template<class T>
        bool atomic_compare_exchange_weak(shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
      template<class T>
        bool atomic_compare_exchange_strong(shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
      template<class T>
        bool atomic_compare_exchange_weak_explicit(
          shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
          memory_order success, memory_order failure);
      template<class T>
        bool atomic_compare_exchange_strong_explicit(
          shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
          memory_order success, memory_order failure);
    }

#### 辅助概念

    template<class I>
    concept no-throw-input-iterator = // 仅用于阐释
      input_iterator<I> &&
      is_lvalue_reference_v<iter_reference_t<I>> &&
      same_as<remove_cvref_t<iter_reference_t<I>>, iter_value_t<I>>;

    template<class S, class I>
    concept no-throw-sentinel-for = sentinel_for<S, I>; // 仅用于阐释

    template<class R>
    concept no-throw-input-range = // 仅用于阐释
      ranges::range<R> &&
      no-throw-input-iterator<ranges::iterator_t<R>> &&
      no-throw-sentinel-for<ranges::sentinel_t<R>, ranges::iterator_t<R>>;

    template<class I>
    concept no-throw-forward-iterator = // 仅用于阐释
      no-throw-input-iterator<I> &&
      forward_iterator<I> &&
      no-throw-sentinel-for<I, I>;

    template<class R>
    concept no-throw-forward-range = // 仅用于阐释
      no-throw-input-range<R> &&
      no-throw-forward-iterator<ranges::iterator_t<R>>;

注意：这些名字仅用于阐释，它们不是接口的一部分。

#### 类模板 std::pointer_traits

    namespace std {
      template<class Ptr> struct pointer_traits {
        using pointer         = Ptr;
        using element_type    = /* 见描述 */;
        using difference_type = /* 见描述 */;

        template<class U> using rebind = /* 见描述 */;

        static pointer pointer_to(/* 见描述 */ r);
      };

      template<class T> struct pointer_traits<T*> {
        using pointer         = T*;
        using element_type    = T;
        using difference_type = ptrdiff_t;

        template<class U> using rebind = U*;

        static constexpr pointer pointer_to(/* 见描述 */ r) noexcept;
      };
    }

#### 类 std::allocator_arg_t

    namespace std {
      struct allocator_arg_t { explicit allocator_arg_t() = default; };
      inline constexpr allocator_arg_t allocator_arg{};
    }

#### 类模板 std::allocator_traits

    namespace std {
      template<class Alloc> struct allocator_traits {
        using allocator_type     = Alloc;

        using value_type         = typename Alloc::value_type;

        using pointer            = /* 见描述 */;
        using const_pointer      = /* 见描述 */;
        using void_pointer       = /* 见描述 */;
        using const_void_pointer = /* 见描述 */;

        using difference_type    = /* 见描述 */;
        using size_type          = /* 见描述 */;

        using propagate_on_container_copy_assignment = /* 见描述 */;
        using propagate_on_container_move_assignment = /* 见描述 */;
        using propagate_on_container_swap            = /* 见描述 */;
        using is_always_equal                        = /* 见描述 */;

        template<class T> using rebind_alloc = /* 见描述 */;
        template<class T> using rebind_traits = allocator_traits<rebind_alloc<T>>;

        [[nodiscard]] static pointer allocate(Alloc& a, size_type n);
        [[nodiscard]] static pointer allocate(Alloc& a, size_type n,
                                              const_void_pointer hint);

        static void deallocate(Alloc& a, pointer p, size_type n);

        template<class T, class... Args>
          static void construct(Alloc& a, T* p, Args&&... args);

        template<class T>
          static void destroy(Alloc& a, T* p);

        static size_type max_size(const Alloc& a) noexcept;

        static Alloc select_on_container_copy_construction(const Alloc& rhs);
      };
    }

#### 类模板 std::allocator

    namespace std {
      template<class T> class allocator {
       public:
        using value_type                             = T;
        using size_type                              = size_t;
        using difference_type                        = ptrdiff_t;
        using propagate_on_container_move_assignment = true_type;

        constexpr allocator() noexcept;
        constexpr allocator(const allocator&) noexcept;
        template<class U> constexpr allocator(const allocator<U>&) noexcept;
        constexpr ~allocator();
        constexpr allocator& operator=(const allocator&) = default;

        [[nodiscard]] constexpr T* allocate(size_t n);
        [[nodiscard]] constexpr allocation_result<T*> allocate_at_least(size_t n);
        constexpr void deallocate(T* p, size_t n);

        // 弃用
        using is_always_equal = true_type;
      };
    }

#### 类模板 std::default_delete

    namespace std {
      template<class T> struct default_delete {
        constexpr default_delete() noexcept = default;
        template<class U> default_delete(const default_delete<U>&) noexcept;
        void operator()(T*) const;
      };

      template<class T> struct default_delete<T[]> {
        constexpr default_delete() noexcept = default;
        template<class U> default_delete(const default_delete<U[]>&) noexcept;
        template<class U> void operator()(U* ptr) const;
      };
    }

#### 类模板 std::unique_ptr

    namespace std {
      template<class T, class D = default_delete<T>> class unique_ptr {
      public:
        using pointer      = /* 见描述 */;
        using element_type = T;
        using deleter_type = D;

        // 构造函数
        constexpr unique_ptr() noexcept;
        explicit unique_ptr(pointer p) noexcept;
        unique_ptr(pointer p, /* 见描述 */ d1) noexcept;
        unique_ptr(pointer p, /* 见描述 */ d2) noexcept;
        unique_ptr(unique_ptr&& u) noexcept;
        constexpr unique_ptr(nullptr_t) noexcept;
        template<class U, class E>
          unique_ptr(unique_ptr<U, E>&& u) noexcept;

        // 析构函数
        ~unique_ptr();

        // 赋值
        unique_ptr& operator=(unique_ptr&& u) noexcept;
        template<class U, class E>
          unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
        unique_ptr& operator=(nullptr_t) noexcept;

        // 观察器
        add_lvalue_reference_t<T> operator*() const noexcept(/* 见描述 */);
        pointer operator->() const noexcept;
        pointer get() const noexcept;
        deleter_type& get_deleter() noexcept;
        const deleter_type& get_deleter() const noexcept;
        explicit operator bool() const noexcept;

        // 修改器
        pointer release() noexcept;
        void reset(pointer p = pointer()) noexcept;
        void swap(unique_ptr& u) noexcept;

        // 禁用从左值复制
        unique_ptr(const unique_ptr&) = delete;
        unique_ptr& operator=(const unique_ptr&) = delete;
      };

      template<class T, class D> class unique_ptr<T[], D> {
      public:
        using pointer      = /* 见描述 */;
        using element_type = T;
        using deleter_type = D;

        // 构造函数
        constexpr unique_ptr() noexcept;
        template<class U> explicit unique_ptr(U p) noexcept;
        template<class U> unique_ptr(U p, /* 见描述 */ d) noexcept;
        template<class U> unique_ptr(U p, /* 见描述 */ d) noexcept;
        unique_ptr(unique_ptr&& u) noexcept;
        template<class U, class E>
          unique_ptr(unique_ptr<U, E>&& u) noexcept;
        constexpr unique_ptr(nullptr_t) noexcept;

        // 析构函数
        ~unique_ptr();

        // 赋值
        unique_ptr& operator=(unique_ptr&& u) noexcept;
        template<class U, class E>
          unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
        unique_ptr& operator=(nullptr_t) noexcept;

        // 观察器
        T& operator[](size_t i) const;
        pointer get() const noexcept;
        deleter_type& get_deleter() noexcept;
        const deleter_type& get_deleter() const noexcept;
        explicit operator bool() const noexcept;

        // 修改器
        pointer release() noexcept;
        template<class U> void reset(U p) noexcept;
        void reset(nullptr_t = nullptr) noexcept;
        void swap(unique_ptr& u) noexcept;

        // 禁用从左值复制
        unique_ptr(const unique_ptr&) = delete;
        unique_ptr& operator=(const unique_ptr&) = delete;
      };
    }

#### 类 std::bad_weak_ptr

    namespace std {
      class bad_weak_ptr : public exception {
      public:
        bad_weak_ptr() noexcept;
      };
    }

#### 类模板 std::shared_ptr

    namespace std {
      template<class T> class shared_ptr {
      public:
        using element_type = remove_extent_t<T>;
        using weak_type    = weak_ptr<T>;

        // 构造函数
        constexpr shared_ptr() noexcept;
        constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
        template<class Y>
          explicit shared_ptr(Y* p);
        template<class Y, class D>
          shared_ptr(Y* p, D d);
        template<class Y, class D, class A>
          shared_ptr(Y* p, D d, A a);
        template<class D>
          shared_ptr(nullptr_t p, D d);
        template<class D, class A>
          shared_ptr(nullptr_t p, D d, A a);
        template<class Y>
          shared_ptr(const shared_ptr<Y>& r, element_type* p) noexcept;
        template<class Y>
          shared_ptr(shared_ptr<Y>&& r, element_type* p) noexcept;
        shared_ptr(const shared_ptr& r) noexcept;
        template<class Y>
          shared_ptr(const shared_ptr<Y>& r) noexcept;
        shared_ptr(shared_ptr&& r) noexcept;
        template<class Y>
          shared_ptr(shared_ptr<Y>&& r) noexcept;
        template<class Y>
          explicit shared_ptr(const weak_ptr<Y>& r);
        template<class Y, class D>
          shared_ptr(unique_ptr<Y, D>&& r);

        // 析构函数
        ~shared_ptr();

        // 赋值
        shared_ptr& operator=(const shared_ptr& r) noexcept;
        template<class Y>
          shared_ptr& operator=(const shared_ptr<Y>& r) noexcept;
        shared_ptr& operator=(shared_ptr&& r) noexcept;
        template<class Y>
          shared_ptr& operator=(shared_ptr<Y>&& r) noexcept;
        template<class Y, class D>
          shared_ptr& operator=(unique_ptr<Y, D>&& r);

        // 修改器
        void swap(shared_ptr& r) noexcept;
        void reset() noexcept;
        template<class Y>
          void reset(Y* p);
        template<class Y, class D>
          void reset(Y* p, D d);
        template<class Y, class D, class A>
          void reset(Y* p, D d, A a);

        // 观察器
        element_type* get() const noexcept;
        T& operator*() const noexcept;
        T* operator->() const noexcept;
        element_type& operator[](ptrdiff_t i) const;
        long use_count() const noexcept;
        explicit operator bool() const noexcept;
        template<class U>
          bool owner_before(const shared_ptr<U>& b) const noexcept;
        template<class U>
          bool owner_before(const weak_ptr<U>& b) const noexcept;
      };

      template<class T>
        shared_ptr(weak_ptr<T>) -> shared_ptr<T>;
      template<class T, class D>
        shared_ptr(unique_ptr<T, D>) -> shared_ptr<T>;
    }

#### 类模板 std::weak_ptr

    namespace std {
      template<class T> class weak_ptr {
      public:
        using element_type = remove_extent_t<T>;

        // 构造函数
        constexpr weak_ptr() noexcept;
        template<class Y>
          weak_ptr(const shared_ptr<Y>& r) noexcept;
        weak_ptr(const weak_ptr& r) noexcept;
        template<class Y>
          weak_ptr(const weak_ptr<Y>& r) noexcept;
        weak_ptr(weak_ptr&& r) noexcept;
        template<class Y>
          weak_ptr(weak_ptr<Y>&& r) noexcept;

        // 析构函数
        ~weak_ptr();

        // 赋值
        weak_ptr& operator=(const weak_ptr& r) noexcept;
        template<class Y>
          weak_ptr& operator=(const weak_ptr<Y>& r) noexcept;
        template<class Y>
          weak_ptr& operator=(const shared_ptr<Y>& r) noexcept;
        weak_ptr& operator=(weak_ptr&& r) noexcept;
        template<class Y>
          weak_ptr& operator=(weak_ptr<Y>&& r) noexcept;

        // 修改器
        void swap(weak_ptr& r) noexcept;
        void reset() noexcept;

        // 观察器
        long use_count() const noexcept;
        bool expired() const noexcept;
        shared_ptr<T> lock() const noexcept;
        template<class U>
          bool owner_before(const shared_ptr<U>& b) const noexcept;
        template<class U>
          bool owner_before(const weak_ptr<U>& b) const noexcept;
      };

      template<class T>
        weak_ptr(shared_ptr<T>) -> weak_ptr<T>;
    }

#### 类模板 std::owner_less

    namespace std {
      template<class T = void> struct owner_less;

      template<class T> struct owner_less<shared_ptr<T>> {
        bool operator()(const shared_ptr<T>&, const shared_ptr<T>&) const noexcept;
        bool operator()(const shared_ptr<T>&, const weak_ptr<T>&) const noexcept;
        bool operator()(const weak_ptr<T>&, const shared_ptr<T>&) const noexcept;
      };

      template<class T> struct owner_less<weak_ptr<T>> {
        bool operator()(const weak_ptr<T>&, const weak_ptr<T>&) const noexcept;
        bool operator()(const shared_ptr<T>&, const weak_ptr<T>&) const noexcept;
        bool operator()(const weak_ptr<T>&, const shared_ptr<T>&) const noexcept;
      };

      template<> struct owner_less<void> {
        template<class T, class U>
          bool operator()(const shared_ptr<T>&, const shared_ptr<U>&) const noexcept;
        template<class T, class U>
          bool operator()(const shared_ptr<T>&, const weak_ptr<U>&) const noexcept;
        template<class T, class U>
          bool operator()(const weak_ptr<T>&, const shared_ptr<U>&) const noexcept;
        template<class T, class U>
          bool operator()(const weak_ptr<T>&, const weak_ptr<U>&) const noexcept;

        using is_transparent = /* 未指明 */;
      };
    }

#### 类模板 std::enable_shared_from_this

    namespace std {
      template<class T> class enable_shared_from_this {
      protected:
        constexpr enable_shared_from_this() noexcept;
        enable_shared_from_this(const enable_shared_from_this&) noexcept;
        enable_shared_from_this& operator=(const enable_shared_from_this&) noexcept;
        ~enable_shared_from_this();

      public:
        shared_ptr<T> shared_from_this();
        shared_ptr<T const> shared_from_this() const;
        weak_ptr<T> weak_from_this() noexcept;
        weak_ptr<T const> weak_from_this() const noexcept;

      private:
        mutable weak_ptr<T> weak_this;  // 仅用于阐释
      };
    }

#### 类模板 std::atomic 对 std::shared_ptr 的特化

    namespace std {
      template<class T> struct atomic<shared_ptr<T>> {
        using value_type = shared_ptr<T>;
        static constexpr bool is_always_lock_free = /* 由实现定义 */;

        bool is_lock_free() const noexcept;
        void store(shared_ptr<T> desired, memory_order order = memory_order::seq_cst) noexcept;
        shared_ptr<T> load(memory_order order = memory_order::seq_cst) const noexcept;
        operator shared_ptr<T>() const noexcept;

        shared_ptr<T> exchange(shared_ptr<T> desired,
                               memory_order order = memory_order::seq_cst) noexcept;

        bool compare_exchange_weak(shared_ptr<T>& expected, shared_ptr<T> desired,
                                   memory_order success, memory_order failure) noexcept;
        bool compare_exchange_strong(shared_ptr<T>& expected, shared_ptr<T> desired,
                                     memory_order success, memory_order failure) noexcept;

        bool compare_exchange_weak(shared_ptr<T>& expected, shared_ptr<T> desired,
                                   memory_order order = memory_order::seq_cst) noexcept;
        bool compare_exchange_strong(shared_ptr<T>& expected, shared_ptr<T> desired,
                                     memory_order order = memory_order::seq_cst) noexcept;

        constexpr atomic() noexcept = default;
        atomic(shared_ptr<T> desired) noexcept;
        atomic(const atomic&) = delete;
        void operator=(const atomic&) = delete;
        void operator=(shared_ptr<T> desired) noexcept;

      private:
        shared_ptr<T> p;            // 仅用于阐释
      };
    }

#### 类模板 std::atomic 对 std::weak_ptr 的特化

    namespace std {
      template<class T> struct atomic<weak_ptr<T>> {
        using value_type = weak_ptr<T>;
        static constexpr bool is_always_lock_free = /* 由实现定义 */;

        bool is_lock_free() const noexcept;
        void store(weak_ptr<T> desired, memory_order order = memory_order::seq_cst) noexcept;
        weak_ptr<T> load(memory_order order = memory_order::seq_cst) const noexcept;
        operator weak_ptr<T>() const noexcept;

        weak_ptr<T> exchange(weak_ptr<T> desired,
                             memory_order order = memory_order::seq_cst) noexcept;

        bool compare_exchange_weak(weak_ptr<T>& expected, weak_ptr<T> desired,
                                   memory_order success, memory_order failure) noexcept;
        bool compare_exchange_strong(weak_ptr<T>& expected, weak_ptr<T> desired,
                                     memory_order success, memory_order failure) noexcept;

        bool compare_exchange_weak(weak_ptr<T>& expected, weak_ptr<T> desired,
                                   memory_order order = memory_order::seq_cst) noexcept;
        bool compare_exchange_strong(weak_ptr<T>& expected, weak_ptr<T> desired,
                                     memory_order order = memory_order::seq_cst) noexcept;

        constexpr atomic() noexcept = default;
        atomic(weak_ptr<T> desired) noexcept;
        atomic(const atomic&) = delete;
        void operator=(const atomic&) = delete;
        void operator=(weak_ptr<T> desired) noexcept;

      private:
        weak_ptr<T> p;              // 仅用于阐释
      };
    }

#### 类模板 std::out_ptr_t

    namespace std {
      template<class Smart, class Pointer, class... Args>
      class out_ptr_t {
      public:
        explicit out_ptr_t(Smart&, Args...);
        out_ptr_t(const out_ptr_t&) = delete;

        ~out_ptr_t();

        operator Pointer*() const noexcept;
        operator void**() const noexcept;

      private:
        Smart& s;                   // 仅用于阐释
        tuple<Args...> a;           // 仅用于阐释
        Pointer p;                  // 仅用于阐释
      };
    }

#### 类模板 std::in_out_ptr_t

    namespace std {
      template<class Smart, class Pointer, class... Args>
      class inout_ptr_t {
      public:
        explicit inout_ptr_t(Smart&, Args...);
        inout_ptr_t(const inout_ptr_t&) = delete;

        ~inout_ptr_t();

        operator Pointer*() const noexcept;
        operator void**() const noexcept;

      private:
        Smart& s;                   // 仅用于阐释
        tuple<Args...> a;           // 仅用于阐释
        Pointer p;                  // 仅用于阐释
      };
    }